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Title: Meteoric astronomy: - A treatise on shooting-stars, fire-balls, and aerolites
Author: Kirkwood, Daniel
Language: English
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[Illustration: _Fig. 1._

The Solar System.]



    METEORIC ASTRONOMY:

    A TREATISE

    ON

    SHOOTING-STARS, FIRE-BALLS,

    AND

    AEROLITES.


    BY

    DANIEL KIRKWOOD, LL.D.

    PROFESSOR OF MATHEMATICS IN WASHINGTON AND JEFFERSON COLLEGE.

    [Illustration]

    PHILADELPHIA:
    J. B. LIPPINCOTT & CO.
    1867.



    Entered, according to Act of Congress, in the year 1867, by

    DANIEL KIRKWOOD, LL.D.,

    In the Clerk's Office of the District Court of the United States
    for the Western District of Pennsylvania.



PREFACE.


Aristotle and other ancient writers regarded comets as meteors
generated in the atmosphere. This opinion was generally accepted, even
by the learned, until the observations of Tycho, near the close of the
sixteenth century, showed those mysterious objects to be more distant
than the moon, thus raising them to the dignity of _celestial_ bodies.
An achievement somewhat similar, and certainly no less interesting,
was reserved for the astronomers of the _nineteenth_ century. This was
the great discovery that _shooting-stars, fire-balls, and meteoric
stones, are, like comets, cosmical bodies moving in conic sections
about the sun_. DR. HALLEY was the first to foretell the return of a
comet, and the year 1759 will ever be known in history as that which
witnessed the fulfillment of his prophecy. But in the department of
_meteoric_ astronomy, a similar honor must now be awarded to the late
DR. OLBERS. Soon after the great star-shower of 1833 he inferred from
a comparison of recorded facts that the November display attains
a maximum at intervals of thirty-three or thirty-four years. He
accordingly designated 1866 or 1867 as the time of its probable return;
and the night of November 13th of the former year must always be
memorable as affording the first verification of _his_ prediction. On
that night several thousand meteors were observed in one hour from a
single station. This remarkable display, together with the fact that
another still more brilliant is looked for in November, 1867, has
given meteoric astronomy a more than ordinary degree of interest in
the public mind. To gratify, in some measure, the curiosity which has
been awakened, by presenting in a popular form the principal results of
observation and study in this new field of research, is the main design
of the following work.

The first two chapters contain a popular view of what is known in
regard to the star-showers of August and November, and also of some
other epochs. The third is a description, in chronological order,
of the most important falls of meteoric stones, together with the
phenomena attending their descent. The fourth and following chapters
to the eleventh inclusive, discuss various questions in the theory
of meteors: such, for instance, as the relative number of aerolitic
falls during different parts of the day, and also of the year; the
coexistence of the different forms of meteoric matter in the same
rings; meteoric dust; the stability of the solar system; the doctrine
of a resisting medium; the extent of the atmosphere as indicated by
meteors; the meteoric theory of solar heat; and the phenomena of
variable and temporary stars. The twelfth chapter regards the rings
of Saturn as dense meteoric swarms, and accounts for the principal
interval between them. The thirteenth presents various facts, not
previously noticed, respecting the asteroid zone between Mars and
Jupiter, with suggestions concerning their cause or explanation.

As the nebular hypothesis furnishes a plausible account of the origin
of meteoric streams, it seemed desirable to present an intelligible
view of that celebrated theory. This accordingly forms the subject of
the closing chapter.

The greater part of the following treatise, it is proper to remark, was
written before the publication (in England) of Dr. Phipson's volume on
"Meteors, Aerolites, and Falling-stars." The author has had that work
before him, however, while completing his manuscript, and has availed
himself of some of the accounts there given of recent phenomena.

CANONSBURG, PA, _May, 1867_.



CONTENTS.


                                                                   PAGE
  INTRODUCTION                                                        7


  CHAPTER I.

  The Meteors of November 12th-14th                                  13


  CHAPTER II.

  Other Meteoric Rings                                               26


  CHAPTER III.

  Aerolites                                                          35


  CHAPTER IV.

  Conjectures in Regard to Meteoric Epochs                           50


  CHAPTER V.

  Geographical Distribution of Meteoric Stones--Do
  Aerolitic Falls occur more frequently by Day than by
  Night?--Do Meteorites, Bolides, and the matter of ordinary
  Shooting-stars, coexist in the same Rings?                         56


  CHAPTER VI.

  Phenomena supposed to be Meteoric--Meteoric Dust--Dark Days        65


  CHAPTER VII.

  Researches of Reichenbach--Theory of Meteors--Stability of
  the Solar System--Doctrine of a Resisting Medium                   74

  CHAPTER VIII.

  Does the Number of Aerolitic Falls vary with the Earth's
  Distance from the Sun?--Relative Numbers observed in the
  Forenoon and Afternoon--Extent of the Atmosphere as indicated
  by Meteors                                                         79


  CHAPTER IX.

  The Meteoric Theory of Solar Heat                                  84


  CHAPTER X.

  Will the Meteoric Theory account for the Phenomena of
  Variable and Temporary Stars?                                      92


  CHAPTER XI.

  The Lunar and Solar Theories of the Origin of Aerolites            96


  CHAPTER XII.

  The Rings of Saturn                                               102


  CHAPTER XIII.

  The Asteroid Ring between Mars and Jupiter                        105


  CHAPTER XIV.

  Origin of Meteors--The Nebular Hypothesis                         112


  APPENDIX                                                          123



INTRODUCTION.

A GENERAL VIEW OF THE SOLAR SYSTEM.


THE SOLAR SYSTEM consists of the sun, together with the planets and
comets which revolve around him as the center of their motions. The sun
is the great controlling orb of this system, and the source of light
and heat to its various members. Its magnitude is one million four
hundred thousand times greater than that of the earth, and it contains
more than seven hundred times as much matter as all the planets put
together.

MERCURY is the nearest planet to the sun; its mean distance being about
thirty-seven millions of miles. Its diameter is about three thousand
miles, and it completes its orbital revolution in 88 days.

VENUS, the next member of the system, is sometimes our morning and
sometimes our evening star. Its magnitude is almost exactly the same as
that of the earth. It revolves round the sun in 225 days.

THE EARTH is the third planet from the sun in the order of distance;
the radius of its orbit being about ninety-five millions of miles. It
is attended by one satellite--the moon--the diameter of which is 2160
miles.

MARS is the first planet exterior to the earth's orbit. It is
considerably smaller than the earth, and has no satellite. It revolves
round the sun in 687 days.

THE ASTEROIDS.--Since the commencement of the present century a
remarkable zone of telescopic planets has been discovered immediately
exterior to the orbit of Mars. These bodies are extremely small; some
of them probably containing less matter than the largest mountains on
the earth's surface. More than ninety members of the group are known at
present, and the number is annually increasing.

JUPITER, the first planet exterior to the asteroids, is nearly five
hundred millions of miles from the sun, and revolves round him in a
little less than twelve years. This planet is ninety thousand miles in
diameter and contains more than twice as much matter as all the other
planets, primary and secondary, put together. Jupiter is attended by
four moons or satellites.

SATURN is the seventh planet in the order of distance--counting the
asteroids as one. Its orbit is about four hundred millions of miles
beyond that of Jupiter. This planet is attended by eight satellites,
and is surrounded by three broad, flat rings. Saturn is seventy-six
thousand miles in diameter, and its mass or quantity of matter is more
than twice that of all the other planets except Jupiter.

URANUS is at double the distance of Saturn, or nineteen times that
of the earth. Its diameter is about thirty-five thousand miles, and
its period of revolution, eighty-four years. It is attended by four
satellites.

NEPTUNE is the most remote known member of the system; its distance
being nearly three thousand millions of miles. It is somewhat larger
than Uranus; has certainly one satellite, and probably several more.
Its period is about one hundred and sixty-five years. A cannon-ball
flying at the rate of five hundred miles per hour would not reach the
orbit of Neptune from the sun in less than six hundred and eighty years.

These planets all move round the sun in the same direction--from west
to east. Their motions are nearly circular, and also nearly in the same
plane. Their orbits, except that of Neptune, are represented in the
frontispiece. It is proper to remark, however, that all representations
of the solar system by maps and planetariums must give an exceedingly
erroneous view either of the magnitudes or distances of its various
members. If the earth, for instance, be denoted by a ball half an
inch in diameter, the diameter of the sun, according to the same
scale (sixteen thousand miles to the inch), will be between four and
five feet; that of the earth's orbit, about one thousand feet; while
that of Neptune's orbit will be nearly six miles. To give an accurate
representation of the solar system at a single view is therefore
plainly impracticable.

COMETS.--The number of comets belonging to our system is unknown. The
appearance of more than seven hundred has been recorded, and of this
number, the elements of about two hundred have been computed. They move
in very eccentric orbits--some, perhaps, in parabolas or hyperbolas.

THE ZODIACAL LIGHT is a term first applied by Dominic Cassini, in
1683, to a faint nebulous aurora, somewhat resembling the milky-way,
apparently of a conical or lenticular form, having its base toward
the sun, and its axis nearly in the direction of the ecliptic. The
most favorable time for observing it is when its axis is most nearly
perpendicular to the horizon. This, in our latitudes, occurs in March
for the evening, and in October for the morning. The angular distance
of its vertex from the sun is frequently seventy or eighty degrees,
while sometimes, though rarely (except within the tropics), it exceeds
even one hundred degrees.

The zodiacal light is probably identical with the meteor called
_trabes_ by _Pliny_ and _Seneca_. It was noticed in the latter part
of the sixteenth century by Tycho Brahé, who "considered it to be an
abnormal spring-evening twilight." It was described by Descartes
about the year 1630, and again by Childrey in 1661. The first accurate
description of the phenomenon was given, however, by Cassini. This
astronomer supposed the appearance to be produced by the blended
light of an innumerable multitude of extremely small planetary bodies
revolving in a ring about the sun. The appearance of the phenomenon as
seen in this country is represented in Fig. 2.

[Illustration: Fig. 2.]

For general readers it may not be improper to premise the following
explanations:

Meteors are of two kinds, _cosmical_ and _terrestrial_: the former
traverse the interplanetary spaces; the latter originate in the earth's
atmosphere.

_Bolides_ is a general name for meteoric fire-balls of greater
magnitude than shooting-stars.

The _period_ of a planet, comet, or meteor is the time which it
occupies in completing one orbital revolution.

The motion of a heavenly body is said to be _direct_ when it is from
west to east; and _retrograde_ when it is from east to west.

_Encke's Hypothesis of a Resisting Medium._--The time occupied by
Encke's comet in completing its revolution about the sun is becoming
less and less at each successive return. Professor Encke explains
this fact by supposing the interplanetary spaces to be filled with an
extremely rare fluid, the resistance of which to the cometary motion
produces the observed contraction of the orbit.



METEORIC ASTRONOMY.



CHAPTER I.

SHOOTING-STARS.


I. The Meteors of November 12th-14th.

Although shooting-stars have doubtless been observed in all ages of the
world, they have never, until recently, attracted the special attention
of scientific men. The first exact observations of the phenomena were
undertaken, about the close of the last century, by Messrs. Brandes and
Benzenberg. The importance, however, of this new department of research
was not generally recognized till after the brilliant meteoric display
of November 13th, 1833. This shower of fire can never be forgotten
by those who witnessed it.[1] The display was observed from the West
Indies to British America, and from 60° to 100° west longitude from
Greenwich. Captain Hammond, of the ship Restitution, had just arrived
at Salem, Massachusetts, where he observed the phenomenon from midnight
till daylight. He noticed with astonishment that precisely one year
before, viz., on the 13th of November, 1832, he had observed a similar
appearance (although the meteors were less numerous) at Mocha, in
Arabia. It was soon found, moreover, as a further and most remarkable
coincidence, that an extraordinary fall of meteors had been witnessed
on the 12th of November, 1799. This was seen and described by Andrew
Ellicott, Esq., who was then at sea near Cape Florida. It was also
observed in Cumana, South America, by Humboldt, who states that it
was "simultaneously seen in the new continent, from the equator to
New Herrnhut, in Greenland (lat. 64° 14´), and between 46° and 82°
longitude."

This wonderful correspondence of dates excited a very lively interest
throughout the scientific world. It was inferred that a recurrence
of the phenomenon might be expected, and accordingly arrangements
were made for systematic observations on the 12th, 13th, and 14th of
November. The periodicity of the shower was thus, in a very short
time, placed wholly beyond question. The examination of old historical
records led to the discovery of at least 12 appearances of the November
shower previous to the great fall of 1833. The descriptions of these
phenomena will be found collected in an interesting article by Prof.
H. A. Newton, in the _American Journal of Science and Arts_, for May,
1864. They occurred in the years 902, 931, 934, 1002, 1101, 1202,
1366, 1533, 1602, 1698, 1799, and 1832. Besides these 12 enumerated by
Professor Newton as "the predecessors of the great exhibition on the
morning of November 13th, 1833," we find 6 others, less distinctly
marked, in the catalogue of M. Quetelet.[2] These were in the years
1787, 1818, 1822, 1823, 1828, and 1831. From 1883 to 1849, inclusive,
Quetelet's catalogue indicates 11 partial returns of the November
shower; making in all, up to the latter date, 29. In 1835, November
13th, a straw roof was set on fire by a meteoric fire-ball, in the
department de l'Aine, France. On the 12th of November, 1837, "at 8
o'clock in the evening, the attention of observers in various parts
of Great Britain was directed to a bright luminous body, apparently
proceeding from the North, which, after making a rapid descent, in the
manner of a rocket, suddenly burst, and scattering its particles into
various beautiful forms, vanished in the atmosphere. This was succeeded
by others all similar to the first, both in shape and the manner of its
ultimate disappearance. The whole display terminated at ten o'clock,
when dark clouds, which continued up till a late hour, overspread the
earth, preventing any further observations."--_Milner's Gallery of
Nature_, p. 142.

In 1838, November 12th-13th, meteors were observed in unusual numbers
at Vienna. One of extraordinary brilliancy, having an apparent
magnitude equal to that of the full moon, was seen near Cherburg.

On several other returns of the November epoch the number of meteors
observed has been greater than on ordinary nights; the distinctly
marked exhibitions, however, up to 1866, have all been enumerated.


THE SHOWER OF NOVEMBER 14, 1866.

The fact that all great displays of the November meteors have
taken place at intervals of thirty-three or thirty-four years, or
some multiple of that period, had led to a general expectation of
a brilliant shower in 1866. In this country, however, the public
curiosity was much disappointed. The numbers seen were greater than
on ordinary nights, but not such as would have attracted any special
attention. The greatest number recorded at any one station was seen at
New Haven, by Prof. Newton. On the night of the 12th, 694 were counted
in five hours and twenty minutes, and on the following night, 881
in five hours. This was about six times the ordinary number. A more
brilliant display was, however, witnessed in Europe. Meteors began
to appear in unusual frequency about eleven o'clock on the night of
the 13th, and continued to increase with great rapidity for more than
two hours; the maximum being reached a little after one o'clock. The
Edinburgh _Scotsman_, of November 14th, contains a highly interesting
description of the phenomenon as observed at that city. "Standing on
the Calton Hill, and looking westward," the editor remarks,--"with
the Observatory shutting out the lights of Prince's Street--it was
easy for the eye to delude the imagination into fancying some distant
enemy bombarding Edinburgh Castle from long range; and the occasional
cessation of the shower for a few seconds, only to break out again with
more numerous and more brilliant drops of fire, served to countenance
this fancy. Again, turning eastward, it was possible now and then to
catch broken glimpses of the train of one of the meteors through the
grim dark pillars of that ruin of most successful manufacture, the
National Monument; and in fact from no point in or out of the city was
it possible to watch the strange rain of stars, pervading as it did all
points of the heavens, without pleased interest, and a kindling of the
imagination, and often a touch of deeper feeling that bordered on awe.
The spectacle, of which the loftiest and most elaborate description
could but be at the best imperfect--which truly should have been seen
to be imagined--will not soon pass from the memories of those to whose
minds were last night presented the mysterious activities and boundless
fecundities of that universe of the heavens, the very unchangeableness
of whose beauty has to many made it monotonous and of no interest."

The appearance of the phenomenon, as witnessed at London, is minutely
described in the _Times_ of November 15th. The shower occurred chiefly
between the hours of twelve and two. About one o'clock a single
observer counted 200 in two minutes. The whole number seen at Greenwich
was 8485. The shower was also observed in different countries on the
continent.


_The Meteors of 1866 compared with those of former Displays._

The star shower of 1866 was much inferior to those of 1799 and
1833.[3] With these exceptions, however, it has, perhaps, been
scarcely surpassed during the last 500 years. Historians represent the
meteors of 902 as innumerable, and as moving like rain in all possible
directions.[4] The exhibition of 1202 was no less magnificent. The
stars, it is said, were seen to dash against each other like swarms of
locusts; the phenomenon lasting till daybreak.[5] The shower of 1366
is thus described in a Portuguese chronicle, quoted by Humboldt: "In
the year 1366, twenty-two days of the month of October being past,
three months before the death of the king, Dom Pedro (of Portugal),
there was in the heavens a movement of stars, such as men never before
saw or heard of. At midnight, and for some time after, all the stars
moved from the east to the west; and after being collected together,
they began to move, some in one direction, and others in another.
And afterward they fell from the sky in such numbers, and so thickly
together, that as they descended low in the air, they seemed large and
fiery, and the sky and the air seemed to be in flames, and even the
earth appeared as if ready to take fire. That portion of the sky where
there were no stars, seemed to be divided into many parts, and this
lasted for a long time."

The following is Humboldt's description of the shower of 1799, as
witnessed by himself and Bonpland, in Cumana, South America: "From half
after two, the most extraordinary luminous meteors were seen toward the
east.... Thousands of bolides and falling stars succeeded each other
during four hours. They filled a space in the sky extending from the
true east 30° toward the north and south. In an amplitude of 60° the
meteors were seen to rise above the horizon at E. N. E. and at E.,
describe arcs more or less extended, and fall toward the south, after
having followed the direction of the meridian. Some of them attained a
height of 40°, and all exceeded 25° or 30°.... Mr. Bonpland relates,
that from the beginning of the phenomenon there was not a space in
the firmament equal in extent to three diameters of the moon, that
was not filled at every instant with bolides and falling-stars....
The Guaiqueries in the Indian suburb came out and asserted that the
firework had begun at one o'clock.... The phenomenon ceased by degrees
after four o'clock, and the bolides and falling-stars became less
frequent; but we still distinguished some toward the northeast a
quarter of an hour after sunrise."


DISCUSSION OF THE PHENOMENA.

Since the memorable display of November 13th, 1833, the phenomena of
shooting-stars have been observed and discussed by Brandes, Benzenberg,
Olbers, Saigey, Heis, Olmsted, Herrick, Twining, Newton, Greg, and many
others. In the elaborate paper of Professor Olmsted, it was shown that
the meteors had their origin at a distance of more than 2000 miles
from the earth's surface; that their paths diverged from a common point
near the star _Gamma Leonis_; that in a number of instances they became
visible about 80 miles from the earth's surface; that their velocity
was comparable to that of the earth in its orbit; and that in some
cases their extinction occurred at an elevation of 30 miles. It was
inferred, moreover, that they consisted of combustible matter which
took fire and was consumed in passing through the atmosphere; that this
matter was derived from a nebulous body revolving round the sun in an
elliptical orbit, but little inclined to the plane of the ecliptic;
that its aphelion was near that point of the earth's orbit through
which we annually pass about the 13th of November--the perihelion being
a little within the orbit of Mercury; and finally that its period was
about one-half that of the earth. Dr. Olmsted subsequently modified his
theory, having been led by further observations to regard the zodiacal
light as the nebulous body from which the shooting-stars are derived.
The latter hypothesis was also adopted by the celebrated Biot.

