Title: New Edition of Hints on Silver-Glass Reflecting Telescopes Manufactured by Mr. G. Calver, F.R.A.S. - with Directions for Silvering, Adjusting, &c.
Author: Calver, George
Language: English
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      NEW EDITION OF HINTS ON Silvered-Glass Reflecting TELESCOPES

      MANUFACTURED BY

      MR. G. CALVER, F.R.A.S.

      WITH DIRECTIONS FOR SILVERING, ADJUSTING, &c.

      1877.


      GEORGE CALVER,

          HILL HOUSE, WIDFORD,

              CHELMSFORD, ESSEX.


[ Illustration: decorative ]



      HINTS ON Silvered-Glass Reflecting Telescopes.


Of the various forms of Telescopes now in use, each has its own
peculiar advantages; but the Silvered-Glass Reflector is undoubtedly
gaining favour among our practical observers. A well-figured
speculum, being perfectly free from chromatic aberration, gives, in
a proper condition of the atmosphere, the finest possible definition
of the Moon and planets, the markings and colours of these objects
being excellently seen; while coloured stars, such as Albireo (β
Cygni), or Almaach (γ Andromedæ), are exceedingly well shown, the
beautiful contrast of the stars in the former being especially
noticeable in a reflector. The advice of “F.R.A.S.” (in the “English
Mechanic,” March 21st, 1873) as to the choice of a Telescope, may
here appropriately be quoted. After expressing a preference for
refractors when measuring close double-stars, he says, “But should
the object of your correspondent be merely to regard the wonders and
beauties of the Heavens, or notably, should he purpose to devote
himself to the study of the physical structure of the Moon and
planets, then by all means let him obtain the largest reflector he
can afford; its absolute achromatism tells most astonishingly on
these last-named objects.” This is the opinion of one who has great
practical knowledge of the different forms of Telescopes.

If Achromatic Telescopes of large aperture could be made as cheaply
as reflectors, and in as convenient a form, they would doubtless be
preferred for general star-work, although the aberrations,
especially that of colour, cannot be so perfectly corrected. A
silvered-glass reflector is, however, much cheaper than a refractor,
and, when the aperture exceeds five or six inches, is much handier
to work, and occupies less space, being only about half the length
of an achromatic of the same aperture. It is true that a reflector
will give less light than an achromatic of equal aperture—but this
is, in certain conditions of the atmosphere, a distinct advantage,
the extra aperture to give the same light adding to the definition
and penetrating power. An example of this is seen in the beautiful
definition given by an unsilvered mirror on brilliant objects, as
the Sun, Moon, and Venus. In large achromatics, the distressing
excess of light has often to be reduced by diminishing the aperture
or using a higher power than is convenient; and in such cases a
lower and more suitable power can be employed with a reflector.

When the air is unsteady, the definition of Reflectors, owing to
their tubes being open, is more liable to fluctuate than that of
refractors, although when a reflector does not give good definition
on account of the atmosphere, a refractor of the same aperture will
certainly not perform satisfactorily. Sir John Herschel has shown
that when the air in the tube of even an achromatic is disturbed in
turning from one object to another, good definition does not return
until it is brought to rest. In order to reduce the vibration of the
air in the open tube, and also that of the stand, to a minimum,
reflectors require to be very firmly and steadily mounted, and to
have iron tubes.

Many of the specula made by me are now in observatories, where they
have been compared with achromatics of first-rate quality with the
most satisfactory results. For instance, several 6-1/2 inch specula
were tried with two excellent achromatics of 4-1/2 and 6 inches
aperture, when the planetary definition was considered to be
superior with the reflectors; and the appearance of the star-discs,
with equal apertures, differed little from the beauty and hardness
of the images given by the achromatics. In viewing stars of great
altitude, the use of the refractor is extremely inconvenient to the
observer, whose position is necessarily very uncomfortable, while
with the Newtonian reflector any part of the heavens may be observed
with the same ease and comfort. In short, a good speculum, well
mounted and situated, is sure to be both pleasing and satisfactory.