The fact that the position of the radiant point does not change with
the earth's rotation, places the cosmical origin of the meteors wholly
beyond question. The theory of a closed ring of nebulous matter
revolving round the sun in an elliptical orbit which intersects that
of the earth, affords a simple and satisfactory explanation of the
phenomena. This theory was adopted by Humboldt, Arago, and others,
shortly after the occurrence of the meteoric shower of 1833. That the
body which furnishes the material of these meteors moves in a closed
or elliptical orbit is evident from the periodicity of the shower. It
is also manifest from the partial recurrence of the phenomenon from
year to year, that the matter is diffused around the orbit; while the
extraordinary falls of 1833, 1799, 1366, and 1202, prove the diffusion
to be far from uniform.


ELEMENTS OF THE ORBIT.

Future observations, it may be hoped, will ultimately lead to an
accurate determination of the elements of this ring: many years,
however, will probably elapse before all the circumstances of its
motion can be satisfactorily known. Professor Newton, of Yale College,
has led the way in an able discussion of the observations.[6] He has
shown that the different parts of the ring are, in all probability, of
very unequal density; that the motion is retrograde; and that the time,
during which the meteors complete a revolution about the sun, must be
limited to one of five accurately determined periods, viz.: 180·05
days, 185·54 days, 354·62 days, 376·5 days, or 33·25 years. He makes
the inclination of the ring to the ecliptic about 17°. The five periods
specified, he remarks, "are not all equally probable. Some of the
members of the group which visited us last November [1863] gave us the
means of locating approximately the central point of the region from
which the paths diverge. Mr. G. A. Nolen has, by graphical processes
specially devised for the purpose, found its longitude to be 142°, and
its latitude 8° 30´. This longitude is very nearly that of the point
in the ecliptic toward which the earth is moving. Hence the point
from which the absolute motion of the bodies is directed (being in a
great circle through the other two points) has the same longitude. The
absolute motion of each meteor, then, is directed very nearly at right
angles to a line from it to the sun, the deviation being probably not
more than two or three degrees.

"Now, if in one year the group make 2 ± 1/33·25 revolutions, there is
only a small portion of the orbit near the aphelion which fulfills the
above condition. In like manner, if the periodic time is 33·25 years,
only a small portion of the orbit near the perihelion fulfills it.
On the other hand, if the annual motion is 1 ± 1/33·25 revolutions,
the required condition is answered through a large part of the orbit.
Inasmuch as no reason appears why the earth should meet a group near
its apsides rather than elsewhere, we must regard it as more probable
that the group makes in one year either 1 + 1/33·25, or 1 - 1/33·25
revolutions."

Professor Newton concludes that the third of the above-mentioned
periods, viz., 354·62 days, combines the greatest amount of probability
of being the true one. We grant the force of the reasons assigned for
its adoption. At least one consideration, however, in favor of the
long period of 33·25 years is by no means destitute of weight: of
nearly 100 known bodies which revolve about the sun in orbits of small
eccentricity, not one has a retrograde motion. Now if this striking
fact has resulted from a general cause, how shall we account for the
backward motion of a meteoric ring, in an orbit almost circular, and
but little inclined to the plane of the ecliptic? In such a case, is
not the preponderance of probability in favor of the longer period?

A revolution in 33·25 years corresponds to an ellipse whose major axis
is 20·6. Consequently the aphelion distance would be somewhat greater
than the mean distance of Uranus. It may also be worthy of note, that
five periods of the ring would be very nearly equal to two of Uranus.

The _Monthly Notices of the Royal Astronomical Society_ for December,
1866, and January, 1867, contain numerous articles on the star shower
of November 13th-14th, 1866. Sir John Herschel carefully observed the
phenomena, and his conclusions in regard to the orbit are confirmatory
of those of Professor Newton. "We are constrained to conclude," he
remarks, "that the true line of direction, in space of each meteor's
flight, lay in a plane at right angles to the earth's radius vector at
the moment; and that therefore, except in the improbable assumption
that the meteor was at that moment _in perihelio_ or _in aphelio_, its
orbit would not deviate greatly from the circular form." The question
is one to be decided by observation, and the only meteor whose track
and time of flight seem to have been well observed, is that described
by Professor Newton in _Silliman's Journal_ for January, 1867, p. 86.
The velocity in this case, if the estimated time of flight was nearly
correct, was _inconsistent with the theory of a circular orbit_.

It is also worthy of notice that Dr. Oppolzer's elements of the first
comet of 1866 resemble, in a remarkable manner, those of the meteoric
ring, supposing the latter to have a period of about 33-1/4 years.
Schiaparelli's elements of the November ring, and Oppolzer's elements
of the comet of 1866, are as follows:

                                    November    Comet of
                                    Meteors.      1866.

    Longitude of perihelion         56° 25´      60° 28´
    Longitude of ascending node.   231  28      231  26
    Inclination                     17  44       17  18
    Perihelion distance             0·9873       0·9765
    Eccentricity                    0·9046       0·9054
    Semi-axis major                10·3400      10·3240
    Period, in years               33·2500      33·1760
    Motion                        Retrograde.  Retrograde.

It seems very improbable that these coincidences should be accidental.
Leverrier and other astronomers have found elements of the meteoric
orbit agreeing closely with those given by Schiaparelli. Should the
identity of the orbits be fully confirmed, it will follow that the
comet of 1866 _is a very large meteor_ of the November stream.

The researches of Professor C. Bruhns, of Leipzig, in regard to this
group of meteors afford a probable explanation of the division of
Biela's comet--a phenomenon which has greatly perplexed astronomers for
the last twenty years. Adopting the period of 33-1/4 years, Professor
Bruhns finds that the comet passed extremely near, and probably
_through_ the meteoric ring near the last of December, 1845. It is easy
to perceive that such a collision might produce the separation soon
afterward observed.

As the comet of Biela makes three revolutions in twenty years, it was
again at this intersection, or approximate intersection of orbits about
the end of 1865. But although the comet's position, with respect to
the earth, was the same as in 1845-6, and although astronomers watched
eagerly for its appearance, their search was unsuccessful. In short,
_the comet is lost_. The denser portion of the meteoric stream was then
approaching its perihelion. A portion of the arc had even passed that
point, as a meteoric shower was observed at Greenwich on the 13th of
November, 1865.[7] The motion of the meteoric stream is retrograde;
that of the comet, direct. Did the latter plunge into the former, and
was its non appearance the result of such collision and entanglement?

[Illustration: Fig. 3.

_Probable Orbit of the November Meteors._]



CHAPTER II.

OTHER METEORIC RINGS.


II. The Meteors of August 6th-11th.

Muschenbroek, in his _Introduction to Natural Philosophy_, published
in 1762, called attention to the fact that shooting-stars are more
abundant in August than in any other part of the year. The annual
periodicity of the maximum on the 9th or 10th of the month was
first shown, however, by Quetelet, shortly after the discovery of
the yearly return of the November phenomenon. Since that time an
extraordinary number of meteors has been regularly observed, both
in Europe and America, from the 7th to the 11th of the month; the
greatest number being generally seen on the 10th. In 1839, Edward Heis,
of Aix-la-Chapelle, saw 160 meteors in one hour on the night of the
10th. In 1842, he saw 34 in ten minutes at the time of the maximum. In
1861, on the night of the 10th, four observers, watching together at
New Haven, saw in three hours--from ten to one o'clock--289 meteors.
On the same night, at Natick, Massachusetts, two observers saw 397
in about seven hours. At London, Mercer County, Pennsylvania, on the
night of August 9th, 1866, Samuel S. Gilson, Esq., watching alone, saw
72 meteors in forty minutes, and, with an assistant, 117 in one hour
and fifteen minutes. Generally, the number observed per hour, at the
time of the August maximum, is about nine times as great as on ordinary
nights. Like the November meteors, they have a common "radiant;" that
is, their tracks, when produced backward, meet, or nearly meet, in a
particular point in the constellation Perseus.

Of the 315 meteoric displays given in Quetelet's "Catalogue des
principales apparitions d'étoiles filantes," 63 seem to have been
derived from the August ring. The first 11 of these, with one
exception, were observed in China during the last days of July, as
follows:

     1   A.D. 811, July 25th.
     2        820,  "   25th-30th.
     3        824,  "   26th-28th.
     4        830,  "   26th.
     5        833,  "   27th.
     6        835,  "   26th.
     7        841,  "   25th-30th.
     8        924,  "   27th-30th.
     9        925,  "   27th-30th.
    10        926,  "   27th-30th.
    11        933,  "   25th-30th.

The next dates are 1243, August 2d, and 1451, August 7th. A comparison
of these dates indicates a forward motion of the node of the ring along
the ecliptic. This was pointed out several years since by Boguslawski.
A similar motion of the node has also been found in the case of the
November ring. That these points should be stationary is, indeed,
altogether improbable. The nodes of all the planetary orbits, it is
well known, have a secular variation.

On the evening of August 10th, 1861, at about 11h. 30m., a meteor
was seen by Mr. E. C. Herrick and Prof. A. C. Twining, at New
Haven, Connecticut, which "was much more splendid than Venus, and
left a train of sparks which remained luminous for twenty seconds
after the meteor disappeared." The same meteor was also accurately
observed at Burlington, New Jersey, by Mr. Benjamin V. Marsh. It was
"conformable,"--that is, its track produced backward passed through the
common radiant--and it was undoubtedly a member of the August group.
The observations were discussed by Professor H. A. Newton, of Yale
College, who deduced from them the following approximate elements of
the ring:[8]

    Semi-axis major        0·84
    Eccentricity           0·28
    Perihelion distance    0·60
    Inclination             84°
    Period                  281 days.
    Motion, retrograde.

The earth moving at the rate of 68,000 miles per hour, is at least five
days in passing entirely through the ring. This gives a thickness of
more than 8,000,000 miles.

The result of Professor Newton's researches on the orbit of this ring,
though undertaken with inadequate data, and hence, in some respects,
probably far from correct, is nevertheless highly interesting as being
the first attempt to determine the orbit of shooting-stars. More recent
investigations have shown a remarkable resemblance between the elements
of these meteors and those of the third comet of 1862. The former, by
Schiaparelli, and the latter, by Oppolzer, are as follows:


                          Meteors of August 10th.   Comet III., 1862.

    Longitude of perihelion   343° 38´                344° 41
    Ascending node            138  16                 137  27
    Inclination                63   3                  66  25
    Perihelion distance        0·9643                  0·9626
    Period                    105 years(?).           123 years(?).
    Motion                    Retrograde.             Retrograde.

This similarity is too great to be accidental. _The August meteors and
the third comet of 1862 probably belong to the same ring._


III. The Meteors of April 18th-26th.

The following dates of the April meteoric showers are extracted from
Quetelet's table previously referred to:

     1    A.D. 401, April 9th.
     2         538,   "   7th.
     3         839,   "  17th.
     4         927,   "  17th.
     5         934,   "  18th.
     6        1009,   "  16th.
     7        1094,   "  10th.
     8        1096,   "  10th.
     9        1122,   "  11th.
    10        1123,   "  11th.
    11        1803,   "  20th.
    12        1838,   "  20th.
    13        1841,   "  19th.
    14        1850,   "  11th-17th.

The display of 401 was witnessed in China, and is described as "very
remarkable." That of 1803 was best observed in Virginia, and was at its
maximum between one and three o'clock. The alarm of fire had called
many of the inhabitants of Richmond from their houses, so that the
phenomenon was generally witnessed. The meteors "seemed to fall from
every point in the heavens, in such numbers as to resemble a shower of
sky-rockets." Some were of extraordinary magnitude. "One in particular,
appeared to fall from the zenith, of the apparent size of a ball 18
inches in diameter, that lighted the whole hemisphere for several
seconds."

The probability that the meteoric falls about the 20th of April are
derived from a ring which intersects the earth's orbit, was first
suggested by Arago, in 1836. The preceding list indicates a forward
motion of the node. The radiant, according to Mr. Greg, is about
_Corona_. The number of meteors observed in 1838, 1841, and 1850, was
not very extraordinary. Recent observations indicate April 9th-12th as
another epoch. The radiant is in Virgo.


IV. The Meteors of December 6th-13th.

On the 13th of December, 1795, a large meteoric stone fell in England.
On the night, between the 6th and 7th of December, 1798, Professor
Brandes, then a student in Göttingen, saw 2000 shooting-stars. On
the 11th of the month, 1836, a fall of meteoric stones, described by
Humboldt as "enormous," occurred near the village of Macao, in Brazil.
During the last few years unusual numbers of shooting-stars have been
noticed by different observers from the 10th to the 13th; the maximum
occurring about the 11th. From A.D. 848, December 2d, to 1847, December
8th-10th, we find 14 star showers in Quetelet's catalogue, derived,
probably, from this meteoric stream. As in other cases, the dates
seem to show a progressive motion of the node. The position of the
radiant, as determined by Benjamin V. Marsh, Esq., of Philadelphia,
from observations in 1861 and 1862, and also by R. P. Greg, Esq., of
Manchester, England, is at a point midway between Castor and Pollux.


V. The Meteors of January 2d-3d.

About the middle of the present century, Mr. Julius Schmidt, of Bonn,
a distinguished and accurate observer, designated the 2d of January as
a meteoric epoch; characterizing it, however, as "probably somewhat
doubtful." Recent observations, especially those of R. P. Greg, Esq.,
have fully confirmed it. The meteors for several hours are said to be
as numerous as at the August maximum. The radiant is near the star
_Beta_ of the constellation Böotes.

Quetelet's list contains at least five exhibitions which belong to this
epoch. Two or three others may also be referred to it with more or less
probability.

       *       *       *       *       *

Several other meteoric epochs have been indicated; some of which,
however, must yet be regarded as doubtful. In thirty years, from 1809
to 1839, 12 falls of bolides and meteoric stones occurred from the 27th
to the 29th of November. Such coincidences can hardly be accidental.
Unusual numbers of shooting-stars have also been seen about the 27th
of July; from the 15th to the 19th of October, and about the middle
of February. The radiant, for the last-mentioned epoch, is in _Leo
Minor_. The numbers observed in October are said to be at present
increasing. At least seven of the exhibitions in Quetelet's catalogue
are referable to this epoch. It is worthy of remark, moreover, that
three of the dates specified by Mr. Greg as _aerolite_ epochs are
coincident with those of shooting-stars; viz., February 15th-19th, July
26th, and December 13th. The whole number of exhibitions enumerated
in Quetelet's catalogue is 315. In eighty-two instances the day of
the month on which the phenomenon occurred is not specified. Nearly
two-thirds of the remainder, as we have seen, belong to established
epochs, and the periodicity of others will perhaps yet be discovered.
But reasons are not wanting for believing that our system is traversed
by numerous meteoric streams besides those which actually intersect the
earth's orbit. The asteroid region between Mars and Jupiter is probably
occupied by such an annulus. The number of these asteroids increases
as their magnitudes diminish; and this doubtless continues to be the
case far below the limit of telescopic discovery. The zodiacal light
is probably a dense meteoric ring, or rather, perhaps, a number of
rings. We speak of it as _dense_ in comparison with others, which are
invisible except by the ignition of their particles in passing through
the atmosphere. From a discussion of the motions of the perihelia of
Mercury and Mars, Leverrier has inferred the existence of two rings of
minute asteroids; one within the orbit of Mercury, whose mass is nearly
equal to that of Mercury himself; the other at the mean distance of the
earth, whose mass cannot _exceed_ the tenth part of the mass of the
earth.

Within the last few years a distinguished European savant, Buys-Ballot,
of Utrecht, has discovered a short period of variation in the amount
of solar heat received by the earth: the time from one maximum to
another exceeding the period of the sun's apparent rotation by about
twelve hours. The variation cannot therefore be due to any inequality
in the heating power of the different portions of the sun's surface.
The discoverer has suggested that it may be produced by a meteoric
ring, whose period slightly exceeds that of the sun's rotation. Such
a zone might influence our temperature by partially intercepting the
solar heat.


GENERAL REMARKS.

1. The average number of shooting-stars seen in a clear, moonless
night by a single observer, is about 8 per hour. _One_ observer,
however, sees only about one-fourth of those visible from his point of
observation. About 30 per hour might therefore be seen by watching the
entire hemisphere. In other words, 720 shooting-stars per day could be
seen by the naked eye at any one point of the earth's surface, did the
sun, moon, and clouds permit.

2. The mean altitude of shooting-stars above the earth's surface is
about 60 miles.

3. The number visible over the whole earth is about 10,460 times the
number to be seen at any one point. Hence the average number of those
daily entering the atmosphere and having sufficient magnitude to be
seen by the naked eye, is about 7,532,600.

4. The observations of Pape and Winnecke indicate that the number of
meteors visible through the telescope, employed by the latter, is about
53 times the number visible to the naked eye, or about 400,000,000
per day.[9] This is two per day, or 73,000 per century, for every
square mile of the earth's surface. By increasing the optical power,
this number would probably be indefinitely increased. At special
times, moreover, such as the epochs of the great meteoric showers,
the addition of foreign matter to our atmosphere is much greater than
ordinary. It becomes, therefore, an interesting question whether
sensible changes may not thus be produced in the atmosphere of our
planet.

5. In August, 1863, 20 shooting-stars were doubly observed in England;
that is, they were seen at two different stations. The average weight
of these meteors, estimated--in accordance with the mechanical theory
of heat--from the quantity of light emitted, was a little more than two
ounces.

6. A meteoric mass exterior to the atmosphere, and consequently
non-luminous, was observed on the evening of October 4th, 1864, by
Edward Heis, a distinguished European astronomer. It entered the field
of view as he was observing the milky way, and he was enabled to follow
it over 11 or 12 degrees of its path. It eclipsed, while in view, a
number of the fixed stars.



CHAPTER III.

AEROLITES.


It is now well known that much greater variety obtains in the structure
of the solar system than was formerly supposed. This is true, not only
in regard to the magnitudes and densities of the bodies composing it,
but also in respect to the forms of their orbits. The whole number
of planets, primary and secondary, known to the immortal author of
the _Mecanique Celeste_, was only 29. This number has been more than
quadrupled in the last quarter of a century. In Laplace's view,
moreover, all comets were strangers within the solar domain, having
entered it from without. It is now believed that a large proportion
originated in the system and belong properly to it.

The gradation of planetary magnitudes, omitting such bodies as differ
but little from those given, is presented at one view in the following
table:

    Name.                             Diameter in miles.

    Jupiter                                 90,000
    Uranus                                  35,000
    The Earth                                7,926
    Mercury                                  3,000
    The Moon                                 2,160
    Rhea, Saturn's 5th satellite             1,200
    Dione   "      4th     "                   500
    Vesta[10]                                  260
    Juno                                       104
    Melpomene                                   52
    Polyhymnia                                  35
    Isis                                        25
    Atalanta                                    20
    Hestia                                      15

The diminution doubtless continues indefinitely below the present limit
of optical power. If, however, the orbits have small eccentricity, such
asteroids could not become known to us unless their mean distances were
nearly the same with that of the earth. But from the following table it
will be seen that the variety is no less distinctly marked in the forms
of the orbits:

    Name.                                Eccentricity.

    Venus                                  0·00683
    The Earth                              0·01677
    Jupiter                                0·04824
    Metis                                  0·12410
    Mercury                                0·20562
    Pallas                                 0·24000
    Polyhymnia                             0·33820
    Faye's comet                           0·55660
    D'Arrest's "                           0·66090
    Biela's    "                           0·75580
    Encke's    "                           0·84670
    Halley's   "                           0·96740
    Fourth comet of 1857                   0·98140
    Fifth comet of 1858 (Donati's)         0·99620
    Third comet of 1827                    0·99927

Were the eccentricities of the nearest asteroids equal to that of
Faye's comet, they would in perihelion intersect the earth's orbit.
Now, in the case of both asteroids and comets, the smallest are the
most numerous; and as this doubtless continues below the limit of
telescopic discovery, the earth ought to encounter such bodies in
its annual motion. _It actually does so._ The number of _cometoids_
thus encountered in the form of _meteoric stones_, _fire-balls_,
and _shooting-stars_ in the course of a single year amounts to many
millions. The extremely minute, and such as consist of matter in the
gaseous form, are consumed or dissipated in the upper regions of the
atmosphere. No deposit from ordinary shooting-stars has ever been known
to reach the earth's surface. But there is probably great variety
in the physical constitution of the bodies encountered; and though
comparatively few contain a sufficient amount of matter in the solid
form to reach the surface of our planet, scarcely a year passes without
the fall of meteoric stones in some part of the earth, either singly or
in clusters. Now, when we consider how small a proportion of the whole
number are probably observed, it is obvious that the actual occurrence
of the phenomenon can be by no means rare.[11]

Although numerous instances of the fall of aerolites had been
recorded, some of them apparently well authenticated, the occurrence
long appeared too marvelous and improbable to gain credence with
scientific men. Such a shower of rocky fragments occurred, however,
on the 26th of April, 1803, at L'Aigle, in France, as forever to
dissipate all doubt on the subject. At one o'clock P.M., the heavens
being almost cloudless, a tremendous noise, like that of thunder, was
heard, and at the same time an immense fire-ball was seen moving with
great rapidity through the atmosphere. This was followed by a violent
explosion which lasted several minutes, and which was heard not only at
L'Aigle, but in every direction around it to the distance of seventy
miles. Immediately after a great number of meteoric stones fell to the
earth, generally penetrating to some distance beneath the surface. The
largest of these fragments weighed 17-1/2 pounds. This occurrence very
naturally excited great attention. M. Biot, under the authority of the
government, repaired to L'Aigle, collected the various facts in regard
to the phenomenon, took the depositions of witnesses, etc., and finally
embraced the results of his investigations in an elaborate memoir.

It would not comport with the design of the present treatise to give
an extended list of these phenomena. The following account, however,
includes the most important instances of the fall of aerolites, and
also of the displays of meteoric fire-balls.

1. According to Livy a number of meteoric stones fell on the Alban
Hill, near Rome, about the year 654 B.C. This is the most ancient fall
of aerolites on record.

2. 468 B.C., about the year in which Socrates was born. A mass of rock,
described as "of the size of two millstones," fell at Ægos Potamos, in
Thrace. An attempt to rediscover this meteoric mass, so celebrated in
antiquity, was recently made, but without success. Notwithstanding
this failure, Humboldt expressed the hope that, as such a body would be
difficult to destroy, it may yet be found, "since the region in which
it fell is now become so easy of access to European travelers."

3. 921 A.D. An immense aerolite fell into the river (a branch of the
Tiber) at Narni, in Italy. It projected three or four feet above the
surface of the water.

4. 1492, November 7th. An aerolite, weighing two hundred and
seventy-six pounds, fell at Ensisheim, in Alsace, penetrating the earth
to the depth of three feet. This stone, or the greater portion of it,
may still be seen at Ensisheim.

5. 1511, September 14th. At noon an almost total darkening of the
heavens occurred at Crema. "During this midnight gloom," says a writer
of that period, "unheard-of thunders, mingled with awful lightnings,
resounded through the heavens. * * * On the plain of Crema, where never
before was seen a stone the size of an egg, there fell pieces of rock
of enormous dimensions and of immense weight. It is said that ten of
these were found weighing a hundred pounds each." A monk was struck
dead at Crema by one of these rocky fragments. This terrific meteoric
display is said to have lasted two hours, and 1200 aerolites were
subsequently found.

6. 1637, November 29th. A stone, weighing fifty-four pounds, fell on
Mount Vaison, in Provence.

7. 1650, March 30th. A Franciscan monk was killed at Milan by the fall
of a meteoric stone.

8. 1674. Two Swedish sailors were killed on ship-board by the fall of
an aerolite.

9. 1686, July 19th. An extraordinary fire-ball was seen in England;
its motion being opposite to that of the earth in its orbit. Halley
pronounced this meteor a cosmical body. (See Philos. Transact., vol.
xxix.)

10. 1706, June 7th. A stone weighing seventy-two pounds fell at
Larissa, in Macedonia.

11. 1719, March 19th. Another great meteor was seen in England. Its
explosion occurred at an elevation of 69 miles. Notwithstanding its
height, however, the report was like that of a broadside, and so great
was the concussion that windows and doors were violently shaken.

12. 1751, May 26th. Two meteoric masses, consisting almost wholly of
iron, fell near Agram, the capital of Croatia. The larger fragment,
which weighs seventy-two pounds, is now in Vienna.

13. 1756. The concussion produced by a meteoric explosion threw down
chimneys at Aix, in Provence, and was mistaken for an earthquake.

14. 1771, July 17th. A large meteor exploded near Paris, at an
elevation of 25 miles.

15. 1783, August 18th. A fire-ball of extraordinary magnitude was seen
in Scotland, England, and France. It produced a rumbling sound like
distant thunder, although its elevation above the earth's surface was
50 miles at the time of its explosion. The velocity of its motion was
equal to that of the earth in its orbit, and its diameter, according to
Sir Charles Blagden, was about half a mile.

16. 1790, July 24th. Between nine and ten o'clock at night a very large
igneous meteor was seen near Bourdeaux, France. Over Barbotan a loud
explosion was heard, which was followed by a shower of meteoric stones
of various magnitudes.

17. 1794, July. A fall of about a dozen aerolites occurred at Sienna,
Tuscany.

18. 1795, December 13th. A large meteoric stone fell near Wold Cottage,
in Yorkshire, England. The following account of the phenomenon is
taken from Milner's _Gallery of Nature_, p. 134: "Several persons
heard the report of an explosion in the air, followed by a hissing
sound; and afterward felt a shock, as if a heavy body had fallen to the
ground at a little distance from them. One of these, a plowman, saw
a huge stone falling toward the earth, eight or nine yards from the
place where he stood. It threw up the mould on every side; and after
penetrating through the soil, lodged some inches deep in solid chalk
rock. Upon being raised, the stone was found to weigh fifty-six pounds.
It fell in the afternoon of a mild but hazy day, during which there
was no thunder or lightning; and the noise of the explosion was heard
through a considerable district."

19. 1796, February 19th. A stone of ten pounds' weight fell in Portugal.

20. 1798, March 12th. A stone weighing twenty pounds fell at Sules,
near Ville Franche.

21. 1798, March 17th. An aerolite weighing about twenty pounds fell at
Sale, Department of the Rhone.

22. 1798, December 19th. A shower of meteoric stones fell at Benares,
in the East Indies. An interesting account of the phenomenon was given
by J. Lloyd Williams, F.R.S., then a resident in Bengal. The sky had
been perfectly clear for several days. At eight o'clock in the evening
a large meteor appeared, which was attended with a loud rumbling
noise. Immediately after the explosion a sound was heard like that of
heavy bodies falling in the neighborhood. Next morning the fresh earth
was found turned up in many places, and aerolites of various sizes were
discovered beneath the surface.

23. 1803, April 26th. The shower at L'Aigle, previously described.

24. 1807, December 14th. A large meteor exploded over Weston,
Connecticut. The height, direction, velocity, and magnitude of this
body were ably discussed by Dr. Bowditch in a memoir communicated
to the American Academy of Arts and Sciences in 1815. The following
condensed statement of the principal facts, embodied in Dr. Bowditch's
paper, is extracted from the _People's Magazine_ for January 25th, 1834:

"The meteor of 1807 was observed about a quarter-past six on Monday
morning. The day had just dawned, and there was little light except
from the moon, which was just setting. It seemed to be half the
diameter of the full moon; and passed, like a globe of fire, across
the northern margin of the sky. It passed behind some clouds, and when
it came out it flashed like heat lightning. It had a train of light,
and appeared like a burning fire-brand carried against the wind. It
continued in sight about half a minute, and, in about an equal space
after it faded, three loud and distinct reports, like those of a
four-pounder near at hand, were heard. Then followed a quick succession
of smaller reports, seeming like what soldiers call a running fire. The
appearance of the meteor was as if it took three successive throes, or
leaps, and at each explosion a rushing of stones was heard through the
air, some of which struck the ground with a heavy fall.

"The first fall was in the town of Huntington, near the house of Mr.
Merwin Burr. He was standing in the road, in front of his house, when
the stone fell, and struck a rock of granite about fifty feet from him,
with a loud noise. The rock was stained a dark-red color, and the stone
was principally shivered into very small fragments, which were thrown
around to a distance of twenty feet. The largest piece was about the
size of a goose egg, and was still warm.

"The stones of the second explosion fell about five miles distant, near
Mr. William Prince's residence, in Weston. He and his family were in
bed when they heard the explosion, and also heard a heavy body fall to
the earth. They afterward found a hole in the earth, about twenty-five
feet from the house, like a newly dug post-hole, about one foot in
diameter, and two feet deep, in which they found a meteoric stone
buried, which weighed thirty-five pounds. Another mass fell half a mile
distant, upon a rock, which it split in two, and was itself shivered to
pieces. Another piece, weighing thirteen pounds, fell a half a mile to
the northeast, into a plowed field.

"At the last explosion, a mass of stone fell in a field belonging to
Mr. Elijah Seely, about thirty rods from the house. This stone falling
on a ledge, was shivered to pieces. It plowed up a large portion of the
ground, and scattered the earth and stones to the distance of fifty or
a hundred feet. Some cattle that were near were very much frightened,
and jumped into an inclosure. It was concluded that this last stone,
before being broken, must have weighed about two hundred pounds. These
stones were all of a similar nature, and different from any commonly
found on this globe. When first found, they were easily reduced to
powder by the fingers, but by exposure to the air they gradually
hardened."

25. 1859, November 15th. Between nine and ten o'clock in the morning,
an extraordinary meteor was seen in several of the New England States,
New York, New Jersey, the District of Columbia, and Virginia. The
apparent diameter of the head was nearly equal to that of the sun,
and it had a train, notwithstanding the bright sunshine, several
degrees in length. Its disappearance on the coast of the Atlantic was
followed by a series of the most terrific explosions. It is believed
to have descended into the water, probably into Delaware Bay. A highly
interesting account of this meteor, by Prof. Loomis, may be found in
the _American Journal of Science and Arts_ for January, 1860.

26. 1860, May 1st. About twenty minutes before one o'clock P.M.,
a shower of meteoric stones--one of the most extraordinary on
record--fell in the S. W. corner of Guernsey County, Ohio. Full
accounts of the phenomena are given in _Silliman's Journal_ for July,
1860, and January and July, 1861, by Professors E. B. Andrews, E.
W. Evans, J. L. Smith, and D. W. Johnson. From these interesting
papers we learn that the course of the meteor was about 40° west of
north. Its visible track was over Washington and Noble Counties, and
the prolongation of its projection, on the earth's surface, passes
directly through New Concord, in the S. E. corner of Muskingum County.
The height of the meteor, when seen, was about 40 miles, and its path
was nearly parallel with the earth's surface. The sky, at the time,
was, for the most part, covered with clouds over northwestern Ohio, so
that if any portion of the meteoric mass continued on its course, it
was invisible. The velocity of the meteor, in relation to the earth's
surface, was from 3 to 4 miles per second; and hence its absolute
velocity in the solar system was from 20 to 21 miles per second. This
would indicate an orbit of considerable eccentricity.

"At New Concord,[12] Muskingum County, where the meteoric stones fell,
and in the immediate neighborhood, there were many distinct and loud
reports heard. At New Concord there were first heard in the sky, a
little southeast of the zenith, a loud detonation, which was compared
to that of a cannon fired at the distance of half a mile. After an
interval of ten seconds another similar report. After two or three
seconds another, and so on with diminishing intervals. Twenty-three
distinct detonations were heard, after which the sounds became blended
together and were compared to the rattling fire of an awkward squad of
soldiers, and by others to the roar of a railway train. These sounds,
with their reverberations, are thought to have continued for two
minutes. The last sounds seemed to come from a point in the southeast
45° below the zenith. The result of this cannonading was the falling
of a large number of stony meteorites upon an area of about ten miles
long by three wide. The sky was cloudy, but some of the stones were
seen first as 'black specks,' then as 'black birds,' and finally
falling to the ground. A few were picked up within twenty or thirty
minutes. The warmest was no warmer than if it had lain on the ground
exposed to the sun's rays. They penetrated the earth from two to three
feet. The largest stone, which weighed one hundred and three pounds,
struck the earth at the foot of a large oak tree, and, after cutting
off two roots, one five inches in diameter, and grazing a third root,
it descended two feet ten inches into hard clay. This stone was found
resting under a root that was not cut off. This would seemingly imply
that it entered the earth obliquely."

Over thirty of the stones which fell were discovered, while doubtless
many, especially of the smaller, being deeply buried beneath the soil,
entirely escaped observation. The weight of the largest ten was four
hundred and eighteen pounds.

27. 1864, May 14th. Early in the evening a very large and brilliant
meteor was seen in France, from Paris to the Spanish border. At
Montauban, and in the vicinity, loud explosions were heard, and showers
of meteoric stones fell near the villages of Orgueil and Nohic. The
principal facts in regard to this meteor are the following:

    Elevation when first seen, over              55 miles.
        "     at the time of its explosion       20   "
    Inclination of its path to the horizon       20° or 25°
    Velocity per second, about                   20 miles,

or equal to that of the earth's orbital motion. "This example," says
Prof. Newton, "affords the strongest proof that the detonating and
stone-producing meteors are phenomena not essentially unlike."

The foregoing list contains but a small proportion even of those
meteoric stones the date of whose fall is known. But besides these,
other masses have been found so closely similar in structure to
aerolites whose descent has been observed, as to leave no doubt in
regard to their origin. One of these is a mass of iron and nickel,
weighing sixteen hundred and eighty pounds, found by the traveler
Pallas, in 1749, at Abakansk, in Siberia. This immense aerolite may be
seen in the Imperial Museum at St. Petersburg. On the plain of Otumpa,
in Buenos Ayres, is a meteoric mass 7-1/2 feet in length, partly buried
in the ground. Its estimated weight is thirty-three thousand six
hundred pounds. A specimen of this stone, weighing fourteen hundred
pounds, has been removed and deposited in one of the rooms of the
British Museum. A similar block, of meteoric origin, weighing twelve
or thirteen thousand pounds, was discovered some years since in the
Province of Bahia, in Brazil.

Some of the inferences derived from the examination of meteoric stones,
and the consideration of the phenomena attending their fall, are the
following:

1. R. P. Greg, Esq., of Manchester, England, who has made luminous
meteors a special study, has found that meteoric stone-falls occur
with greater frequency than usual on or about particular days. He
calls attention especially to five aerolite epochs, viz.: February
15th-19th; May 19th; July 26th; November 29th, and December 13th.

2. It is worthy of remark that no new elements have been found in
meteoric stones. Humboldt, in his _Cosmos_, called attention to this
interesting fact. "I would ask," he remarks, "why the elementary
substances that compose one group of cosmical bodies, or one planetary
system, may not in a great measure be identical? Why should we not
adopt this view, since we may conjecture that these planetary bodies,
like all the larger or smaller agglomerated masses revolving round
the sun, have been thrown off from the once far more expanded solar
atmosphere, and have been formed from vaporous rings describing their
orbits round the central body?"[13]

3. But while aerolites contain no elements but such as are found in
the earth's crust, the manner in which these elements are combined
and arranged is so peculiar that a skillful mineralogist will readily
distinguish them from terrestrial substances.

4. Of the eighteen or nineteen elements hitherto observed in meteoric
stones, iron is found in the greatest abundance. The specific gravities
vary from 1·94 to 7·901: the former being that of the stone of Alais,
the latter, that of the meteorite of Wayne County, Ohio, described by
Professor J. L. Smith in _Silliman's Journal_ for November, 1864, p.
385. In most cases, however, the specific gravity is about 3 or 4.

5. The contemplation of the heavenly bodies has often produced
in thoughtful minds an intense desire to know something of their
nature and physical constitution. This curiosity is gratified in the
examination of aerolites. To handle, weigh, inspect, and analyze
bodies that have wandered unnumbered ages through the planetary
spaces--perhaps approaching in their perihelia within a comparatively
short distance of the solar surface, and again receding in their
aphelia to the limits of the planetary system--must naturally excite a
train of pleasurable emotions.

6. It is highly probable that in pre-historic times, before the solar
system had reached its present stage of maturity, those chaotic
wanderers were more numerous in the vicinity of the earth's orbit than
in recent epochs. Even now the interior planets, Mercury and Venus,
appear to be moving through the masses of matter which constitute
the zodiacal light. It would seem probable, therefore, that they are
receiving from this source much greater accretions of matter than the
earth.

7. As Mercury's orbit is very eccentric, he is beyond his mean distance
during much more than half his period. Hence, probably, the greater
increments of meteoric matter are derived from such portions of the
zodiacal light as have a longer period than Mercury himself. If so, the
tendency would be to diminish slowly the planet's mean motion. Such a
lengthening of the period has been actually discovered.[14]



CHAPTER IV.

CONJECTURES IN REGARD TO METEORIC EPOCHS.


It is highly probable that aerolites and shooting-stars are derived
either from rings thrown off in the planes of the solar or planetary
equators, or from streams of nebulous matter drawn into the solar
system by the sun's attraction. Such annuli or streams would probably
each furnish an immense number of meteor-asteroids. If any rings
intersect the earth's orbit, our planet must encounter such masses as
happen at the same time to be passing the point of intersection. This
must be repeated _at the same epoch_ in different years; the frequency
of the encounter of course depending on the closeness and regularity
with which the masses are distributed around the ring. Accordingly it
has been found that not only the meteors of November 14th and of the
epochs named in Chapter II. have their respective radiants, but also
those of many other nights. Mr. Alexander S. Herschel, of Collingwood,
England, states that fifty-six such points of divergence are now well
established. We have mentioned in a previous chapter that Mr. Greg, of
Manchester, has specified several epochs at which fire-balls appear,
and meteoric stone-falls occur, with unusual frequency. The number
of these periods will probably be increased by future observations.
Perhaps the following facts may justify the designation of July
13th-14th as such an epoch:

1. On the 13th of July, 1797, a large fire-ball was seen in Göttingen.

2. On the 14th of July, 1801, a fire-ball was seen in Montgaillard.

3. On the 14th of July, 1845, a brilliant meteor was seen in London.

4. On the 13th of July, 1846, at about 9h. and 30m. P.M., a brilliant
fire-ball passed over Maryland and Pennsylvania, and was seen also in
Virginia, Delaware, New Jersey, New York, and Connecticut. Its course
was north, about thirty degrees east, and the projection of its path
on the earth's surface passed about four miles west of Lancaster,
Pennsylvania, and nearly through Mauch Chunk, in Carbon County. When
west of Philadelphia its angle of elevation, as seen from that city,
was forty-two degrees. Consequently its altitude, when near Lancaster,
was about fifty-nine miles. The projection of its visible path, on the
earth's surface, was at least two hundred and fifty miles in length.
Its height, when nearest Gettysburg, was about seventy miles, and it
disappeared at an elevation of about eighteen miles, near the south
corner of Wayne County, Pennsylvania. Its apparent diameter, as seen
from York and Lancaster, was about half that of the moon, and its
estimated heliocentric velocity was between twenty and twenty-five
miles.