It is perhaps unnecessary to remind the reader that, when the
defining powers of a telescope are put to the test, as much depends
on the acuteness of the observer’s eye and the practice he has had,
as upon the perfection of the instrument and the fineness of air. It
is a mistake to suppose that when the stars appear to be the
brightest to the unaided eye, definition will be at its best, though
this may happen; when it does so, the astronomer should make the
most possible use of the opportunity, as such nights are very
scarce. As a rule, the best nights are those when there is the
slightest possible mistiness of the atmosphere, and for the faintest
stars absence of bright moonlight. The 5 inch mirror is guaranteed
to divide stars one second apart with ease, and closer ones in very
fine air. The 8-1/2 will split such difficult pairs as γ^2
Andromedæ, and μ^2 Boötis. An acute eye will master these stars with
even a less aperture on very favourable occasions, γ^2 Andromedæ
having been seen with a 7-inch stop of a 10-inch mirror, and Mr.
Sadler, of Honiton Rectory, has split this star with his 6-1/2-inch
telescope. It sometimes happens on favourable nights that the most
difficult objects will be seen with the same telescope, which on
other occasions had failed to show them as well as a much smaller
aperture had done in very fine air. These remarks equally apply to
the observation of minute stars and planetary detail. The amateur
must follow the advice of the Rev. T. W. Webb, given in “Celestial
Objects” (pages 15-17), and must cultivate that virtue applicable to
all scientific investigation, namely, patience. The following
interesting and difficult objects may be looked for, the powers used
for their observation should vary from 150 to 300, and for the very
closest stars up to 500, or even still higher.


      TESTS FOR SPECULA.

LIGHT TESTS.

  94 Ophiuchi. 5″ : 7, 13.
  58 Ceti. 3″·5 : 6·5, 14.
  γ Crateris. 3″ : 4, 14.
  15 Monocerotis. 25″, 15″ : 6, 9·5, 15.
  τ Orionis. 15″, 20″ : 4, 15, 12.
  υ Ceti. 6″ : 4·5, 15.
  ε Trianguli. 5″ : 5·5, 15.
  179 Piscium. 3″ : 8·5, 15.
  110 Herculis. 55″ : 5, 16.
  μ Andromedæ. 45″ : 4, 16.
  β Equulei. 35″, 3″, 50″ : 5, 13, 16, 14.
  85 Virginis. 30″ : 6, 16.
  55 Andromedæ. 25″ : 5·5, 16.
  178^a Delphini. 20″ : 7·5, 16.
  212 Libræ. 20″, 10″ : 6, 16, 8.
  14 Monocerotis. 10″ : 6, 16.
  94 Ceti. 5″ : 5·5, 16.
  δ Aquilæ. 1″·5 : 3·5, 16.


SEPARATING TESTS.

  33 Orionis. 2″ : 6, 8.
  52 Orionis. 1″·8 : 6, 8.
  δ Cygni. 1″·8 : 3·5, 9.
  2 Camelopardi. 1″·7 : 5·5, 7·5.
  π Aquilæ. 1″·7 : 6, 7.
  σ^2 Cancri. 1″·4 : 5·5, 7.
  9 Leonis. 1″·2 : 7·5, 7·5.
  η Orionis. 1″ : 4, 5.
  ε Arietis. 1″ : 5, 6·5.
  4 Lyncis. 1″ : 6, 7·5.
  37 Pegasi. 0″·8 : 6, 7·5.
  749ξ Tauri. 0″·8 : 7·1, 7·2.
  46 Arietis. 0″·8 : 8, 9.
  λ^a Cygni. 0″·7: 5, 6.
  β Delphini. 0″·7 : 5, 5·5.
  20 Draconis. 0″·7 : 7, 7·5.
  287 Draconis. 0″·7 : 7, 8.
  178^b Delphini. 0″·6 : 4·5, 6.
  φ Draconis. 0″·6 : 4·5, 6·5.
  γ^2 Andromedæ. 0″·6 : 8·5, 9.
  μ^2 Boötis. 0″·5 : 8, 8·5.
  ι^a Boötis. 0″·5 : 4·5, 4·5.
  7 Tauri. 0″·5 : 6, 6·5.
  108 Draconis. 0″·5 : 9, 9.
  η Herculis. 0″·3 : 3, 8.
  42 Comæ Berenices. 0″·3 : 4·5, 5.
  ω Leonis. 0″·3 : 6·5, 7·5.


Since writing the first edition of my catalogue, the writer has
received many gratifying accounts of the success of the
“Silvered-Glass Reflector.” Many private letters have been received
by him from observers, expressing their delight and satisfaction.
This has been so encouraging that no pains have been spared, nor any
opportunities neglected, in turning to the best purpose every
valuable lesson that continued practice and experience may have
suggested in the manipulation of specula from time to time, in order
to secure the best means for obtaining the highest excellence of
defining power.

Many modifications and improvements have been made in working and
testing mirrors, and special machinery and appliances constructed
for large sizes. But to complete my conditions suitable for truly
figuring and testing specula of considerable size, I found it
necessary to remove from the traffic and tremor of a town to a still
and tranquil situation in the country.

The truth of the curve is so sensibly and seriously affected by
vibration constantly going on in and near a town, that it is liable
to a variety of defects, and the surface becomes wavy and “plucked.”