The author was assured by persons in Harford County, Maryland, and also
in York, Pennsylvania, that shortly after the disappearance of the
meteor a distinct report, like that of a distant cannon, was heard.
As might be expected, their estimates of the interval which elapsed
were different; but Daniel M. Ettinger, Esq., of York, who was paying
particular attention, in expectation of a report, stated that it was
a little over six minutes. This would indicate a distance of about
seventy-five miles. The sound could not therefore have resulted from
an explosion at or near the termination of the meteor's observed path.
The inclination of the meteoric track to the surface of the earth
was such that the body could not have passed out of the atmosphere.
As no aerolites, however, were found beneath any part of its path,
perhaps the entire mass may have been dissipated before reaching the
earth.--_Silliman's Journal_ for May, 1866.

5. On the 14th of July, 1847, a remarkable fall of aerolites was
witnessed at Braunau, in Bohemia. Humboldt states that "the fallen
masses of stone were so hot, that, after six hours, they could not be
touched without causing a burn." An analysis of some of the fragments,
by Fischer and Duflos, gave the following result:

    Iron                                                91·862
    Nickel                                               5·517
    Cobalt                                               0·529
    Copper, manganese, arsenic, calcium, magnesium,
      silicium, carbon, chlorine and sulphur.            2·072
                                                       -------
                                                       100·000

6. On the 13th of July, 1848, a brilliant fire-ball was seen at
Stone-Easton, Somerset, England.

7. On the 13th of July, 1852, a large bolide was seen in London.

8. On the 14th of July, 1854, a fire-ball was seen at Senftenberg.

9. On the 13th of July, 1855, a meteor, three times as large as
Jupiter, was seen at Nottingham, England.

10. "One of the most celebrated falls that have occurred of late years
is that which happened on the 14th of July, 1860, between two and
half-past two in the afternoon, at Dhurmsala, in India. The aerolite in
question fell with a most fearful noise, and terrified the inhabitants
of the district not a little. Several fragments were picked up by
the natives, and carried religiously away, with the impression that
they had been thrown from the summit of the Himalayas by an invisible
Divinity. Lord Canning forwarded some of these stones to the British
Museum and to the Vienna Museum. Mr. J. R. Saunders also sent some
of the stones to Europe. It appears that, soon after their fall, the
stones were _intensely cold_.[15] They are ordinary earthy aerolites,
having a specific gravity of 3·151, containing fragments of iron and
iron pyrites; they have an uneven texture, and a pale-gray color."

11. At a quarter-past ten o'clock on the evening of July 13th, 1864,
a large fire-ball was seen in New England.[16] The hour of its
appearance, it will be observed, was nearly the same with that of the
bolide of July 13th, 1846; and it is also worthy of remark that their
_directions_ were nearly the same. The meteor of 1864 had a tail three
or four degrees in length, and the body, like that of 1846, exploded
with a loud report.

12. On the 8th of July, 1186, an aerolite fell at Mons, in Belgium
(Quetelet's _Physique du Globe_, p. 320). A forward motion of the node,
somewhat less than that observed in the rings of November and August,
would give a correspondence of dates between the falls of 1186, 1847,
and 1860.

With the exception of the last, which is doubtful, these phenomena all
occurred within a period of 67 years.


THE EPOCH OF NOVEMBER 29.

It has been stated that in different years meteoric stones have
fallen about the 29th of November. One of the most recent aerolites
which can be assigned to this epoch is that which fell on the 30th of
November, 1850, at Shalka, in Bengal. It may be mentioned, as at least
a coincidence, that the earth passes the approximate intersection of
her orbit with that of Biela's comet at the date of this epoch. Do
other bodies besides the two Biela comets move in the same ellipse? It
is worthy of remark that two star showers have been observed at this
date: one in China, A.D. 930, the other in Europe, 1850 (see Quetelet's
Catalogue). It is certainly important that the meteors of this epoch
should be carefully studied.



CHAPTER V.

 GEOGRAPHICAL DISTRIBUTION OF METEORIC STONES--DO AEROLITIC FALLS
 OCCUR MORE FREQUENTLY BY DAY THAN BY NIGHT?--DO METEORITES,
 BOLIDES, AND THE MATTER OF ORDINARY SHOOTING-STARS, COEXIST IN
 THE SAME RINGS?


Professor Charles Upham Shepard, of Amherst College, who has devoted
special attention to the study of meteoric stones, has designated two
districts of country, one in each continent, but both in the northern
hemisphere, in which more than nine-tenths of all known aerolites have
fallen. He remarks: "The fall of aerolites is confined principally
to two zones; the one belonging to America is between 33° and 44°
north latitude, and is about 25° in length. Its direction is more or
less from northeast to southwest, following the general line of the
Atlantic coast. Of all known occurrences of this phenomenon during the
last fifty years, 92·8 per cent. have taken place within these limits,
and mostly in the neighborhood of the sea. The zone of the Eastern
continent--with the exception that it extends ten degrees more to the
north--lies between the same degrees of latitude, and follows a similar
northeast direction, but is more than twice the length of the American
zone. Of all the observed falls of aerolites, 90·9 per cent. have taken
place within this area, and were also concentrated in that half of the
zone which extends along the Atlantic."

The facts as stated by Professor Shepard are, of course,
unquestionable. It seems, however, extremely improbable that the
districts specified should receive a much larger proportion of
aerolites than others of equal extent. How, then, are the facts to be
accounted for? We answer, the number of aerolites _seen_ to fall in a
country depends upon the number of its inhabitants. The ocean, deserts,
and uninhabited portions of the earth's surface afford no instances
of such phenomena, simply for the want of observers. In sparsely
settled countries the fall of aerolites would not unfrequently escape
observation; and as such bodies generally penetrate the earth to some
depth, the chances of discovery, when the fall is not observed, must be
exceedingly rare. Now the part of the American continent designated by
Professor Shepard, it will be noticed, is the oldest and most thickly
settled part of the United States; while that of the Eastern continent
stretches in like manner across the most densely populated countries
of Europe. This fact alone, in all probability, affords a sufficient
explanation of Prof. Shepard's statement.[17]

_Do aerolites fall more frequently by day than by night?_--Mr.
Alexander S. Herschel, of Collingwood, England, has with much care and
industry collected and collated the known facts in regard to bolides
and aerolites. One result of his investigations is that a much greater
number of meteoric stones are observed to fall by day than by night.
From this he infers that, for the most part, the orbits in which
they move are _interior_ to that of the earth. The fact, however, is
obviously susceptible of a very different explanation--an explanation
quite similar to that of the frequent falls in particular districts.
_At night the number of observers is incomparably less; and hence many
aerolites escape detection._ There would seem to be no cause, reason,
or antecedent probability of these falls being more frequent at one
hour than another in the whole twenty-four.

_The coexistence of meteorites, bolides, and the matter of
shooting-stars in the same rings?_--It has been stated on a previous
page that several aerolite epochs are coincident with those of
shooting-stars. Is the number of such cases sufficient to justify the
conclusion that the correspondence of dates is not accidental? We will
consider,


I. The Epoch of November 11th-14th.

1. 1548, November 6th. A very large detonating meteor was seen at
Mansfield, Thuringia, at two o'clock in the morning. The known rate of
movement of the node brings this meteor within the November epoch.

2. 1624, November 7th. A large fire-ball was seen at Tubingen. The
motion of the node brings this also within the epoch.

3. 1765, November 11th. A bright meteoric light was observed at
Frankfort.

4. 1791, November 11th. A large meteor was seen at Göttingen and
Lilienthal.

5. 1803, November 13th. A fire-ball, twenty-three miles high, was seen
at London and Edinburgh.

6. 1803, November 13th. A splendid meteor was seen at Dover and Harts.

7. 1808, November 11th. A fire-ball was seen in England.

8. 1818, November 13th. A fire-ball was seen at Gosport.

9. 1819, November 13th. A fire-ball was seen at St. Domingo.

10. 1820, November 12th. A large detonating meteor was seen at
Cholimschk, Russia.

11. 1822, November 12th. A fire-ball appeared at Potsdam.

12. 1828, November 12th. A meteor was seen in full sunshine at Sury,
France.

13. 1831, November 13th. A fire-ball was seen at Bruneck.

14. 1831, November 13th. A brilliant meteor was seen in the North of
Spain.

15. 1833, November 12th. A fire-ball was seen in Germany.

16. 1833, November 13th. A meteor, two-thirds the size of the moon, was
seen during the great meteoric shower in the United States.

17. 1834, November 13th. A large fire-ball was seen in North America.

18. 1835, November 13th. Several aerolites fell near Belmont,
Department de l'Ain, France.

19. 1836, November 11th. An aerolitic fall occurred at Macao, Brazil.

20. 1837, November 12th. A remarkable fire-ball was seen in England.

21. 1838, November 13th. A large fire-ball was seen at Cherbourg.

22. 1849, November 13th. An extraordinary meteor appeared in Italy.
"Seen in the southern sky. Varied in color; a bright cloud visible one
and a half hour after; according to some a detonation heard fifteen
minutes after bursting. Seen also like a stream of fire between Tunis
and Tripolis, where a shower of stones fell; some of them into the town
of Tripolis itself."

23. 1849, November 13th. A large meteor was seen at Mecklenburg and
Breslau.

24. 1856, November 12th. A meteoric stone fell at Trenzano, Italy.

25. 1866, November 14th. At Athens, Greece, a large number of
bolides was seen by Mr. J. F. Julius Schmidt, during the shower of
shooting-stars. One of these fire-balls was of the first class, and
left a train which was visible one hour to the naked eye.


II. The Epoch of August 7th-11th.

1. 1642, August 4th. A meteoric stone fell in Suffolk County, England.

2. 1650, August 6th. An aerolite fell in Holland. The observed motion
of the node brings both these stone-falls within the epoch.

3. 1765, August 9th. A large bolide was seen at Greenwich.

4. 1773, August 8th. A fire-ball was seen at Northallerton.

5. 1800, August 8th. A large meteor was seen in different parts of
North America.

6. 1802, August 10th. A fire-ball appeared at Quedlinburg.

7. 1807, August 9th. A bolide was seen at Nurenberg.

8. 1810, August 10th. A stone weighing seven and three-quarter pounds
fell at Tipperary, Ireland.

9. 1816, August 7th. In Hungary a large fire-ball was seen to burst,
with detonations.

10. 1817, August 7th. A brilliant fire-ball was seen at Augsburg.

11. 1818, August 10th. A meteoric stone, weighing seven pounds, fell at
Slobodka, Russia.

12. 1822, August 7th. A meteorite fell at Kadonah, Agra.

13. 1822, August 7th. A large meteor was seen in Moravia.

14. 1822, August 11th. "A large mass of fire fell down with a great
explosion" near Coblentz.

15. 1823, August 7th. Two meteoric stones fell in Nobleboro', Maine.

16. 1826, August 8th. A fire-ball was seen at Odensee.

17. 1826, August 11th. A bright meteor appeared at Halle.

18. 1833, August 10th. A fire-ball was seen at Worcestershire, England.

19. 1834, August 10th. A bolide appeared at Brussels.

20. 1838, August 9th. A fine meteor was seen in Germany.

21. 1839, August 7th. A splendid fire-ball was seen at sea.

22. 1840, August 7th. A bolide appeared at Naples.

23. 1841, August 10th. An aerolite fell at Iwan, Hungary.

24. 1842, August 9th. A greenish fire-ball was seen at Hamburg.

25. 1844, August 8th. A large meteor was seen in Brittany.

26. 1844, August 10th. A fire-ball was seen at Hamburg.

27. 1845, August 10th. A brilliant meteor was seen at London and Oxford.

28. 1847, August 9th. A large irregular meteor, "like a bright cloud of
smoke," was seen at Brussels.

29. 1850, August 10th. A meteor as large as the moon was seen in
Ireland.

30. 1850, August 10th. A very large bolide was observed in Paris.

31. 1850, August 11th. A fire-ball was seen in Paris.

32. 1853, August 7th. A bolide was observed at Glasgow.

33. 1853, August 7th. A meteor twice as large as Venus was seen at
Paris.

34. 1853, August 9th. A large meteor was seen to separate into two
parts.

35. 1855, August 10th. A bluish meteor, five times as large as Jupiter,
was seen at Nottingham.

36. 1857, August 11th. A bolide was seen in Paris.

37. 1859, August 7th. A detonating meteor appeared in Germany.

38. 1859, August 11th. A meteoric stone fell near Albany, New York.

39. 1859, August 11th. A fine meteor was seen at Athens.

40. 1862, August 8th. A meteoric stone-fall occurred at Pillistfer,
Russia.

41. 1863, August 11th. An aerolite fell at Shytal, India.


III. The Epoch of December 6th-13th.

The following falls of meteoric stones have occurred at this epoch:

1. 1795, December 13th. At Wold Cottage, England.

2. 1798, December 13th. At Benares, India.

3. 1803, December 13th. At Mässing, Bavaria.

4. 1813, December 13th. At Luotolaks, Finland.

5. 1858, December 9th. At Ausson, France.

6. 1863, December 7th. At Tirlemont, Belgium.

7. 1863, December 10th. At Inly, near Trebizond.[18]


IV. The Epoch of April 18th-26th.

For this epoch we have the following aerolites:

1. 1803, April 26th. At L'Aigle, France.

2. 1808, April 19th. At Casignano, Parma, Italy.

3. 1838, April 18th. At Abkurpore, India.

4. 1842, April 26th. At Milena, Croatia.


V. The Epoch of April 9th-12th.

1. 1805, April 10th. At Doroninsk, Russia.

2. 1812, April 10th. At Toulouse, France.

3. 1818, April 10th. At Zaborzika, Russia.

4. 1864, April 12th. At Nerft, Russia.

The foregoing lists, which might be extended, are sufficient to
establish the fact that meteoric stones are but the largest masses in
the nebulous rings from which showers of shooting-stars are derived; a
fact worthy of consideration whatever theory may be adopted in regard
to the origin of such annuli.



CHAPTER VI.

PHENOMENA SUPPOSED TO BE METEORIC--METEORIC DUST--DARK DAYS.


It is well known that great variety has been found in the composition
of aerolites. While some are extremely hard, others are of such a
nature as to be easily reducible to powder. It is not impossible
that when some of the latter class explode in the atmosphere they
are completely pulverized, so that, reaching the earth in extremely
minute particles, they are never discovered. It is very unlikely,
moreover, that of the millions of shooting-stars that daily penetrate
the atmosphere nothing whatever in the solid form should ever reach the
earth's surface. Indeed, the celebrated Reichenbach, who devoted great
attention to this subject, believed that he had actually discovered
such deposits of meteoric matter. Chladni and others have detailed
instances of the fall of _dust_, supposed to be meteoric, from the
upper regions of the atmosphere. The following may be regarded, with
more or less probability, as instances of such phenomena:

1. A.D. 475, November 5th or 6th. A shower of black dust fell in the
vicinity of Constantinople. Immediately before or about the time of
the fall, according to old accounts, "the heavens appeared to be on
fire," which seems to indicate a meteoric display of an extraordinary
character.

2. On the 3d of December, 1586, a considerable quantity of dark-colored
matter fell from the atmosphere, at Verde, in Hanover. The fall was
attended by intense light, as well as by a loud report resembling
thunder. The substance which fell was hot when it reached the earth,
as the planks on which a portion of it was found were slightly burnt,
or charred. The date of this occurrence, allowance being made for the
movement of the node, is included within the limits of the meteoric
epoch of December 6th-13th.

3. About a century later, viz., on the 31st of January, 1686, a very
extensive deposit of blackish matter, in appearance somewhat resembling
charred paper, took place in Norway and other countries in the north
of Europe. A portion of this substance, which had been carefully
preserved, was analyzed by Grotthus, and found to contain iron, silica,
and other elements frequently met with in aerolites.

4. On the 15th of November, 1755, red rain fell in Sweden and Russia,
and on the same day in Switzerland. It gave a reddish color to the
waters of Lake Constance, to which it also imparted an acid taste. The
rain which fell on this occasion deposited a sediment whose particles
were attracted by the magnet.

5. In 1791 a luminous meteor exploded over the Atlantic Ocean, and at
the same time a quantity of matter resembling sand descended to the
surface.

6. According to Chladni the explosion of a large bolide over Peru, on
the 27th of August, 1792, was followed by a shower of cindery matter,
the fall of which continued during three consecutive days.

7. On the 13th and 14th of March, 1813, a shower of red dust fell in
Calabria, Tuscany, and Friuli. The deposit was sufficient to impart
its color to the snow which was then upon the ground. That this dust
was meteoric can scarcely be doubted, since at the same time a shower
of aerolites fell at Cutro, in Calabria, attended by two loud reports
resembling thunder. The shower of dust continued several hours, and was
accompanied by a noise which was compared to the distant dashing of the
waves of the ocean.[19]

8. In November, 1819, black rain and snow fell in Canada.

9. On the 3d of May, 1831, red rain fell near Giessen. It deposited a
dark-colored sediment which Dr. Zimmermann found to contain silica,
oxide of iron, and various other substances observed in aerolites.

It is well known that quantities of sand are often conveyed, by the
trade-winds, from the continent of Africa and deposited in the ocean.
Such sand-showers have sometimes occurred several hundred miles from
the coast. Volcanic matter also has been occasionally carried a
considerable distance. The phenomena above described cannot, however,
be referred to such causes; and there can be little doubt that most, if
not all of them, were of meteoric origin.

There is, in all probability, a regular gradation from the smallest
visible shooting-stars to bolides and aerolites. No doubt a great
number of very small meteoric stones penetrate beneath the earth's
surface and escape observation. An interesting account of the
accidental discovery of such _celestial pebbles_ has recently been
given by Professor Haidinger, of Vienna. The meteor from which they
were derived _was but little larger than an ordinary shooting-star_.
Its track was visible, however, until it terminated at the earth's
surface. Professor Haidinger's account is as follows: On the 31st
of July, 1859, about half-past nine o'clock in the evening, three
inhabitants of the bourg of Montpreis, in Styria, saw a small luminous
globe, very similar to a shooting-star, and followed by a luminous
streak in the heavens, fall directly to the earth, which it attained
close to the château that exists in the locality. The fall was
accompanied by a whistling or hissing noise in the air, and terminated
by a _slight_ detonation. The three observers, rushing to the spot
where the meteor fell, immediately found a small cavity in the hard,
sandy soil, from which they extracted three small meteoric stones about
the size of nuts, and a quantity of black powder. For five to eight
seconds these stones continued in a _state of incandescence_, and it
was necessary to allow upwards of a quarter of an hour to elapse before
they could be touched without inflicting a burn. They appear to have
been ordinary meteoric stones, covered with the usual black rind. The
possessors would not give them up to be analyzed. The details of this
remarkable occurrence of the fall of an extremely small meteor, we owe
to Herr Deschann, Conservator of the Museum of Laibach, in Carniola,
and member of the Austrian Chamber of Deputies.

The following is perhaps the only instance on record in which a
shooting-star _lower than the clouds_ has been undoubtedly observed.
The date is one at which meteors are said to be more than usually
numerous; and the radiant point for the epoch has been recently
determined, by British observers, to be about _Gamma Cygni_. The
meteor was seen by Mr. David Trowbridge, of Hector, Schuyler County,
New York, who says: "On the evening of July 26th, 1866, about 8h.
15m. P.M., a very bright meteor flashed out in Cygnus, and moved from
east to west with great rapidity. Its path was about 30° after I saw
it. Height above the northern horizon about 50°. Duration of flight
from one-half to one second. It left a beautiful train. The head was
red and train blue. It was certainly _below_ the clouds. It passed
between me and some cirro-stratus clouds, so dense as to hide ordinary
stars completely. Several others that saw it said it was _below_ the
clouds."--_Silliman's Journal_ for Sept. 1866. It seems altogether
probable that when a meteor thus descends, before its explosion or
dissipation, into the lower atmospheric strata, at least portions of
its mass must reach the earth's surface.


METEORIC TRANSITS--DARK DAYS.

If shooting-stars and aerolites are derived from meteoric rings
revolving round the sun in orbits nearly intersecting that of the
earth, then (1) these masses must sometimes transit the solar disk; (2)
if any of the rings contain either individual masses of considerable
magnitude, or sufficiently dense swarms of meteoric asteroids, such
transits may sometimes be observed; (3) the passage of a dense meteoric
cluster over the solar disk must partially intercept the sun's light
and heat; and (4) should both nodes of the ring very nearly intersect
the earth's orbit, meteoric falls might occur when the earth is at
either; in which case the epochs would be separated by an interval
of about six months. Have any such phenomena as those indicated been
actually observed?

The passage of dark spots across the sun, having a much more rapid
motion than the solar maculæ, has been frequently noticed. The
following instances are well authenticated:

1779, June 17th. About mid-day the eminent French astronomer, Messier,
saw a great number of black points crossing the sun. Rapidly moving
spots were also seen by Pastorff on the following dates:

1822, October 23d,

1823, July 24th and 25th,

1836, October 18th,

and on several subsequent occasions the same astronomer witnessed
similar phenomena. Another transit of this kind has been seen quite
recently. On the 8th of May, 1865, a small black spot was seen by
Coumbary to cross the solar disk. It seems difficult to account for
these appearances (so frequently seen by experienced observers) unless
we regard them as meteoric masses.


PARTIAL INTERCEPTION OF THE SUN'S LIGHT AND HEAT.

Numerous instances are on record of partial obscurations of the sun
which could not be accounted for by any known cause. Cases of such
phenomena took place, according to Humboldt, in the years 1090, 1203,
and 1547. Another so-called _dark day_ occurred on the 12th of May,
1706, and several more (some of still later date) might be specified.
Chladni and other physicists have regarded the transit of meteoric
masses as the most probable cause of these obscurations. It is proper
to remark, however, that the eminent French astronomer, Faye, who
has given the subject much attention, finds little or no evidence in
support of this conjecture.

An examination of meteorological records is said to have established
two epochs of abnormal cold, viz., about the 12th of February and the
12th of May. The former was pointed out by Brandes about the beginning
of the present century; the latter by Mädler, in 1834. The May epoch
occurs when the earth is in conjunction with one of the nodes of the
November meteoric ring; and that of February has a similar relation
to the August meteors. M. Erman, a distinguished German scientist,
soon after the discovery of the August and November meteoric epochs,
suggested that those depressions of temperature might be explained
by the intervention of the meteoric zones between the earth and the
sun. The period, however, of the November meteors being still somewhat
doubtful, their position with respect to the earth about the 12th of
May is also uncertain. But however this may be, the following dates
of aerolitic falls seem to indicate May 8th-14th, or especially May
12th-13th, as a meteoric epoch:

(_a_) May 8th, 1829, Forsyth, Georgia, U. S. A.

(_b_) May 8th, 1846, Macerata, Italy.

(_c_) May 9th, 1827, Nashville, Tennessee, U. S. A.

(_d_) May 12th, 1861, Goruckpore, India.

(_e_) May 13th, 1831, Vouillé, France.

(_f_) May 13th, 1855, Oesel, Baltic Sea.

(_g_) May 13th, 1855, Bremevörde, Hanover.

(_h_) May 14th, 1861, near Villanova, in Catalonia, Spain.

(_i_) May 14th, 1864, Orgueil, France.

All the foregoing, except that of May 14th, 1861, may be found in
Shepard's list, _Silliman's Journal_ for January, 1867.

It has been shown in a former chapter that more than seven millions
of shooting-stars of sufficient magnitude to be seen by the naked eye
daily enter the earth's atmosphere. As the small ones are the most
numerous, it is not improbable that an indefinitely greater number of
meteoric particles, too minute to be visible, are being constantly, in
this manner, arrested in their orbital motion. Now, it would certainly
be a very unwarranted conclusion that these atmospheric increments are
all of a permanently gaseous form. In view of this strong probability
that meteoric dust is daily reaching the earth's surface, Baron von
Reichenbach, of Vienna, conceived the idea of attempting its discovery.
Ascending to the tops of some of the German mountains, he carefully
collected small quantities of the soil from positions in which it had
not been disturbed by man. This matter, on being analyzed, was found
to contain small portions of nickel and cobalt--elements rarely found
in the mineral masses scattered over the earth's surface, but very
frequently met with in aerolites. In short, Reichenbach believed, and
certainly not without some probability, that he had detected minute
portions of meteoric matter.



CHAPTER VII.

 FURTHER RESEARCHES OF REICHENBACH--THEORY OF METEORS--STABILITY OF
 THE SOLAR SYSTEM--DOCTRINE OF A RESISTING MEDIUM.


The able and original researches of the celebrated Reichenbach, who has
made meteoric phenomena the subject of long-continued and enthusiastic
investigation, have attracted the general attention of scientific men.
It is proposed to present, in the following chapter, a brief _resumé_
of his views and conclusions.

1. _The Constitution of Comets._--It is a remarkable fact that cometary
matter has no refractive power, as is manifest from the observations of
stars seen through their substance.[20] These bodies, therefore, are
not gaseous; and the most probable theory in regard to their nature is
that they consist of an infinite number of discrete, solid molecules,
at great distances from each other, with very little attraction among
themselves, or toward the nucleus, and having, therefore, great
mobility. Now Baron Reichenbach, having carefully examined a great
number of meteoric stones, has found them for the most part composed
of extremely minute globules, apparently cemented together. He hence
infers that they have been comets--perhaps very small ones--whose
component molecules have by degrees collected into single masses.

2. _The Number of Aerolites._--The average number of aerolitic falls
in a year was estimated by Schreibers, as previously stated, at 700.
Reichenbach, however, after a thorough discussion of the data at
hand, makes the number much larger. He regards the probable annual
average, for the entire surface of the earth, as not less than 4500.
This would give about twelve daily falls. They are of every variety
as to magnitude, from a weight of less than a single ounce to over
30,000 pounds. The Baron even suspects the meteoric origin of large
masses of dolerite which all former geologists had considered native
to our planet. In view of the fact that from the largest members of
our planetary system down to the particles of meteoric dust there is
an approximately regular gradation, and that the larger, at least
in some instances, appear to have been formed by the aggregation of
the smaller, he asks may not the earth itself have been formed by an
agglomeration of meteorites? The learned author, from the general scope
of his speculations, would thus seem to have adopted a form of the
nebular hypothesis somewhat different from that proposed by Laplace.

3. _Composition and mean Density of Aerolites._--A large proportion of
meteoric stones are similar in structure to the volcanic or plutonic
rocks of the earth; and _all_ consist of elements identical with
those in our planet's crust. Their mean density, moreover, is very
nearly the same with that of the earth. These facts are regarded by
Reichenbach as indicating that those meteoric masses which are daily
becoming incorporated with our planet, have had a common origin with
the earth itself. Baron Reichenbach's views, as presented by himself,
will be found at length in _Poggendorf's Annalen_ for December, 1858.

_Stability of the Solar System._--The well-known demonstrations of
the stability of the solar system, given by Lagrange and Laplace,
are not to be accepted in an unlimited sense. They make no provision
against the destructive agency of a resisting medium, or the entrance
of matter into the solar domain from the interstellar spaces. In
short, the conservative influence ascribed to these celebrated
theorems extends only to the major planets; and even in their case it
is to be understood as applying only to their mutual perturbations.
The phenomena of shooting-stars and aerolites have demonstrated the
existence of considerable quantities of matter moving in _unstable_
orbits. The amount of such matter within the solar system cannot now be
determined; but the term probably includes the zodiacal light, many,
if not all, of the meteoric rings, and a large number of comets. These
unstable parts of the system are being gradually incorporated with the
sun, the earth, and doubtless also with the other large planets. It is
highly probable that at former epochs the quantity of such matter was
much greater than at present, and that, unless new supplies be received
_ab extra_, it must, by slow degrees, disappear from the system.

The fact, now well established, of the extensive diffusion of meteoric
matter through the interplanetary spaces has an obvious bearing on
Encke's theory of a resisting medium. If we grant the existence of such
an ether, it would seem unphilosophical to ascribe to it one of the
properties of a material fluid--the power of resisting the motion of
all bodies moving through it--and to deny it such properties in other
respects. Its condensation, therefore, about the sun and other large
bodies must be a necessary consequence. This condensation existed in
the primitive solar spheroid, before the formation of the planets:
the rotation of the spheroid would be communicated to the coexisting
ether; and hence, _during the entire history of the planetary system,
the ether has revolved around the sun in the same direction with the
planets_. This condensed ether, it is also obvious, must participate in
the progressive motion of the solar system.

But again; even if we reject the doctrine of the development of the
planetary bodies from a rotating nebula, we must still regard the
density of the ether as increasing to the center of the system. The
sun's rotation, therefore, would communicate motion to the first and
denser portions; this motion would be transmitted outward through
successive strata, with a constantly diminishing angular velocity.
The motion of the planets themselves through the medium in nearly
circular orbits would concur in imparting to it a revolution in the
same direction. Whether, therefore, we receive or reject the nebular
hypothesis, the resistance of the ethereal medium to bodies moving
in orbits of small eccentricity and in the direction of the sun's
rotation, becomes an infinitesimal quantity.

The hypothesis of Encke, it is well known, was based solely on the
observed acceleration of the comet which bears his name. More recently,
however, a still greater acceleration has been found in the case of
Faye's comet. Now as the meteoric matter of the solar system is a
_known_ cause for such phenomena, sufficient, in all probability, both
in mode and measure, the doctrine of a resisting ethereal medium would
seem to be a wholly unnecessary assumption.



CHAPTER VIII.

 DOES THE NUMBER OF AEROLITIC FALLS VARY WITH THE EARTH'S DISTANCE
 FROM THE SUN?--RELATIVE NUMBERS OBSERVED IN THE FORENOON AND
 AFTERNOON--EXTENT OF THE ATMOSPHERE AS INDICATED BY METEORS.


An analysis of any extensive table of meteorites and fire-balls proves
that a greater number of aerolitic falls have been observed during the
months of June and July, when the earth is near its aphelion, than in
December and January, when near its perihelion. It is found, however,
that the reverse is true in regard to bolides, or fire-balls. Now the
theory has been held by more than one physicist, that aerolites are
the outriders of the asteroid ring between Mars and Jupiter; their
orbits having become so eccentric that in perihelion they approach
very near that of the earth. If this theory be the true one, the earth
would probably encounter the greatest number of those meteor-asteroids
when near its aphelion. The hypothesis therefore, it has been claimed,
appears to be supported by well-known facts. The variation, however,
in the observed number of aerolites may be readily accounted for
independently of any theory as to their origin. The fall of meteoric
stones would evidently be more likely to escape observation by night
than by day, by reason of the relatively small number of observers. But
the days are shortest when the earth is in perihelion, and longest when
in aphelion; the ratio of their lengths being nearly equal to that of
the corresponding numbers of aerolitic falls.

On the other hand, it is obvious that fire-balls, unless of very
extraordinary magnitude, would not be visible during the day. The
_observed_ number will therefore be greatest when the nights are
longest; that is, when the earth is near its perihelion. This, it will
be found, is precisely in accordance with observation.

It has been found, moreover, that a greater number of meteoric stones
fall during the first half of the day, that is, from midnight to noon,
than in the latter half, from noon to midnight. This would seem to
indicate that a large proportion of the aerolites encountered by the
earth have direct motion.

_Height of the Atmosphere._--The weight of a given volume of mercury is
10,517 times that of an equal volume of air at the earth's surface; and
since the mean height of the mercurial column in the barometer is about
thirty inches, if the atmosphere were of uniform density its altitude
would be about 26,300 feet, or nearly five miles. The density rapidly
diminishes, however, as we ascend above the earth's surface. Calling
it unity at the sea level, the rate of variation is approximately
expressed as follows:

    Altitude in Miles.        Density.

      0                          1
      7                         1/4
     14                        1/16
     21                        1/64
     28                        1/256
     35                       1/1024
     70                      1/1000000
    105                    1/1000000000
    140                   1/1000000000000
    etc.                        etc.

From this table it will be seen that at the height of 35 miles the air
is one thousand times rarer than at the surface of the earth; and that,
supposing the same rate of decrease to continue, at the height of 140
miles the rarity would be one trillion times greater. The atmosphere,
however, is not unlimited. When it becomes so rare that the force of
repulsion between its particles is counterbalanced by the earth's
attraction, no further expansion is possible. To determine the altitude
of its superior surface is a problem at once difficult and interesting.
Not many years since about 45 or 50 miles were generally regarded as a
probable limit. Considerable light, however, has been thrown upon the
question by recent observations in meteoric astronomy. Several hundred
detonating meteors have been observed, and their average height at the
instant of their first appearance has been found to exceed 90 miles.
The great meteor of February 3d, 1856, seen at Brussels, Geneva, Paris,
and elsewhere, was 150 miles high when first seen, and a few apparently
well-authenticated instances are known of a still greater elevation. We
conclude, therefore, from the evidence afforded by meteoric phenomena,
that the height of the atmosphere is certainly not _less_ than 200
miles.

It might be supposed, however, that the resistance of the air at
such altitudes would not develop a sufficient amount of heat to
give meteorites their brilliant appearance. This question has been
discussed by Joule, Thomson, Haidinger, and Reichenbach, and may now
be regarded as definitively settled. When the velocity of a meteorite
is known the quantity of heat produced by its motion through air of
a given density is readily determined. The temperature acquired is
the equivalent of the force with which the atmospheric molecules are
met by the moving body. This is about one degree (Fahrenheit) for a
velocity of 100 feet per second, and it varies directly as the square
of the velocity. A velocity, therefore, of 30 miles in a second
would produce a temperature of 2,500,000°. The weight of 5280 cubic
feet of air at the earth's surface is about 2,830,000 grains. This,
consequently, is the weight of a column 1 mile in length, and whose
base or cross section is one square foot. The weight of a column of the
same dimensions at a height of 140 miles would be about 1/350000th of a
grain. Hence the heat acquired by a meteoric mass whose cross section
is one square foot, in moving 1 mile would be one grain raised 7-1/7
degrees, or one-fifth of a grain 2500° in 70 miles. This temperature
would undoubtedly be sufficient to render meteoric bodies brilliantly
luminous.

But there have been indications of an atmosphere at an elevation of
more than 500 miles. A discussion of the best observations of the
great aurora seen throughout the United States on the 28th of August,
1859, gave 534 miles as the height of the upper limit above the
earth's surface. The aurora of September 2d, of the same year, had an
elevation but little inferior, viz., 495 miles. Now, according to the
observed rate of variation of density, at the height of 525 miles, the
atmosphere would be so rare that a sphere of it filling the orbit of
Neptune would contain less matter than 1/30th of a cubic inch of air at
the earth's surface. In other words, it would weigh less than 1/90th
of a grain. We are thus forced to the conclusion either that the law
of variation is not the same at great heights as near the surface; or,
that beyond the limits of the atmosphere of air, there is another of
electricity, or of some other fluid.



CHAPTER IX.

THE METEORIC THEORY OF SOLAR HEAT.


Of the various theories proposed by astronomers to account for the
origin of the sun's light and heat, only two have at present any
considerable number of advocates. These are--

1. _The Chemical Theory_; according to which the light and heat of the
sun are produced by the chemical combination of its elements; in other
words, by an intense combustion.

2. _The Meteoric Theory_, which ascribes the heat of our central
luminary to the fall of meteors upon its surface. The former is
advocated with great ingenuity by Professor Ennis in a recent work on
"_The Origin of the Stars, and the Causes of their Motions and their
Light_." It has, on the other hand, been ably opposed by Dr. Mayer,
Professor William Thomson, and other eminent physicists. A brief
examination of its claims may not be destitute of interest.

If the sun's heat is produced by chemical action, whence comes the
necessary supply of fuel to support the combustion? The quantity of
solar heat radiated into space has been determined with at least an
approximation to mathematical precision. We know also the amount
produced by the combustion of a given quantity of coal. Now it has been
found by calculation that if the sun were a solid globe of coal, and a
sufficient supply of oxygen were furnished to support its combustion,
the amount of heat resulting from its consumption would be less than
that actually emitted during the last 6000 years. In short, _no known_
elements would meet the demands of the case. But it is highly probable
that the different bodies of the solar system are composed of the same
elements. This view is sustained by the well-known fact that meteoric
stones, which have reached us from different and distant regions of
space, have brought us no new elementary substances. The _chemical_
theory of solar heat seems thus encumbered with difficulties well-nigh
insuperable.

Professor Ennis' mode of obviating this objection, though highly
ingenious, is by no means conclusive. The latest analyses of the solar
spectrum indicate, he affirms, the presence of numerous elements
besides those with which we are acquainted. Some of these may yield
by their combustion a much greater amount of heat than the same
quantity of any known elements in the earth's crust. "Every star," he
remarks, "as far as yet known, has a different set of fixed lines,
although there are certain resemblances between them. They lead to
the conclusion that each star has, in part at least, its peculiar
modifications of matter, called simple elements; but the number of
stars is infinite, and therefore the number of elements must be
infinite."[21] He argues, moreover, that in a globe so vast as the
sun there may be forces in operation with whose nature we are wholly
unacquainted. This leaving of the _known_ elements as well as the
_known_ laws of nature for _unknown possibilities_ will hardly be
satisfactory to unbiased minds.

Again: that the different bodies of the universe are composed of
different elements is inferred by our author from the following among
other considerations: "In our solar system Mercury is sixty or eighty
times more dense than one of the satellites of Jupiter, and probably in
a much greater proportion denser than the satellites of Saturn. This
indicates a wide difference between the nature of their elements." This
statement is again repeated in a subsequent page.[22] "The densities of
the planets and their satellites prove that they are composed of very
different elements. Mercury is more than sixty times, and our earth
about fifty times, more dense than the inner moon of Jupiter. Saturn is
only about one-ninth as dense as the earth; it would float buoyantly on
water. There is a high probability that the satellites of Saturn and
Uranus are far lighter than those of Jupiter. Between the two extremes
of the attendants of the sun, there is probably a greater difference
in density than one hundred to one; and from one extreme to the other
there are regular gradations of small amount.

"The difference in constitution between the earth and the moon is
seen in their densities: that of the moon being about half that of
the earth. The nitrogen of our globe is found only in the atmosphere,
and such substances as derive it from the atmosphere. The moon has
no appreciable atmosphere, and therefore, in a high probability, no
nitrogen."

The statements here quoted were designed to show that the physical
constitution of the sun and planets is widely different from that of
the earth, and that the combustion of _some_ of the elements in this
indefinite variety may account for the origin of solar heat. Let us
examine the facts.