As an instance, I may mention that my first and most convincing
proof of the advantage of the stiller situation was tested by an
18-inch speculum (on which much labour had been bestowed); it was
laid aside, but successfully finished after removal, and without
undulations or any perceptible defect, and the Observer wrote me,
that in good air, he “saw Sirius as a brilliant white dot, without a
ray or appendage of any kind, and celestial photographs obtained
with it are very fine.” Such results were exceedingly gratifying, as
they were obtained with much less labour and uncertainly, and the
tedious process of the final touches had not to be repeated so many
times.

It is said that the celebrated Alvan Clarke, from the same effects
of tremor, never finished an object-glass to his satisfaction
above-ground; and Dr. Draper, testing his mirrors at the centre of
curvature, to avoid draughts, &c. in an ordinary apartment, resorts
to an underground one.

In this little book of “Hints” it may be useful to remind those who
possess a speculum of fine quality that they are not produced by a
“rule of thumb”—so to speak—and that the difference between _a_
speculum and a really _fine_ one, giving a maximum of defining and
illuminating power, is the result of considerable labour and
thought, and deserves careful usage.

The Rev. Cooper Key, an amateur of much experience, writes in the
“English Mechanic,” that he was eight months (working sometimes
eight hours a day), giving his 18 inch speculum its final touches
and corrections.

A well known correspondent of the “English Mechanic,” “Hyperion,”
tells us he found it impossible to test his 8-1/2 inch mirror in an
ordinary room, and had to resort to a tunnel under the clay of his
garden. Those who have the means and perseverance to make their own
mirror, should be careful not to proceed with the finishing touches
until an hour at night when their workshop, if in a town, is free
from tremor.

First secure a well-ground and carefully-centred disc, let the
polish be as perfect as possible before any attempt is made to
figure. Care must be taken that every square or portion of the
polisher is of the same consistency and temperature, that the disc
may not be acted on irregularly.

To give the pitch this quality it must be well boiled and “pulled,”
so that no air bubbles are in the squares, as these cause expansion
or contraction as the temperature of the apartment varies, or that
of the pitch and glass from friction.

It is much the best plan to keep the workshop to the same uniform
temperature as the polisher was made for, allowing no draughts to
pass over the mirror while working, nor the gas or lamp to be near.
When the polisher is warmed—which it should be after laying aside
for any time—it should be warmed _equally_. Neglect of the above in
making the polisher, or any incautious handling of either the disc
or polisher, will be sure to cause defects, which cannot be cured
but by retracing the early steps in the fine grinding with an
accurately centered tool.

The polishing successfully accomplished, the process of correcting
for parallel rays is next proceeded with. At every step all possible
care must be taken to prevent the mirror from running into an
irregular curve. The importance of this cannot be too strongly
urged, if a speculum capable of doing the _best_ work is desired, as
the curve _must_ be true, regular, or uniform, to give the _highest_
defining and illuminating power. An under-corrected mirror, if of a
regular curve, will perform much better than a compound correction,
exhibiting at the focal point much less lateral aberration.

A brief explanation of this may be of use as far as the limits of
these pages will admit. It would be impossible to teach, by a mere
description of methods, how to commence and finish off a speculum of
good quality, even if every working secret and minute detail were
unreservedly explained. The only way is to master sufficient theory,
and the rest will come by prolonged care and perseverance. I state
this because amateurs who have been desirous of enjoying the
gratification of observing with a mirror of their own making have
written for information which they have been quite willing even to
pay for liberally, but have felt disappointed, and perhaps thought
it somewhat discourteous, on being told that what they wanted was
impracticable and could not be satisfactorily attempted by the
Optician in writing. In some cases I have finished amateurs’ work on
agreeable terms, and which has led to a pleasant correspondence or
acquaintance. These remarks may prevent some future disappointment.

Every one is familiar with the fact that the parabola is the only
concave surface that can reflect rays of light falling on its
surface from an object at an infinite distance—such as the stars and
planets practically are—to one common focus, or without aberration.
This series or column of rays (which is equal in diameter to the
opening of the speculum), reach the mirror without making an angle
to it or to each other, they travel side by side, they are all of
one length, and are reflected to a point, and are therefore all of
the same length at the proper focal distance, viz., half the radius
of the curvature of the concave. The properties of the parobola make
the nearest possible approach to it of the utmost importance.

It has been said that a considerably under-corrected surface, if of
a true and uniform curve, is better than one with less aberration,
with zones or sections of various curves. To explain this, let us
suppose an artificial star at some short distance, say 50 yards, the
parabola would not form an image of this at the eye-piece without
aberration; it has for this distance too short a focus for the
central rays, and the best disc is inclined to the inner focus,
because the rays from the object _diverge_ towards it, instead of
travelling parallel; and they reach the surface (the central rays
compared with the marginal), at an angle equal to the semi-diameter
of the mirror.

But, if instead of a parabolic mirror an elliptical one be used,
which has one of its foci at 50 yards’ distance, the image will be
perfect. Now place the artificial star at 500 yards, the image will
now be attended with perceptible aberration. The longer focus of the
ellipse must be worked further and further from the mirror by
shortening the focus of the central rays. Correct it for this
distance, and again remove the artificial star to a still greater
distance, repeating the corrections as before and carrying the outer
focus towards the object, and the inner towards the mirror, until
the rays from the object become more and more parallel, and the
curve is nearer and nearer to the parabola, or that eccentricity of
ellipse which acts better and better for distant objects or parallel
rays.

It is evident from this that if the ellipse is corrected very
considerably towards the parabola, without irregularities, and
_every part_ of the surface corrected regularly from the centre to
the edge (no part hastening more than another), that such a surface,
though under-corrected, is much better than if one portion is fully
and another under-corrected, especially if the more imperfect
portion is towards the edge. Such a compound correction may show
little or no _outstanding_ aberration at the focal point, but the
rays do not find a focus at the same regular pace as they would from
a regular curve—one edge of a zone will be coming into focus when
another would be going out. With the focussing screw they are
focussed to the place where they appear to collapse, and are most
satisfactory, though, _in reality_, the rays at the best place bend
over each other, and the definition is imperfect. From a star, which
is only a point, this may be more tolerated, but on the planets,
where the image has a sensible diameter, and is perhaps magnified
many times, this imperfect curve is very inferior to the regular
one, whose error is all of _one kind_. The light is all there
_somewhere_, but not with any good effect. There is no _proper_
illumination or definition, as rays are employed which are crossing
the optical axis at _varying_ angles, and the result is confusion.

So the amateur who sets himself the pleasant task of making his own
speculum (for there are many who can better afford the labour than
the capital to purchase, and whose capabilities are thus superior to
their means), need not be discouraged and give up the pursuit
because he cannot obtain the best results by getting a perfectly
parabolic glass. But if he has been successful in removing a
considerable amount of the spherical error, and advanced to the
elongated ellipse by maintaining a truthful curve, “let well alone”
with this disc, and proceed no further, but commence _another_,
taking care not to alter the first until the second is _better_, and
_then_ an improvement of the first may be attempted.

In the second attempt, should the amateur lose control over the
_regularity_ of the surface, let him try it as an experiment against
the first on the planets, and he will not fail to appreciate the
difference, and will be stimulated by fresh courage to get as near
to the parabola as possible with the same accurate curve.

To produce a true and uniform curve is, however, the acme of
troubles, whether it is desired to obtain the spherical, or
parabola, or any other curve. It is generally supposed that the
spherical curve is a very easy matter, so easy indeed that it is
difficult to avoid. This is a very great mistake—a spherical curve
of undeviating truth is as difficult a problem as a true parabola.
The spherical curve is the _only uniform_ curve, it has but _one_
focus, and the polisher must coincide with, and be of the same
radius as the glass, at every instant. This is why the optician
strives to obtain a semi-polish with the grinder to lessen the risk
of losing his curve on the polisher, for the curves of an object
glass are spherical. The curve most liable to be obtained by the
amateur is the spheroidal, a curve with its marginal rays _shorter_
than the central, or half the radius of curvature.

There are no means with the _telescope_ of telling the spheroidal,
approximating to the sphere, _from_ the sphere. There are _no_ means
of analyzing the exact character of a curve _equal_ to certain
methods at the centre of the curvature, but to accomplish this
requires much practice and observation, with “surroundings”
perfectly free from vibration. If the amateur can overcome this, and
lives in or very near a town, he should only work at the polishing
and figuring during the late hours of the night, when traffic, &c.
have subsided. Then, by carefully preventing any draughts in the
apartment, and with the mirror of the same temperature as the air in
the room, he will then be able to see how varied and numerous are
the chances of error in working a mirror, and the great care
necessary to avoid or cure them. He will find the surface
exceedingly prone to receive zones and irregularities during work,
and much more so than to “work true.”

The necessity for avoiding incautious handling or heating may be
realized by the following little experiment when one can manage and
understand it:—Place the tip of one finger on the surface, as it
hangs in the dark room ready for testing, and with very gentle
pressure let it remain long enough to spell one’s name; it will then
be seen that the feeble heat of the finger has, by expansion, raised
a mound on the surface of the glass, and though this amount of
swelling must be _very_ small, yet it is enough to cast a shadow
across the surface, as if something were laid on it, and quite ten
minutes will elapse before the heat will leave this spot and the
surface again become level. Now if the polisher were placed on the
glass while this hillock was there, a permanent hollow would be the
result. For a full account of these methods (of which Foucault was
the discoverer) the reader is referred to Sir John Herschel’s and
Dr. Draper’s works on the telescope.