According to Laplace the mass of Jupiter's first satellite is
0·000017328, that of Jupiter being 1. The diameter is 2436 miles. Hence
the corresponding density is a little more than _one-fifth_ of the mean
density of the earth. In other words, it is somewhat greater than the
density of water, and very nearly equal to that of Jupiter himself.
Professor Ennis' value is therefore erroneous.[23] In regard to the
densities of the Saturnian and Uranian satellites nothing is known,
and conjecture is useless. In short, Saturn has the least mean density
of all the planets, primary or secondary, so far as known. This may be
owing to the great extent of his atmospheric envelope. The density of
the moon is but three-fifths that of the earth: it is to be borne in
mind, however, that the _mass_ and _pressure_ are also much less.

With respect to meteorites the same author remarks that "like the
moon, they are probably satellites of the earth; but being very small,
they are liable to extraordinary perturbations, and hence strike the
earth in many directions." Here, again, his _facts_ are at fault; for
(1) the observed velocities of these bodies are inconsistent with the
supposition of their being satellites of the earth; and (2) the amount
of perturbation of such bodies does not vary with their masses: a
_small_ meteorite would fall toward the earth or any other planet with
no greater velocity than a _large_ one.


THE METEORIC THEORY.

It has been shown in a previous chapter that immense numbers of
meteoric asteroids are constantly traversing the planetary spaces--that
many millions, in fact, daily enter the earth's atmosphere. Reasons
are not wanting for supposing the numbers of these bodies to increase
with great rapidity as we approach the center of the system. Moreover,
on account of the greater force of gravity at the sun's surface the
heat produced by their fall must be much greater than at the surface
of the earth. It has been calculated that if one of these asteroids
be arrested in perihelion by the solar atmosphere, the quantity of
heat thus developed will be 9000 times greater than that produced by
the combustion of an equal mass of coal. There can, therefore, be no
reasonable doubt that a _portion_ of the sun's heat is produced by
the impact of meteoric matter. In considering the probability that it
is _chiefly_ so generated, the following questions naturally present
themselves:

1. _What amount of matter precipitated upon the sun would develop
the quantity of heat actually emitted?_--This question has been
satisfactorily discussed by eminent physicists, and it will be
sufficient for our purpose to give the result. According to Professor
William Thomson, of Glasgow, the present rate of emission would be kept
up by a meteoric deposit which would form an annual stratum 60 feet in
thickness over the sun's surface.

2. _Could such an increase of the sun's magnitude be detected by
micrometrical measurement?_--This inquiry is readily answered in the
negative. The apparent diameter would be augmented only one second in
17,600 years.

3. _Is there any known or visible source from which this amount
of meteoric matter may be supplied?_--Thomson, Mayer, and other
distinguished writers regard the zodiacal light as the source of
such meteorites. The inner portions of this immense "tornado" must
be resisted in their motions by the solar atmosphere, and hence
precipitated upon the sun's surface.

4. _Would this increase of the sun's mass derange the motions of the
solar system?_--To this question Prof. Ennis gives an affirmative
answer; his first objection to the theory under consideration being
stated as follows: "The constant accumulation of such materials,
during hundreds of millions of years, would increase the body of the
sun and its consequent gravity so greatly as to derange the entire
solar system, by destroying the balance between the centripetal and
centrifugal forces now acting on the planets."[24] This, it must be
confessed, would be a valid objection, if the meteoric matter were
supposed to be derived from the extra-planetary spaces. As their
source, however,--the zodiacal light--is interior to the earth's orbit,
it can have no application to any planet exterior to Venus. Most
probably the greater portion of the meteoric mass is even within the
orbit of Mercury, so that the effect of its convergence could scarcely
be noticed even in the motion of the interior planets. In pre-historic
time the zodiacal light may have extended far beyond the earth's orbit.
If so, its convergence to its present dimensions was undoubtedly
attended by an acceleration of the earth's mean motion. We can of
course have no evidence that such a shortening of the year has never
occurred.

The second objection urged against the meteoric theory by the author
of "The Origin of the Stars" is thus expressed: "As we must believe
that all stars were lighted up by the same means, so we must believe,
according to this theory, that the present interior heat of the earth
and its former melted condition in both exterior and interior, was
caused by the fall of meteorites. But if so, they must have gradually
ceased to fall, as space became cleared of their presence, and we would
now find a thick covering of meteorites on the earth's cooled surface.
Instead of this, we find them very rarely, and in accordance with their
present very rare falls."

To this it may be replied that the primitive igneous fluidity of the
earth and planets was a necessary consequence of their condensation--a
fact which has no inconsistency with the theory in question.

A different _mechanical_ theory of the origin of solar heat is
advocated by Professor Helmholtz in his interesting work _On the
Interaction of Natural Forces_. In regard to the sun he says: "If we
adopt the very probable view, that the remarkably small density of so
large a body is caused by its high temperature, and may become greater
in time, it may be calculated that if the diameter of the sun were
diminished only the ten-thousandth part of its present length, by this
act a sufficient quantity of heat would be generated to cover the
total emission for 2100 years. Such a small change besides it would be
difficult to detect by the finest astronomical observations."[25] The
same view is adopted by Dr. Joel E. Hendricks, of Des Moines, Iowa.[26]



CHAPTER X.

WILL THE METEORIC THEORY ACCOUNT FOR THE PHENOMENA OF VARIABLE AND
TEMPORARY STARS?


Having shown that meteor-asteroids are diffused in vast quantities
throughout the universe; that according to eminent physicists the
solar heat is produced by the precipitation of such matter on the
sun's surface; and that Leverrier has found it necessary to introduce
the disturbing effect of meteoric rings in order fully to account
for the motion of Mercury's perihelion; we now propose extending the
meteoric theory to a number of phenomena that have hitherto received no
satisfactory explanation.


VARIABLE AND TEMPORARY STARS.

No theory as to the origin of the sun's light and heat would seem to
be admissible unless applicable also to the sidereal systems. Will the
meteoric theory explain the phenomena of variable and temporary stars?

"It has been remarked respecting variable stars, that in passing
through their successive phases, they are subject to sensible
irregularities, which have not hitherto been reduced to fixed laws. In
general they do not always attain the same maximum brightness, their
fluctuations being in some cases very considerable. Thus, according
to Argelander, the variable star in _Corona Borealis_, which Pigott
discovered in 1795, exhibits on some occasions such feeble changes of
brightness, that it is almost impossible to distinguish the maxima
from the minima by the naked eye; but after it has completed several
of its cycles in this manner, its fluctuations all at once become
so considerable, that in some instances it totally disappears. It
has been found, moreover, that the light of variable stars does not
increase and diminish symmetrically on each side of the maximum, nor
are the successive intervals between the maxima exactly equal to each
other."--_Grant's History of Physical Astronomy_, p. 541.

Of the numerous hypotheses hitherto proposed to account for these
phenomena we believe none can be found to include and harmonize all
the facts of observation. The theories of Herschel and Maupertius fail
to explain the irregularity in some of the periods; while those of
Newton and Dunn afford no explanation of the periodicity itself.[27]
But let us suppose that among the fixed stars some have atmospheres
of great extent, as was probably the case with the sun at a remote
epoch in its history. Let us also suppose the existence of nebulous
rings, like those of our own system, moving in orbits so elliptical
that in their perihelia they pass through the atmospheric envelopes
of the central stars. Such meteoric rings of varying density, like
those revolving about the sun, would evidently produce the phenomena
of variable stars. The resisting medium through which they pass in
perihelion must gradually contract their orbits, or, in other words,
diminish the intervals between consecutive maxima. Such a shortening of
the period is now well established in the case of _Algol_. Again, if a
ring be influenced by perturbation the period will be variable, like
that of _Mira Ceti_. A change, moreover, in the perihelion distance
will account for the occasional increase or diminution of the apparent
magnitude at the different maxima of the same star. But how are we
to account for the variations of brightness observed in a number of
stars where no order or periodicity in the variation has as yet been
discovered? It is easy to perceive that either a single nebulous ring
with more than one _hiatus_, or several rings about the same star, may
produce phenomena of the character described. Finally, if the matter of
an elliptic ring should accumulate in a single mass, so as to occupy a
comparatively small arc, its passage through perihelion might produce
the phenomenon of a so-called temporary star.

Recent researches relating to nebulæ seem in some measure confirmatory
of the view here presented. These observations have shown (1) a change
of position in some of these objects, rendering it probable that in
certain cases they are not more distant than fixed stars visible to
the naked eye; and (2) a variation in the brilliancy of many small
stars situated in the great nebula of Orion, and also the existence
of numerous masses of nebulous matter in the form of tufts apparently
attached to stars,--facts regarded as indicative of a physical
connection between the stars and nebulæ.[28]



CHAPTER XI.

THE LUNAR AND SOLAR THEORIES OF THE ORIGIN OF AEROLITES.


Besides the _cosmical_ theory of aerolites which has been adopted in
this work, and which is now accepted by a great majority of scientific
men, at least four others have been proposed: (1) the _atmospheric_,
according to which they are formed, like hail, in the earth's
atmosphere; (2) the _volcanic_, which regards them as matter ejected
with great force from terrestrial volcanoes; (3) the _lunar_, which
supposes them to have been thrown from craters in the moon; and (4)
the _solar_ hypothesis, according to which they are projected by some
tremendous explosive force from the great central orb of our system.
The first and second have been universally abandoned as untenable. The
third and fourth, however, are entitled to consideration.


THE LUNAR THEORY.

The theory which regards meteoric stones as products of eruption in
lunar volcanoes was received with favor by the celebrated Laplace: "As
the gravity at the surface of the moon," he remarks, "is much less
than at the surface of the earth, and as this body has no atmosphere
which can oppose a sensible resistance to the motion of projectiles,
we may conceive that a body projected with a great force, by the
explosion of a lunar volcano, may attain and pass the limit, where
the attraction of the earth commences to predominate over that of the
moon. For this purpose it is sufficient that its initial velocity in
the direction of the vertical may be 2500 meters in a second; then in
place of falling back on the moon, it becomes a satellite of the earth,
and describes about it an orbit more or less elongated. The direction
of its primitive impulsion may be such as to make it move directly
toward the atmosphere of the earth; or it may not attain it, till after
several and even a great number of revolutions; for it is evident that
the action of the sun, which changes in a sensible manner the distances
of the moon from the earth, ought to produce in the radius vector of a
satellite which moves in a very eccentric orbit, much more considerable
variations, and thus at length so diminish the perigean distance of the
satellite, as to make it penetrate our atmosphere. This body traversing
it with a very great velocity, and experiencing a very sensible
resistance, might at length precipitate itself on the earth; the
friction of the air against its surface would be sufficient to inflame
it, and make it detonate, provided that it contained ingredients proper
to produce these effects, and then it would present to us all those
phenomena which meteoric stones exhibit. If it was satisfactorily
proved that they are not produced by volcanoes, or generated in our
atmosphere, and that their cause must be sought beyond it, in the
regions of the heavens, the preceding hypothesis, which likewise
explains the identity of composition observed in meteoric stones, by an
identity of origin, will not be devoid of probability."--_Système du
Monde_, t. ii. cap. v.

Knowing the masses and volumes of the earth and moon, it is easy to
estimate the force of gravity at their surfaces, the distance from each
to the point of equal attraction, and the force with which a projectile
must be thrown from the lunar surface to pass within the sphere of the
earth's influence. It has been calculated that an initial velocity
of about a mile and a half in a second would be sufficient for this
purpose--a force not greater than that known to have been exerted by
terrestrial volcanoes. The _possibility_, therefore, that volcanic
matter from our satellite may reach the earth's surface seems fairly
admissible.

Since the time of Laplace, several distinguished European astronomers
have regarded the lunar hypothesis as more or less probable. It was
advocated as recently as 1851 by the late Prof. J. P. Nichol, of
Glasgow. This popular and interesting writer, after describing Tycho, a
large and well-known lunar crater, from which luminous rays or stripes
radiate over a considerable part of the moon's surface, expresses the
opinion that that immense cavity was formed by a single tremendous
explosion. "Reflecting," he remarks, "on the probable suddenness and
magnitude of that force, or rather of that _explosive_ energy one of
whose acts we have traced, as well as on the immense mass of matter
which seems to have been thus violently dispersed, is not the inquiry
a natural one, _where is that matter now_? It is a mass indeed which
cannot well have wholly disappeared. It filled a cavern 55 miles in
breadth, and 17,000 feet deep--a cavern into which even now one might
cast Chimborazo and Mont Blanc, and room be left for Teneriffe behind!
Like rocks flung aloft by our volcanoes, did this immense mass fall
back in fragments to the surface of the moon, or was the expulsive
force strong enough to give it an outward velocity sufficient to resist
the attractive power of its parent globe? The moon, be it recollected,
is very small in _mass_ compared with the earth, and her attractive
energy greatly inferior accordingly. Laplace has even calculated that
the force urging a cannon-ball, increased to a degree quite within
the limits of what is conceivable, could effect a final separation
between our satellite and any of its component parts. It is _possible_
then, and, although not demonstrable, very far from a chimera, that
the disrupted and expelled masses were, in the case of which we are
speaking, driven conclusively into space; but if so, where are they
now? where their new residence, and what their functions? In the
emergency to which I refer, such fragments would necessarily wander
among the interplanetary spaces in most irregular orbits, and chiefly
in the neighborhood of the moon and the earth. Now, while the planetary
orbits are so nicely adjusted that neither confusion nor interference
can ever occur, it is not at all likely that the same order could be
established here; nay, it is next to certain, that in the course of its
orbital revolution our globe would ever and anon come in contact with
these lunar fragments; in other words, STONES _would fall occasionally
to its surface, and apparently from its atmosphere_."--_Planetary
System_, pp. 301, 302.

We have preferred to give the views of these eminent scientists in
their own language. Olbers, Biot, and Poisson, who adopted the same
theory, estimated the _initial_ velocity which would be necessary in
order that lunar fragments might pass the point of equal attraction,
and also the _final_, or acquired velocity on reaching the earth's
surface. The several determinations of the former were as follows:

    According to Olbers     1·570 miles a second.
         "       Biot       1·569   "       "
         "       Laplace    1·483   "       "
         "       Poisson    1·437   "       "

The mean being almost exactly a mile and a half. The velocity on
reaching our planet, according to Olbers, would be about six and a half
miles. At the date of these calculations, however, the true velocity
of aerolites had not been in any case satisfactorily determined. Since
that time it has been found in numerous instances to exceed _twenty
miles a second_--a velocity greater than that of the earth's orbital
motion. This fact of itself would seem fatal to the theory of a lunar
origin.

At the meeting of the American Association for the Advancement of
Science, in 1859, Dr. B. A. Gould read a paper on the supposed lunar
origin of aerolites, in which the hypothesis was subjected to the test
of a rigid mathematical analysis. We will not attempt even an abstract
of this interesting memoir. It amounts, however, to a virtual disproof
of the lunar hypothesis.


THE SOLAR THEORY.

The theory which ascribes a solar origin to meteorites is not of recent
date, having been held by Diogenes Laertius and other ancient Greeks.
Among the moderns its advocates have been much less numerous than those
of the lunar hypothesis. The late Professor Charles W. Hackley, of New
York, regarded shooting-stars, aerolites, and even comets, as matter
projected with enormous force from the solar surface. The corona seen
during total eclipses of the sun he supposed to be the emanations of
this matter through the intervals of the luculi.--(See the Proceedings
of the American Association for the Advancement of Science, Fourteenth
Meeting, 1860.) An ingenious theory, differing in its details from that
of Professor Hackley, though somewhat similar in its general features,
has lately been advocated by Alexander Wilcocks, M.D., of Philadelphia,
in a memoir read before the American Philosophical Society, May 20th,
1864, and published in their Proceedings. In regard to this hypothesis
it seems sufficient to remark that it fails to give a satisfactory
account of the annual periodicity of meteoric phenomena.



CHAPTER XII.

THE RINGS OF SATURN.


Until about the middle of the present century the rings of Saturn were
universally regarded as solid and continuous. The labors, however, of
Professors Bond and Pierce, of Cambridge, Massachusetts, as well as the
more recent investigations of Prof. Maxwell, of England, have shown
this hypothesis to be wholly untenable. The most probable opinion,
based on the researches of these astronomers, is, that they consist of
streams or clouds of meteoric asteroids. The zodiacal light and the
zone of small planets between Mars and Jupiter appear to constitute
analogous _primary_ rings. In the latter, however, a large proportion
of the primitive matter seems to have collected in distinct, segregated
masses. These meteoric zones have probably presented--what are not
elsewhere found in the solar system--cases of commensurability in the
planetary periods. The interior satellites of Saturn are so near the
ring as doubtless to exert great perturbative influence. Unfortunately,
the elements of the Saturnian system as determined by different
astronomers are somewhat discordant. This, however, is by no means
surprising when we consider the great distance of the planet and the
small magnitude of some of the satellites. For convenience of reference
the mean apparent distances of the satellites, together with their
periodic times, are given in the following table. The former are taken
from Hind's _Solar System_; the latter from Herschel's _Outlines of
Astronomy_.


TABLE I.--THE SATELLITES OF SATURN.

    +-----------+------------------------+---------------+
    |           |                        | MEAN APPARENT |
    |   NAME.   |  SIDEREAL REVOLUTION.  |   DISTANCE.   |
    +-----------+------------------------+---------------+
    |           | _d._  _h._  _m._  _s._ |      ´´       |
    | Mimas     |  0     22    37   22·9 |     26·78     |
    | Enceladus |  1      8    53    6·7 |     34·38     |
    | Tethys    |  1     21    18   25·7 |     42·57     |
    | Dione     |  2     17    41    8·9 |     54·54     |
    | Rhea      |  4     12    25   10·8 |     76·16     |
    | Titan     | 15     22    41   25·2 |    176·55     |
    | Hyperion  | 22     12?             |    213·3?     |
    | Japetus   | 79      7    53   40·4 |    514·52     |
    +-----------+------------------------+---------------+

The late Professor Bessel devoted much attention to the theory of
Titan, whose mean distance he found to be 20·706 equatorial radii of
the primary. Struve's measurements of the ring are given in the second
column of the following table. Sir John Herschel, however, regards
the Russian astronomer's interval between the rings as "somewhat too
small."[29] This remark is confirmed by the measurements of Encke,
whose results are given in column third. The fourth contains the
_mean_ of Struve's and Encke's measurements; and the fifth, the same,
expressed in equatorial radii of Saturn.


TABLE II.--THE RINGS OF SATURN.

  +---------------------+---------+---------+----------+------------+
  |                     |         |         |          |     IN     |
  |                     | STRUVE. |  ENCKE. |   MEAN.  | SEMI-DIAM. |
  |                     |         |         |          | OF SATURN. |
  +---------------------+---------+---------+----------+------------+
  | Equatorial radius   |    ´´   |   ´´    |   ´´     |            |
  |   of the planet     |  8·9955 |         |          |            |
  | Ext. semi-diameter  |         |         |          |            |
  |   of exterior ring  | 20·047  | 20·2225 | 20·13475 |   2·23830  |
  | Int. semi-diameter  |         |         |          |            |
  |   of exterior ring  | 17·644  | 18·0190 | 17·83150 |   1·98230  |
  | Ext. semi-diameter  |         |         |          |            |
  |   of interior ring  | 17·237  | 17·3745 | 17·30575 |   1·92380  |
  | Int. semi diameter  |         |         |          |            |
  |   of interior ring  | 13·334  | 13·3780 | 13·35600 |   1·48470  |
  | Breadth of interval | 00·407  | 00·6445 | 00·52575 |   0·05844  |
  +---------------------+---------+---------+----------+------------+

    The period of a satellite revolving at
      the distance, 1·9238, the interior
      limit of the interval                     =10h. 50m. 16s.
    One-sixth of the period of Dione            =10   56   53
    One-third        "         Enceladus        =10   59   22
    One-half         "         Mimas            =11   18   32
    One-fourth       "         Tethys           =11   19   36
    And the period of a satellite at the
      distance, 1·9823, the exterior
      limit of the interval                     =11   28    3

The interval, therefore, occupies precisely the space in which the
periods would be commensurable with those of the four members of the
system immediately exterior. Particles occupying this portion of the
_primitive_ ring would always come into conjunction with one of these
satellites in the same parts of their orbits. Such orbits would become
more and more eccentric until the matter moving in them would unite
near one of the apsides with other portions of the ring. _We have thus
a physical cause for the existence of this remarkable interval._



CHAPTER XIII.