Care must be taken not to leave too much aberration, as then the
central disc is formed too positively outside the focus, and the
rest of the light from the object appears as obtrusive rings and
false light. The over-correction is bad, and acting as a negative
lens the disc is formed too near the mirror. Such a correction,
besides being objectionable on almost all classes of objects,
prevents the use of the “Barlow” lens, and acts badly with all kinds
of positive or Ramsden eye-pieces, which improve _under_-corrected,
but “make bad worse” with over-corrected surfaces.

If these few and brief hints should stimulate the industrious and
persevering student to make his own telescope, and thus enjoy the
fruits of his own labours (which may add a relish and a pleasure to
his astronomical work), they will have served the purpose for which
they are written.

After a “Hint” on the choice of focus for the mirror, it only
remains to say a few words about the plane, as this, with the large
speculum, are the only parts that need be home-made as far as the
optical work is concerned. Never adopt a “dumpy” for general use
where high powers are sometimes wanted, for small and moderate
sizes, say 8 to 12 diameters, and for large sizes not less than
about 6 diameters of the mirror, as the larger ones practically
admit of a shorter focus. The short ones can be mounted somewhat
cheaper, but never choose them on _this_ account, they will not make
so satisfactory an instrument, and no adaptation of “Barlow’s” will
make it so.

To make the plane, provide three well-turned metal discs of 7 inches
or 9 inches diameter. Iron is the best, as the work will go down
closer, and the plates or discs may be very thick—say an inch—and
not so liable to “spring.” These turned discs must be scraped and
ground perfectly flat on each other, until they are in good contact
all over, so that there is nothing between the faces when testing
them. In the earlier stage of “truing,” oil and colour can be used.
When these discs are proved true, a disc of plate glass, same size,
is cemented with pitch on one of them, or on a thick disc of glass,
and care must be taken that it is not strained while on the block
during working. Truly grind this plate on one of the tools to a fine
semi-polish. Polish on the same tool with a piece of thick silk or
alpaca, laid over and cemented down by a solution of resin dissolved
in turpentine (as much resin as the turpentine will dissolve), then,
with the tip of the finger, thinly smear over the tool and bind
round the edge with cord, and the silk will keep in place. Fill up
the texture of the silk or alpaca evenly with damp rouge, keep it
uniformly damp, and never let the rouge and water work about. It may
be polished on very hard strained pitch, but pitch for the amateur
is not so safe, as it is liable in his hands to alter its form and
destroy the truth of the plane, but it is the quickest and handiest
if it can be managed.

After the polish is _perfect_ remove the plate from the support and
cut into squares a little larger than the size of the intended flat.
Test these in the telescope on a _star_. If one plane turns out bad,
the whole will most likely be so, and another plate must be worked
with renewed energy and care, for a bad plane will spoil the action
of the speculum however good, for there is no way of counteracting
the curved surface of the flat or second reflector. The edge of the
plate for about an inch should not be used.

When a good plane is found it can be edged by turning a piece of
wood a little less in diameter than the minor axis of the plane
required, turn the end square, and mark a line around it distant
from the end equal to the diameter, and cut through to the opposite
edge, and it will give the oval and will appear round at 45°, this
will mount nicely in brass tubes of the proper size, and a cover
should be made to fit easy.


      “THE EQUATORIAL.”

Fig. 1 is a modification of the German principle, and it should be a
sufficient recommendation to remark that it is the principle used by
a maker of such experience as Mr. John Browning, and is, without
doubt, the very best style of mounting for a fixed equatorial,
especially when clockwork is employed, because clock power is
applied to the polar axis itself direct from the driving worm.

The driving part, viz., the worm and wheel, which is out of the
observer’s way (being between the standards), is not liable to meet
with accident, and the driving wheel being near the lower end of the
axis, is at the most rigid part, viz., the foundation of the
instrument. As it has a long and very firm polar axis, and is
connected with the foundation plate, it secures the utmost
steadiness and freedom from strain.

An equatorial mounting, with two long and stiff shafts for the axes,
has always the advantage of firmness; the _holding_ portions of the
instrument being in masses, are not liable to receive injury from
blows, and thus be put radically out of order. _No means should be
resorted to to make an equatorial of light weight_; an instrument
cannot be light and slim and at the same time _firm_ and _steady_—no
amount of steadying rods, splines or strings, will make a slender
tripod for a refractor so steady as a firmly made one, with proper
size and weight in the parts.

Another important advantage of this kind of mount for a large size
is, that although it has considerable weight, it is very convenient
to move and set up, being built of convenient parts, which are easy
of separation and removal. The uprights or standards are separate,
and are bolted to the bed-plate, the upper and lower discs are
readily detached from the stand. The cradle and tube are in this
construction separable. The tube of the telescope being suspended
over the _side_ of the stand, is in the most convenient position for
observing objects at any altitude, as the stand is out of the way
and clear of the telescope. The various disadvantages and objections
to the driving clock being _carried_ by the telescope are here
avoided. The clock, which is large and very powerful, is bolted down
to the iron bed-plate, and the telescope, not having to carry the
clock or weight, the balance is never altered nor the rate of the
clock disturbed, and thus a strong clock, keeping regular time, and
working much longer can be used. They will drive 2-1/2 hours. It
will be readily understood that a driving clock to enable the
instrument to do the most exact and best work must be powerful and a
good time-keeper. Lord Lindsay has said that “the clock should have
twice as much power as is _used_,” otherwise the spindles, &c. are
pent up, and it is moreover sensible to any extra weight or work
being put upon the instrument.

To give an idea of the efficiency and regularity of this clock, I
may mention that a Newtonian telescope of 18 inches aperture,
intended to carry a photographic camera of 112 lbs. weight, needed
no additional provisions to do the extra work, the rate and power
not being affected. There is a mechanism in the clock “for making up
of time” and in setting the hour circle can be used with a joint
handle or hooks as a fine screw-motion, and can be applied whether
the clock is going or not. There is also a provision at the
foundation for throwing the instrument out of the meridian, to
follow the motion of the moon or planets with the clock and “maker
up.” The above mounting is equally suitable for “Cassegrains” and
“Newtonians,” to both of which forms it has been successfully
applied up to 18 inches of aperture. It is well suited for large
telescopes.

Fig. 2 is a mounting on the same principle, but with a shorter polar
axis, and the column is in one casting. It is well suited for
moderate sizes, and the circles, &c. are applied exactly as in Fig.
1, but when a clock is wanted there is no mounting equal to the
former.

The “Educational” is a plain 6-1/2 inch, of 4 to 6 feet focus, and
is made to this pattern, with revolving body and screw-motion for
following. It is made as portable as it can be, and is a steady,
good-working instrument, and much approved of.


      THE UNIVERSAL ALT-AZIMUTH.

      (FIG. 3.)

In this mounting I have seen little or no alteration needful, except
that the tube is now made to balance so that the eye-tube can be
reached for objects in the zenith without the observer having to
elevate himself, and the elevating rod can be clamped without the
lever, the legs of the stand are more curved and have more spread in
them.

This “Alt-Azimuth” stand has met with much approval; and where
portability is of consideration and the observer has to set up and
remove the entire instrument after every night’s work, this, or the
Angle-Block stand, will be found the most convenient, more so than
an equatorial in any form. There is much less weight to remove, and
being in three convenient parts is more readily put together and
separated in the dark. If the stand and trunnions can be left in the
open air a very small covering will serve to protect them, and then
the tube alone has to be removed. The equatorial cannot be too
highly recommended where it can be a fixture and undisturbed, as
when once got into proper adjustments its advantages can then be
realised, but not unless it is a permanent fixture. The circles of a
portable equatorial can only be used for very rough reading, and
consequently the adjustments are never in order, and the readings
are of very limited use indeed.


      THE IMPROVED “ANGLE-BLOCK” STAND.

      (FIG. 4.)

With respect to the tube, it is mounted like the Alt-Azimuth, but
with the plane of the horizontal movement corresponding to the
latitude of the place of observation, and therefore following
objects with one screw movement is in reality a telescope with
equatorial motions. It need not be of heavier construction than the
Alt-Azimuth, and there is not the double weight of counterpoising,
&c. as in the equatorial, and when circles are not desired this will
be the most economical, handiest, and easily managed instrument, as
it partakes of the equatorial form or motions. The telescope tube is
well balanced, and the declination movement is easy and free, and
fitted with a clamp screw, so that when the instrument is turned on
an object that object can then be followed by an endless screw.

It can be made to suit any latitude, and by the addition of foot
screws on a level floor, can be got into suitable adjustments, and
if it has to be removed (for the stand is very little heavier than
an ordinary Alt-Azimuth), “guides” can be provided, so that it can
go very approximately into the exact place again when brought out
for use. They are made, when desired, with a revolving body and fine
screw-motion in declination.


      THE “POPULAR REFLECTOR.”

      WITH ANGLE-BLOCK STAND.—(FIG. 4.)