THE ASTEROID RING BETWEEN MARS AND JUPITER.


The mean distances of the minor planets between Mars and Jupiter vary
from 2·20 to 3·49. The breadth of the zone is therefore 20,000,000
miles greater than the distance of the earth from the sun; greater
even than the entire interval between the orbits of Mercury and
Mars. Moreover, the _perihelion_ distance of some members of the
group exceeds the _aphelion_ distance of others by a quantity equal
to the whole interval between the orbits of Mars and the earth. The
_Olbersian_ hypothesis of the origin of these bodies seems thus
to have lost all claim to probability.[30] Professor Alexander's
theory of the disruption of a primitive discoidal planet of great
equatorial diameter, is less objectionable; still, however, it requires
confirmation. But whatever may have been the original constitution
of the ring,[31] its existence in its present form for an indefinite
period is unquestioned. Let us then consider some of the effects of
its secular perturbation by the powerful mass of Jupiter.

_Portions of the ring in which the periods of asteroids would be
commensurable with that of Jupiter._--The breadth of this zone is
such as to contain several portions in which the periods of asteroids
would be commensurable with that of Jupiter. As in the case of the
perturbation of Saturn's ring by the interior satellites, the tendency
of Jupiter's influence would be to form gaps or chasms in the primitive
ring.

    The mean distance of an asteroid whose period
      is 1/2 that of Jupiter                       =3·2776

    That of one whose period is 1/3 of Jupiter's   =2·5012
         "            "         2/5      "         =2·8245
         "            "         2/7      "         =2·2569
         "            "         3/7      "         =2·9574
         "            "         4/9      "         =3·0299

For the purpose of facilitating the comparison of these numbers with
the mean distances of the asteroids and of observing whether any order
obtains in the distribution of these mean distances in space, we have
arranged the minor planets, in the following table, in the consecutive
order of their periods:


Periods and Distances of the Asteroids.

    +------------+-------------+-----------+---------+
    |  ORDER OF  |    NAME.    | DISTANCE. | PERIOD. |
    | DISCOVERY. |             |           |         |
    +------------+-------------+-----------+---------+
    |      8     | Flora       |   2·2014  |  1193 d |
    |     43     | Ariadne     |   2·2034  |  1194·6 |
    |     72     | Feronia     |   2·2654  |  1245·4 |
    |     40     | Harmonia    |   2·2677  |  1247·3 |
    |     18     | Melpomene   |   2·2956  |  1270·4 |
    |     80     | Sappho      |   2·2971  |  1271·6 |
    |     12     | Victoria    |   2·3342  |  1302·6 |
    |     27     | Euterpe     |   2·3468  |  1313·2 |
    |      4     | Vesta       |   2·3613  |  1325·3 |
    |     84     | Clio        |   2·3618  |  1325·8 |
    |     30     | Urania      |   2·3655  |  1328·9 |
    |     51     | Nemausa     |   2·3657  |  1329·0 |
    |      9     | Metis       |   2·3858  |  1346·0 |
    |      7     | Iris        |   2·3863  |  1346·5 |
    |     60     | Echo        |   2·3931  |  1352·2 |
    |     63     | Ausonia     |   2·3949  |  1353·8 |
    |     25     | Phocea      |   2·4008  |  1358·8 |
    |     20     | Massilia    |   2·4144  |  1365·5 |
    |     67     | Asia        |   2·4217  |  1376·5 |
    |     44     | Nysa        |   2·4234  |  1378·0 |
    |      6     | Hebe        |   2·4244  |  1379·0 |
    |     83     | Beatrice    |   2·4287  |  1382·5 |
    |     42     | Isis        |   2·4400  |  1392·2 |
    |     21     | Lutetia     |   2·4411  |  1393·0 |
    |     19     | Fortuna     |   2·4416  |  1393·5 |
    |     79     | Eurynome    |   2·4437  |  1395·3 |
    |     11     | Parthenope  |   2·4519  |  1402·4 |
    |     17     | Thetis      |   2·4737  |  1421·1 |
    |     46     | Hestia      |   2·5262  |  1466·5 |
    |     89     |             |   2·5498  |  1487·2 |
    |     29     | Amphitrite  |   2·5544  |  1491·2 |
    |      5     | Astræa      |   2·5772  |  1511·2 |
    |     13     | Egeria      |   2·5775  |  1511·4 |
    |     14     | Irene       |   2·5860  |  1519·0 |
    |     32     | Pomona      |   2·5868  |  1519·6 |
    |     91     |             |   2·5958  |  1527·5 |
    |     56     | Melete      |   2·5959  |  1527·7 |
    |     70     | Panopea     |   2·6129  |  1543·0 |
    |     53     | Calypso     |   2·6188  |  1548·0 |
    |     78     | Diana       |   2·6236  |  1555·3 |
    |     23     | Thalia      |   2·6280  |  1568·0 |
    |     37     | Fides       |   2·6414  |  1570·0 |
    |     15     | Eunomia     |   2·6436  |  1572·6 |
    |     85     | Io          |   2·6466  |  1573·0 |
    |     50     | Virginia    |   2·6491  |  1575·0 |
    |     88     | Thisbe      |   2·6553  |  1580·0 |
    |     26     | Proserpina  |   2·6561  |  1581·1 |
    |     66     | Maia        |   2·6635  |  1587·8 |
    |     73     | Clytie      |   2·6666  |  1590·5 |
    |      3     | Juno        |   2·6707  |  1594·2 |
    |     75     | Eurydice    |   2·6707  |  1594·2 |
    |     77     | Frigga      |   2·6719  |  1595·3 |
    |     64     | Angelina    |   2·6805  |  1603·0 |
    |     34     | Circe       |   2·6865  |  1608·3 |
    |     58     | Concordia   |   2·7014  |  1622·0 |
    |     54     | Alexandra   |   2·7123  |  1631·6 |
    |     59     | Elpis       |   2·7131  |  1632·3 |
    |     45     | Eugenia     |   2·7218  |  1640·1 |
    |     38     | Leda        |   2·7401  |  1656·8 |
    |     36     | Atalanta    |   2·7458  |  1662·0 |
    |     71     | Niobe       |   2·7501  |  1665·8 |
    |     82     | Alcmene     |   2·7547  |  1670·0 |
    |     55     | Pandora     |   2·7591  |  1674·0 |
    |     41     | Daphne      |   2·7657  |  1679·9 |
    |      1     | Ceres       |   2·7663  |  1681·0 |
    |      2     | Pallas      |   2·7696  |  1683·5 |
    |     39     | Lætitia     |   2·7740  |  1687·6 |
    |     74     | Galatea     |   2·7777  |  1690·9 |
    |     28     | Bellona     |   2·7785  |  1691·6 |
    |     68     | Leto        |   2·7836  |  1696·3 |
    |     81     | Terpsichore |   2·8591  |  1765·7 |
    |     33     | Polyhymnia  |   2·8653  |  1770·6 |
    |     47     | Aglaia      |   2·8812  |  1786·4 |
    |     22     | Calliope    |   2·9092  |  1812·4 |
    |     16     | Psyche      |   2·9233  |  1826·0 |
    |     69     | Hesperia    |   2·9707  |  1871·1 |
    |     61     | Danaë       |   2·9837  |  1882·4 |
    |     35     | Leucothea   |   3·0040  |  1904·2 |
    |     49     | Pales       |   3·0825  |  1976·6 |
    |     86     | Semele      |   3·0909  |  1984·7 |
    |     52     | Europa      |   3·1000  |  1993·6 |
    |     48     | Doris       |   3·1094  |  2002·7 |
    |     62     | Erato       |   3·1297  |  2022·3 |
    |     24     | Themis      |   3·1431  |  2035·3 |
    |     10     | Hygeia      |   3·1512  |  2043·2 |
    |     31     | Euphrosyne  |   3·1513  |  2044·6 |
    |     57     | Mnemosyne   |   3·1565  |  2048·4 |
    |     90     | Antiope     |   3·1576  |  2049·4 |
    |     76     | Freia       |   3·3864  |  2276·2 |
    |     65     | Cybele      |   3·4205  |  2310·6 |
    |     87     | Sylvia      |   3·4927  |  2384·2 |
    +------------+-------------+-----------+---------+


REMARKS ON THE FOREGOING TABLE.

1. The first two members of the group, Flora and Ariadne, have very
nearly the same mean distance. Immediately exterior to these, however,
occurs a wide interval, including the distance at which seven periods
of an asteroid would be equal to two of Jupiter.

2. On the _outer_ limit of the ring Freia, Cybele, and Sylvia have also
nearly equal distances, and are separated from the next interior member
by a wide space including the distance at which two periods would be
equal to one of Jupiter, and also that at which five would be equal to
one of Saturn.

3. Besides these extreme members of the group, our table contains
eighty-six minor planets, all of which are included between the
distances 2·26 and 3·16; the mean interval between them being 0·0105.
The distances are distributed as follows:

    2·26 to 2·36   6   minimum.
    2·36 to 2·46  19   maximum.
    2·46 to 2·56   4   minimum.
    2·56 to 2·66  16 }
    2·66 to 2·76  16 } maximum.
    2·76 to 2·86   8
    2·86 to 2·96   4 } minimum.
    2·96 to 3·06   3 }
    3·06 to 3·16  10   maximum.

The clustering tendency is here quite apparent.

4. The three widest intervals between these bodies are--

    (_a_) between Leucothea and Pales   0·0785,
    (_b_)    "    Leto and Terpsichore  0·0755,
    (_c_)    "    Thetis and Hestia     0·0525;

and these, it will be observed, are the three remaining distances,
indicated on a previous page, at which the periods of the primitive
meteoric asteroids would be commensurable with that of Jupiter. Now,
if the original ring consisted of an indefinite number of separate
particles moving with different velocities, according to their
respective distances, those revolving at the distance 2·4935--in
the interval between Thetis and Hestia--would make precisely three
revolutions while Jupiter completes one. A planetary particle at this
distance would therefore always come in conjunction with Jupiter in
the same parts of its path: consequently its orbit would become more
and more eccentric until the particle itself would unite with others,
either exterior or interior, thus forming an asteroidal nucleus, while
the primitive orbit of the particle would be left destitute of matter,
like the interval in Saturn's ring.

5. If the distribution of matter in the zone was originally nearly
continuous, as in the case of Saturn's rings, it would probably break
up into a number of concentric annuli. On account, however, of the
great perturbations to which they were subject, these narrow rings
would frequently come in collision. After their rupture, and while
the fragments were collecting in the form of asteroids, numerous
intersections of orbits and new combinations of matter would occur, so
as to leave, in the present orbits, but few traces of the rings from
which the existing asteroids were derived. A comparison, however, of
the elements of Clytie and Frigga shows a striking similarity; and
Professor Lespiault has pointed out a corresponding likeness between
the orbits of Fides and Maia. For these four asteroids the nodal
lines and also the inclinations are nearly the same; while the periods
differ by only a few days. It is probable, therefore, that they are all
fragments of the same narrow ring. Finally, as they all move nearly in
the same plane, they must at some future time approach extremely near
each other, and perhaps become united in one large asteroid.



CHAPTER XIV.

ORIGIN OF METEORS--THE NEBULAR HYPOTHESIS.


In regard to the physical history of those meteoric masses which,
in such infinite numbers, traverse the interplanetary spaces, our
knowledge is exceedingly limited. Such as have reached the earth's
surface consist of various elements in a state of combination. It
has been remarked, however, by a distinguished scientist[32] that
"the character of the constituent particles of meteorites, and their
general microscopical structure, differ so much from what is seen
in terrestrial volcanic rocks, that it appears extremely improbable
that they were ever portions of the moon, or of a planet, which
differed from a large meteorite in having been the seat of a more or
less modified volcanic action." As the celebrated nebular hypothesis
seems to afford a very probable explanation of the origin of those
bodies, whether in the form of rings or sporadic masses, its brief
consideration may not be destitute of interest. We will merely premise
that the existence of true nebulæ in the heavens--that is, of matter
consisting of luminous gas--has been placed beyond doubt by the
revelations of the spectroscope.

As a group, our solar system is comparatively isolated in space; the
distance of the nearest fixed star being at least seven thousand times
that of Neptune, the most remote known planet. Besides the central or
controlling orb, it contains, so far as known at present, ninety-nine
primary planets, eighteen satellites, three planetary rings, and nearly
eight hundred comets. In taking the most cursory view of this system we
cannot fail to notice the following interesting facts in regard to the
motions of its various members:

1. The sun rotates on his axis from west to east.

2. The primary planets all move nearly in the plane of the sun's
equator.

3. The orbital motions of all the planets, primary and secondary,
except the satellites of Uranus and Neptune, are in the same
_direction_ with the sun's rotation.

4. The direction of the rotary motions of all the planets, primary and
secondary, in so far as has been observed, is identical with that of
their orbital revolutions; viz., from west to east.

5. The rings of Saturn revolve about the planet in the same direction.

6. The planetary orbits are all nearly circular.

7. The _cometary_ is distinguished from the _planetary_ portion of the
system by several striking characteristics: the orbits of comets are
very eccentric and inclined to each other, and to the ecliptic at all
possible angles. The motions of a large proportion of comets are _from
east to west_. The physical constitution of the latter class of bodies
is also very different from that of the former; the matter of which
comets are composed being so exceedingly attenuated, at least in some
instances, that fixed stars have been distinctly visible through what
appeared to be the densest portion of their substance.

None of these facts are accounted for by the law of gravitation. The
sun's attraction can have no influence whatever in determining either
the _direction_ of a planet's motion, or the eccentricity of its orbit.
In other words, this power would sustain a planetary body moving from
east to west, as well as from west to east; in an orbit having any
possible degree of inclination to the plane of the sun's equator, no
less than in one coincident with it; or, in a very eccentric ellipse,
as well as in one differing but little from a circle. The consideration
of the coincidences which we have enumerated led Laplace to conclude
that their explanation must be referred to the _mode_ of our system's
formation--a conclusion which he regarded as strongly confirmed by
the contemporary researches of Sir William Herschel. Of the numerous
nebulæ discovered and described by that eminent observer, a large
proportion could not, even by his powerful telescope, be resolved into
stars. In regard to many of these, it was not doubted that glasses
of superior power would show them to be extremely remote sidereal
clusters. On the other hand, a considerable number were examined which
gave no indications of resolvability. These were supposed to consist
of self-luminous, nebulous matter--the chaotic elements of future
stars. The great number of these irresolvable nebulæ scattered over
the heavens and apparently indicating the various stages of central
condensation, very naturally suggested the idea that the solar system,
and perhaps every other system in the universe, originally existed
in a similar state. The sun was supposed by Laplace to have been an
exceedingly diffused, rotating nebula, of spherical or spheroidal
form, extending beyond the orbit of the most distant planet; the
planets as yet having no separate existence. This immense sphere of
vapor, in consequence of the radiation of heat and the continual
action of gravity, became gradually more dense, which condensation was
necessarily attended by an increased angular velocity of rotation. At
length a point was thus reached where the centrifugal force of the
equatorial parts was equal to the central attraction. The condensation
of the interior meanwhile continuing, the equatorial zone was detached,
but necessarily continued to revolve around the central mass with
the same velocity that it had at the epoch of its separation. If
perfectly uniform throughout its entire circumference, which would be
highly improbable, it would continue its motion in an unbroken ring,
like that of Saturn; if not, it would probably collect into several
masses, having orbits nearly identical. "These masses should assume a
spheroidal form, with a rotary motion in the direction of that of their
revolution, because their inferior articles have a less real velocity
than the superior; they have therefore constituted so many planets in a
state of vapor. But if one of them was sufficiently powerful to unite
successively by its attraction all the others about its center, the
ring of vapors would be changed into one spheroidal mass, circulating
about the sun, with a motion of rotation in the same direction with
that of revolution."[33] Such, according to the theory of Laplace, is
the history of the formation of the most remote planet of our system.
That of every other, both primary and secondary, would be precisely
similar.

In support of the nebular hypothesis, of which the foregoing is a
brief general statement, we remark that _it furnishes a very simple
explanation of the motions and arrangements of the planetary system_.
In the first place, it is evident that the separation of a ring would
take place at the equator of the revolving mass, where of course the
centrifugal force would be greatest. These concentric rings--and
consequently the resulting planets--would all revolve _in nearly the
same plane_. It is evident also that the central body must have a
revolution on its axis _in the same direction with the progressive
motion of the planets_. Again: at the breaking up of a ring, the
particles of nebulous matter more distant from the sun would have
a greater absolute velocity than those nearer to it, which would
produce the observed _unity of direction in the rotary and orbital
revolutions_. The motions of the satellites are explained in like
manner. The hypothesis, moreover, accounts satisfactorily for the fact
that the orbits of the planets are all nearly circular. And finally,
it presents an obvious explanation of the rings of Saturn. It would
almost seem, indeed, as if these wonderful annuli had been left by the
Architect of Nature, as an index to the creative process.

The argument derived from the motions of the various members of the
solar system is not new, having been forcibly stated by Laplace,
Pontécoulant, Nichol, and other astronomers. Its full weight and
importance, however, have not, we think, been duly appreciated. That a
common physical cause has determined these motions, must be admitted
by every philosophic mind. But apart from the nebular hypothesis,
no such cause, adequate both in mode and measure, has ever been
suggested;--indeed none, it seems to us, is conceivable. The phenomena
which we have enumerated _demand_ an explanation, and this demand
is met by the nebular hypothesis. It will be found, therefore, when
closely examined, that the evidence afforded by the celestial motions
is sufficient to give the theory of Laplace a very high degree of
probability.

A comparison of the facts known in regard to comets, falling-stars,
and meteoric stones, seems to warrant the inference that they are
bodies of the same nature, and perhaps of similar origin; differing
from each other mainly in the accidents of magnitude and density. The
hypothesis of Laplace very obviously accounts for the formation of
planets and satellites, moving in the same direction, and in orbits
nearly circular; but how, it may be asked, can the same theory explain
the extremely eccentric, and in some cases retrograde, motions of
comets and aerolites? This is the question to which we now direct our
attention.

After the nuclei of the solar and sidereal systems had been established
in the primitive nebula, and when, in consequence, immense gaseous
spheroids had collected around such nuclei, we may suppose that about
the points of equal attraction between the sun and neighboring
systems, portions of nebulous matter would be left in equilibrio.
Such outstanding nebulosities would gradually contract through the
operation of gravity; and if, as would sometimes be the case, the solar
attraction should preponderate, they would commence falling toward our
system. Unless disturbed by the planets they would probably move round
the sun in parabolas. Should they pass, however, near any of the large
bodies of the system, their orbits might be changed into ellipses by
planetary perturbation. Such was the view of Laplace in regard to the
origin of comets.