The speculum is 5-1/4 inch diameter, and carefully figured, and is
recommended as a very useful instrument. The size and power of this
telescope has been adopted as that most likely to meet the means and
requirements of a large number of amateurs. Many prefer to commence
astronomical observations with “_something inexpensive_,” and are
led to begin with the popular and well advertised 3 inch refractor
at £5. These, except in a few chance cases, are sure to prove
disappointing, and are perhaps the cause of their giving up any
further attempts to follow up the subject of astronomy, which may
otherwise be so pleasantly and profitably pursued with a reliable
instrument.

It is well known that a less aperture than 4-1/2 inches is
insufficient to give the observer a satisfactory idea of the varied
and most interesting details of the planets, and the ever-changing
outline and tone of the belts and markings of Jupiter, Saturn, and
Mars. Large apertures bring out _details_ when the smaller ones can
only show a _general outline_. The former also delineates more with
a lower power, providing the focus is of proper length.

The planets and nebulæ cannot be seen to advantage without aperture
and focal length. The field of view is then flat, the object is
properly illuminated, with sharp and crisp definition, and is also
_much_ less subject to annoyance from tremour, through the necessity
for constant adjustments in the fields, &c., as is the case with
small apertures, for the object is magnified more in proportion. A
certain magnifying power is necessary in order that the object may
be sufficiently large to scrutinize; and this, whether the aperture
is large or small, must be from about 150 to about 300 times for the
planets. But 150 on a 3 inch is a high power for the quantity of
light obtained, to say nothing of the separate consideration and
advantage of long focus. Aperture is a quality or function of the
telescope considered separately from light or focus. For instance,
suppose a 5 inch speculum is so thinly silvered that it gives the
exact degree of light as a 2-1/2 inch refractor, the defining and
separating power of the 5 inch aperture would be very superior to
the 2-1/2 inch.

The “Popular Reflector,” with 5-1/4 inch speculum of 5, 5-1/2, to 6
feet focus, will be found very suitable, and if its illuminating
power is not greater than a 4-1/2 inch refractor, its defining and
dividing powers are superior. By choosing the above focal lengths,
according to circumstances, the observer can reach the eye-tube,
while standing erect for objects in the zenith, and it is a great
mistake to suppose that the shorter the tube the more handy it
becomes. These foci will not require a “Barlow” lens to flatten the
field. The “Barlow” is very useful for short foci when the aperture
is considerable, as it improves the imperfect correction for
spherical error, but this is much better corrected in the mirror
itself than by a “Barlow” lens, which cannot be used without more
than one disadvantage. There must, by its insertion, be some loss of
light, which can ill be spared with small instruments, and when used
to obtain magnifying power there is some disturbance of colour, and
this subtracts from the beauty and purity of the definition of a
reflector. There is _nothing_ equal to a good eye-piece to obtain
_power_, and _flatness_ of field by the _curve_ of the speculum.

With the “Popular Reflector” and an outlay of a few shillings on
some popular books, such as the excellent work “Celestial Objects,”
by the Rev. T. W. Webb, and some first-class publications by Mr. R.
A. Proctor, especially his smaller star atlas, &c., the amateur can
compare the work he is then capable of doing with a large and
expensive refractor which might be beyond his reach.


      THE ADJUSTMENTS OF THE EQUATORIAL.

When the inexperienced amateur purchases an equatorial with circles,
he should not be without the third edition of “Chamber’s Handbook of
Descriptive Astronomy,” which, besides being an excellent book in
other respects, is a really practical guide to the use and
application of the Equatorial, and is indispensable to the beginner.
He will there find the fullest details of the adjustments to any
degree of exactness. Besides many other matters he will be
instructed in the use and application of apparatus to the perfect
Equatorial, including all kinds of eye-pieces, micrometers, &c.,
&c., as well as other optical instruments and accessories.

The Equatorials described in this catalogue are provided with every
means of adjustment. The cradle contains powerful screws to set the
line of sight at right angles to the declination axis, and shifting
screws to place the polar axis in the meridian and to the correct
elevation, and with care and a few experiments with the adjustments,
and by observations of some catalogue stars, the various adjustments
will soon be correctly made, and the verniers set accordingly.


      THE CASSEGRAIN.

This is a form of reflecting telescope but little known. This is
rather strange, since it is a very much better principle than the
“Gregorian,” so well known to the old observers. Herschel says it
admits of a theoretically perfect telescope. Compared with the
“Newtonian” it has its advantages and disadvantages. Its principal
advantages are, first, the shortening of the tube, which in large
telescopes is sometimes very important. Secondly, the observer has
not to _ascend_ to the eye-tube, the observations being made at the
lower end, as with a refractor. The “Cassegrain” has a flatter field
of view, owing to the action of the curve of the second reflector
causing the rays to travel twice the distance, and, adding the
element of magnifying power, the eye-pieces need not be composed of
small lenses. The adjustments are perhaps a little more trouble, as
the line of collimation must be carefully attended to, this
requiring only a little more care can soon be accomplished, and then
the definition of a good “Cassegrain” is very pleasing.