It seems probable, however, that many of these bodies originated
_within_ the solar system, and belong properly to it. The outer rings
thrown off by the planets may have been at too great distances from the
primaries to form stable satellites. Such masses would be separated
by perturbation from their respective primaries, and would revolve
round the sun in independent orbits. Again: small portions of nebulous
matter may have been abandoned as primary rings, at various intervals
between the planetary orbits. At particular distances such rings would
be liable to extraordinary perturbations, in consequence of which
their orbits would ultimately assume an extremely elliptical form,
like those of comets, and perhaps also those of meteors. It was shown
in Chapter XIII. that several such regions occur in the asteroid zone
between Mars and Jupiter. We may add, in confirmation of this view,
that there are twelve known comets whose periods are included between
those of Flora and Jupiter. Their motions are all direct; their orbits
are less eccentric than those of other comets; and the mean of their
inclinations is about the same as that of the asteroids. These facts
certainly appear to indicate some original connection between these
bodies and the zone of minor planets.

The nebular hypothesis, it is thus seen, accounts satisfactorily for
the origin of comets, aerolites, fire-balls, shooting-stars, and
meteoric rings; regarding them all as bodies of the same nature, moving
in cometary orbits about the sun. In this theory, the zodiacal light is
an immense swarm of meteor-asteroids; so that the meteoric theory of
solar heat, explained in a previous chapter, finds its place as a part
of the same hypothesis.



CONCLUSION.


Some of the prominent results of observation and research in meteoric
astronomy may be summed up as follows:

1. The shooting-stars of November, August, and other less noted epochs,
are derived from elliptic rings of meteoric matter which intersect the
earth's orbit.

2. Meteoric stones and the matter of shooting-stars coexist in the
same rings; the former being merely collections or aggregations of the
latter.

3. The most probable period of the November meteors is thirty-three
years and three months. Leverrier's elements of this ring agree so
closely with Oppolzer's elements of the comet of 1866 as to render it
probable that the latter is merely _a large meteor_ belonging to the
same annulus.

4. The spectroscopic examination of this comet (of 1866) by William
Huggins, F.R.S., indicated that the nucleus was self-luminous, that
the coma was rendered visible by reflecting solar light, and that "the
material of the comet was similar to the matter of which the gaseous
nebulæ consist."

5. The time of revolution of the August meteors is believed to be about
105 years. M. Schiaparelli has found a striking similarity between the
elements of this ring and those of the third comet of 1862. The same
distinguished astronomer has shown, moreover, that a nebulous mass of
considerable extent, drawn into the solar system _ab extra_, would form
a _ring_ or _stream_.

6. The aerolitic epochs, established with more or less certainty, are
the following:

     1. February 15th-19th.
     2. March 12th-15th.
     3. April 10th-12th.
     4. April 18th-26th.
     5. May 8th-14th; or especially, 12th-13th.
     6. May 19th.
     7. July 13th-14th.
     8. July 26th.
     9. August 7th-11th.
    10. October 13th-14th.
    11. November 11th-14th.
    12. November 27th-30th.
    13. December 7th-13th.

About one-half of this number are also known as shooting-star epochs.

7. The epoch of November 27th-30th corresponds with that of the earth's
crossing the orbit of Biela's two comets. The aerolites of this epoch
may therefore have been moving in nearly the same path.

8. A greater number of aerolitic falls are observed--

    1. By day than by night.
    2. In the afternoon than in the forenoon.
    3. When the earth is in aphelion than when in perihelion.

The first fact is accounted for by the difference in the number of
observers; the second indicates that a majority of aerolites have
direct motion; and the third is dependent on the relative lengths of
the day and night in the aphelic and perihelic portions of the orbit.

9. The observed velocities of meteorites are incompatible with the
theory of their lunar origin.

10. If the meteoric swarm of November 14th has a period of thirty-three
years, Biela's comet passed very _near_, if not actually _through_ it
toward the close of 1845, about the time of the comet's separation. Was
the division of the cometary mass produced by the encounter?

11. The rings of Saturn may be regarded as dense meteoric masses, and
the principal or permanent division accounted for by the disturbing
influence of the interior satellites.

12. The asteroidal space between Mars and Jupiter is probably a wide
meteoric ring in which the largest aggregations are visible as minor
planets. In the distribution of the mean distances of the known members
of the group a clustering tendency is quite obvious.

13. The meteoric masses encountered by Encke's comet may account for
the shortening of the period of the latter without the hypothesis of an
ethereal medium.



APPENDIX.


A.

The Meteors of November 14th.

The _American Journal of Science and Arts_ for May, 1867 (received by
the author after the first chapters of this work had gone to press),
contains an interesting article by Professor Newton "On certain recent
contributions to Astro-Meteorology." Of the five possible periods of
the November ring, first designated by Professor N, it is now granted
that the longest, viz., 33-1/4 years, is most probably the true one.
The results of Leverrier's researches in regard to the epoch at which
this meteoric mass was introduced into the solar system, are given in
the same article. This distinguished astronomer supposes the group of
meteors to have been thrown into an elliptic orbit by the disturbing
influence of Uranus. The meteoric stream, according to the most
trustworthy elements of its orbit, passed extremely near that planet
about the year 126 of our era; which date is therefore assigned by
Leverrier as the probable time of its entrance into the planetary
system. This result, however, requires confirmation.

Although the earliest display of the November meteors, so far as
certainly known, was that of the year 902, several more ancient
exhibitions may, with some probability, be referred to the same epoch.
These are the phenomena of 532, 599, and 600, A.D., and 1768, B.C. (See
Quetelet's Catalogue.) The time of the year at which these showers
occurred is not given. The _years_, however, correspond very well
with the epochs of the maximum display of the November meteors. The
intervals arranged in consecutive order, are as follows:

  From B.C. 1768    to  A.D. 532,    69 periods of 33·319 years each.
    "  A.D.  532    to   "   599·5,   2     "      33·750      "
    "   "    599·5  to   "   902,     9     "      33·614      "
    "   "    902    to   "   934,     1     "      32·000      "
    "   "    934    to   "  1002,     2     "      34·000      "
    "   "   1002    to   "  1101,     3     "      33·000      "
    "   "   1101    to   "  1202,     3     "      33·667      "
    "   "   1202    to   "  1366,     5     "      32·800      "
    "   "   1366    to   "  1533,     5     "      33·400      "
    "   "   1533    to   "  1698,     5     "      33·000      "
    "   "   1698    to   "  1799,     3     "      33·667      "
    "   "   1799    to   "  1833,     1     "      34·000      "
    "   "   1833    to   "  1866,     1     "      33·000      "

The first three dates are alone doubtful. The whole number of intervals
from B.C. 1768 to A.D. 1866 is 109, and the mean length is 33·33 years.

The perturbations of the ring by Jupiter, Saturn, and Uranus, are
doubtless considerable. It is worthy of note that--

    14 periods of   Jupiter are nearly equal to  5 of the ring.
     9    "         Saturn     "           "     8       "
    23    "         Uranus     "           "    58       "

This group or stream has its perihelion at the orbit of the earth; its
aphelion, at that of Uranus. (See diagram, p. 24.) It must therefore
produce star-showers at the latter as well as at the former. Our
planet, moreover, at each encounter appropriates a portion of the
meteoric matter; while at the remote apsis of the stream Uranus in all
probability does the same. The matter of the ring will thus by slow
degrees be gathered up by the two planets.


B.

Comets and Meteors.

The recent researches and speculations of European astronomers in
regard to the origin of comets and of meteoric streams, have suggested
to the author the propriety of reproducing the following extracts from
an article written by himself, in July, 1861, and published in the
_Danville Quarterly Review_ for December of that year:

"Different views are entertained by astronomers in regard to the
_origin_ of comets; some believing them to enter the solar system _ab
extra_; others supposing them to have originated within its limits. The
former is the hypothesis of Laplace, and is regarded with favor by many
eminent astronomers. It seems to afford a plausible explanation of the
paucity of large comets during certain long intervals of time. In one
hundred and fifty years, from 1600 to 1750, sixteen comets were visible
to the naked eye; of which eight appeared in the twenty-five years from
1664 to 1689. Again, during sixty years from 1750 to 1810, only five
comets were visible to the naked eye, while in the next fifty years
there were double that number. Now, according to Laplace's hypothesis,
patches of nebulous matter have been left nearly in equilibrium in the
interstellar spaces. As the sun, in his progressive motion, approaches
such clusters, they must, by virtue of his attraction, move toward
the center of our system; the nearer portions with greater velocity
than the more remote. The nebulous fragments thus introduced into our
system would constitute comets; those of the same cluster would enter
the solar domain at periods not very distant from each other; the forms
of their orbits depending upon their original relative positions with
reference to the sun's course, and also on planetary perturbations. On
the other hand, the passage of the system through a region of space
destitute of this chaotic vapor would be followed by a corresponding
paucity of comets.

"Before the invention of the telescope, the appearance of a comet was
a comparatively rare occurrence. The whole number visible to the naked
eye during the last three hundred and sixty years has been fifty-five;
or a mean of fifteen per century. The recent rate of telescopic
discovery, however, has been about four or five annually. As many of
these are extremely faint, it seems probable that an indefinite number,
too small for detection, may be constantly traversing the solar domain.
If we adopt Laplace's hypothesis of the origin of comets, we may
suppose an almost continuous fall of primitive nebular matter toward
the center of the system--the _drops_ of which, penetrating the earth's
atmosphere, produce _sporadic_ meteors; the larger aggregations forming
comets. The disturbing influence of the planets may have transformed
the original orbits of many of the former, as well as of the latter,
into ellipses. It is an interesting fact that the motions of some
luminous meteors--or _cometoids_, as perhaps they might be called--have
been decidedly indicative of an origin beyond the limits of the
planetary system.

"But how are the phenomena of _periodic_ meteors to be accounted for,
in accordance with this theory?

"The division of Biela's comet into two distinct parts suggests several
interesting questions in cometary physics. The nature of the separating
force remains to be discovered; 'but it is impossible to doubt that it
arose from the divellent action of the sun, whatever may have been the
mode of operation.'

"'A signal manifestation of the influence of the sun,' says a
distinguished writer, 'is sometimes afforded by the breaking up
of a comet into two or more separate parts, on the occasion of its
approach to the perihelion. Seneca relates that Ephoras, an ancient
Greek author, makes mention of a comet which before vanishing was
seen to divide itself into two distinct bodies. The Roman philosopher
appears to doubt the possibility of such a fact; but Keppler, with
characteristic sagacity, has remarked that its actual occurrence was
exceedingly probable. The latter astronomer further remarked that there
were some grounds for supposing that two comets, which appeared in the
same region of the heavens in the year 1618, were the fragments of a
comet that had experienced a similar dissolution. Hevelius states that
Cysatus perceived in the head of the great comet of 1618 unequivocal
symptoms of a breaking up of the body into distinct fragments. The
comet when first seen in the month of November, appeared like a round
mass of concentrated light. On the 8th of December it seemed to be
divided into several parts. On the 20th of the same month it resembled
a multitude of small stars. Hevelius states that he himself witnessed a
similar appearance in the head of the comet of 1661.'[34] Edward Biot,
moreover, in his researches among the Chinese records, found an account
of 'three dome-formed comets' that were visible simultaneously in 896,
and pursued very nearly the same apparent path.

"Another instance of a similar phenomenon is recorded by Dion Cassius,
who states that a comet which appeared eleven years before our era,
separated itself into several small comets.

"These various examples are presented at one view, as follows:

    "I. Ancient bipartition of a comet.--_Seneca, Quæst. Nat._,
    _lib. VII. cap. XVI._

    "II. Separation of a comet into a number of fragments, 11
    B.C.--_Dion Cassius._

    "III. Three comets seen simultaneously pursuing the same orbit,
    A.D. 896--_Chinese records--Comptes Rendus_, tom. xx. 1845, p.
    334.

    "IV. Probable separation of a comet into parts, A.D.
    1618.--_Hevelius_, _Cometographia_, p. 341.--_Keppler_, _De
    Cometis_, p. 50.

    "V. Indications of separation, 1661.--_Hevelius_,
    _Cometographia_, p. 417.

    "VI. Bipartition of Biela's comet, 1845-6.

"In view of these facts it seems highly probable, if not absolutely
certain, that the process of division has taken place in several
instances besides that of Biela's comet. May not the force, whatever
it is, that has produced _one_ separation, again divide the parts? And
may not this action continue until the fragments become invisible?
According to the theory now generally received, the periodic phenomena
of shooting-stars are produced by the intersections of the orbits of
such nebulous bodies with the earth's annual path. Now there is reason
to believe that these meteoric rings are very elliptical, and in this
respect wholly dissimilar to the rings of primitive vapor which,
according to the nebular hypothesis, were successively abandoned at
the solar equator; in other words, that the matter of which they are
composed moves in _cometary_ rather than _planetary_ orbits. May not
our periodic meteors be the _debris_ of ancient but now disintegrated
comets, whose matter has become distributed around their orbits?"


C.

Biela's Comet and the Meteors of November 27th-30th.

At the close of Chapter IV. it was suggested that the meteors of
November 27th-30th might possibly be derived from a ring of meteoric
matter moving in the orbit of Biela's comet. Since that chapter was
written similar conjectures have been started in the _Astronomische
Nachrichten_[35] by Dr. Edmund Weiss and Prof. d'Arrest. The latter
attempts to show that the December meteors may be derived from the same
ring. The question will doubtless be decided at no distant day.


D.

The First Comet of 1861 and the Meteors of April 20th.

Recent investigations render it probable that the orbit of the first
comet of 1861 is identical with that of the meteors of April 20th. The
orbit is nearly perpendicular to the ecliptic.



FOOTNOTES:


[1] For a full description, see Silliman's Journal for January and
April, 1834 (Prof. Olmsted's article). Also a valuable paper, in the
July No. of the same year, by Prof. Twining.

[2] Physique du Globe, Chap. IV.

[3] Professor Olmsted estimated the number of meteors, visible at New
Haven, during the night of November 12th-13th, 1833, at 240,000.

[4] Conde says, "there were seen, as it were lances, an infinite number
of stars, which scattered themselves like rain to the right and left,
and that year was called 'the year of stars.'"

[5] In 1202, "on the last day of Muharrem, stars shot hither and
thither in the heavens, eastward and westward, and flew against
one another like a scattering swarm of locusts, to the right and
left; this phenomenon lasted until daybreak; people were thrown
into consternation, and cried to God the Most High with confused
clamor."--Quoted by Prof. Newton, in Silliman's Journal, May, 1864.

[6] Am. Journ. of Sci. and Arts, May and July, 1864.

[7] The stream or arc of meteors is several years in passing its node.
The first indication of the approach of the display of 1866 was the
appearance of meteors in unusual numbers at Malta, on the 13th of
November, 1864. The great length of the arc is indicated, moreover, by
the showers of 931 and 934.

[8] Silliman's Journ. for Sept. and Nov., 1861.

[9] The numerical results here given are those found by Professor
Newton. See Silliman's Journ. for March, 1865.

[10] The diameters of the asteroids are derived from a table by Prof.
Lespiault, in the Rep. of the Smithsonian Inst. for 1861, p. 216.

[11] "It appears probable, from the researches of Schreibers, that 700
fall annually."--Cosmos, vol. i. p. 119 (Bohn's Ed.). Reichenbach makes
the number much greater.

[12] New Concord is close to the Guernsey County line. Nearly all the
stones fell in Guernsey.

[13] Cosmos, vol. i. p. 120.

[14] Leverrier's Annals of the Observatory of Paris, vol. i. p. 38.

[15] "This is a remarkable example of a stone arriving on the earth
with a temperature approaching that of the interplanetary spaces.
Aerolites containing much iron, a substance which conducts heat well,
get thoroughly heated by their passage through the atmosphere. But the
stony aerolites, containing less iron, conducting heat badly, preserve
in their interior the temperature of the locality from which they fall;
their surface only is heated, and generally fused. When the stones are
large, the _excessive cold_ of their interior portion, which must be
nearly that of interplanetary space, is remarked; but when small, they
remain hot for some time."--_Dr. Phipson._

[16] Silliman's Journal, September, 1864.

[17] The same explanation is given by T. M. Hall, F.G.S., in the
Popular Science Review for Oct. 1866.

[18] This list contains nothing but _aerolites_. In the Edinburgh
Review for January, 1867, we find the following statements: "Out of
the large number of authentic aerolites preserved in mineralogical
collections, two only--one on the 10th of August, and one on the 13th
of November--are recorded to have fallen on star-shower dates. On the
other hand, five or six meteorites, on the epoch of the 13th-14th of
October, belong to a date when star-showers, so far as is at present
known, do not make their appearance." The inaccuracy of the former
statement is sufficiently apparent. In regard to the latter we remark
that Quetelet's Catalogue gives one star-shower on the 14th of October,
and another on the 12th.

[19] The date of this remarkable occurrence is worthy of note as a
probable aerolite epoch. From the 12th to the 15th of March we have the
following falls of meteoric stones:

    1. 1731, March 12th. At Halstead, Essex, England.
    2. 1798, March 12th. At Salés, France.
    3. 1806, March 15th. At Alais, France.
    4. 1807, March 13th. At Timochin, Russia.
    5. 1811, March 13th. At Kuleschofka, Russia.
    6. 1813, March 13th-14th. The phenomena above described.
    7. 1841, March 12th. At Grüneberg, Silesia.

Numerous fire-balls have appeared at the same epoch.

[20] The innermost or semi-transparent ring of Saturn appears to be
similarly constituted, as the body of the planet is seen through it
without any distortion whatever.

[21] Origin of the Stars, p. 173.

[22] Origin of the Stars, p. 184.

[23] Since the above was written Prof. Ennis has informed the author
that, without making any estimate of his own, he adopted the density of
Jupiter's first satellite as given in Lardner's _Handbook of Astronomy_.

[24] Origin of the Stars, p. 77.

[25] Youman's Correlation and Conservation of Forces, p. 244.

[26] Iowa Instructor and School Journal for November, 1866, p. 49.

[27] A recent hypothesis in regard to the temporary star of 1572 has
been proposed by Alexander Wilcocks, M.D., of Philadelphia. See Journ.
Acad. Nat. Sci. of Phila. for 1859.

[28] Gautier's Notice of Recent Researches relating to
Nebulæ.--Silliman's Journal for Jan. 1863, and March, 1864.

[29] Outlines of Astronomy, Art. 442.

[30] A learned and highly interesting examination of this hypothesis
will be found in a memoir "On the Secular Variations and Mutual
Relations of the Orbits of the Asteroids," communicated to the Am.
Acad. of Arts and Sciences, April 24th, 1860, by Simon Newcomb, Esq.

[31] For an explanation of the origin of the asteroids according to
the nebular hypothesis, see an article by David Trowbridge, A.M., in
Silliman's Journal for Nov. 1864, and Jan. 1865.

[32] H. C. Sorby, F.R.S.

[33] Harte's Trans. of Laplace's Syst. of the World, vol. ii., note vii.

[34] Grant's Hist. of Phys. Astr., p. 302.

[35] Nos. 1632 and 1633.



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Transcriber's Notes:


Punctuation and spelling were made consistent when a predominant
preference was found in this book; otherwise they were not changed.

Simple typographical errors were corrected; occasional unbalanced
quotation marks retained.

Ambiguous hyphens at the ends of lines were retained.

Text uses both "star shower" and "star-shower"; not changed here.

"Keppler" is spelled that way in this text.





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