Amongst its disadvantages is the necessity for the observer to gaze
upwards as with refractors, which, when the object is at a
considerable altitude, is distressing, this is one of the reasons
why the “Newtonian” is so pleasant to use, on account of the natural
and easy position of the observer. The eye-piece being a fixture, it
is not quite so convenient to use some of the accessories of the
telescope. But there are means to overcome these drawbacks, and so
make the “Cassegrain” even more handy than the “Newtonian.”

I have mounted an 18 inch speculum of 12 feet focus in the
“Cassegrain” form, so that objects at any altitude could be observed
with the greatest possible ease. A plane was fixed near the large
mirror to receive the rays from the convex reflector and to throw
them out to the side, illuminating apparatus were fixed here, and
micrometers, &c. used, as if it were a “Newtonian”; the tube was
thus made shorter, and the flat field of a long focus realised, but
there would be a little loss of light in consequence of an extra
reflection, but this, with a large aperture (and the fact that the
“Cassegrain” gives a little more light than the “Newtonian”) can
better be spared, considering the convenience gained. The observer
is not elevated for any altitudes, and a large telescope is actually
occupying less room than a small one. It can be used with or without
the diagonal.

I have, by request, fitted the “Cassegrain” with means for two
observers to view the same object at the same time. A perforated
plane was arranged to receive a portion of the converging rays and
throw them to the side of the tube into an eye-tube, and the
remainder passing on to the eye-tube at the proper place, two images
are thus formed, and can be magnified at will and viewed
simultaneously. The perforated plate was so arranged that it could
be removed at pleasure.


[ Illustration: FIG. 1. ]


[ Illustration: FIG. 2. ]


[ Illustration: FIG. 3. ]


[ Illustration: FIG. 4. ]


      THE ALT-AZIMUTH STAND.

      Fig. 3.

The Telescope, being balanced on trunnions, can be moved from an
elevation approaching the zenith to an almost horizontal position.
In order that it may be secured anywhere between these extremes,
attached to the upper part of the telescope is an iron rod, which,
sliding through the end of the arm of the stand, can be there
clamped. The telescope will now be clamped in _Altitude_. As the
progression of celestial objects will apparently be very slow,
resource must be had to the smoothness of motion obtained by a
screw. The upper end of the Altitude rod is therefore tapped to
receive a long screw with a large milled head, jointed to the
telescope body; by revolving this head the telescope is raised or
depressed accordingly as the screw is unscrewed, or the reverse. It
is necessary that the screw should be withdrawn some way from the
rod before clamping it, preparatory to following an object which has
passed the meridian, or is setting; as perhaps, just when the
clearest vision is obtained, the observer may be annoyed by the
screw action being suddenly stopped by the milled head coming in
contact with the top of the rod.

When viewing objects near the zenith, and the focus long, the handle
attached to the clamp will be found useful, as it can thereby be
reached without leaving the finder. The handle may be so placed that
a downward push should clamp, and an upward pull release.

The second motion in the Alt-azimuth Stand, namely, _Azimuth_, is
obtained as follows:—The strong iron disc which forms the upper
fitting of the legs has its surface accurately turned. On this
revolves an iron disc, rather less in diameter, to which the
trunnions which support the telescope are attached. The main axis of
this disc passes through the centre of the lower disc, and then
through a hollow bearing tube, a continuation of it. All these
fittings having been most carefully turned and ground together,
great steadiness, combined with facility of horizontal movement, is
ensured. In order that this motion can be communicated as evenly as
possible, resource must be again had to a screw which is thus
applied. Just within the circumference of the lower disc is a narrow
groove, turned to such a depth that the ring which is thus separated
from the main disc is still firmly held to it by the uncut portion.
An iron clamp grooved to this ring holds the nut of a long screw,
the plain end of which is jointed to the upper disc. When this clamp
is fixed to the ring, any motion given to the screw will act on the
upper disc, and cause it to revolve, and thus the whole telescope
will be slowly moved in _Azimuth_. The advantages of this plan are
many, the most important being the rapidity and ease with which the
telescope can be shifted from one object to another, even to those
in contrary directions; all that is necessary being to release the
clamp and turn the telescope to the object required. The clamp being
carried round with the upper disc, can be fixed directly the desired
position is obtained, when the screw is at once in action. Should it
happen, whilst following an object, that the screw becomes exhausted
from the joint and clamp coming together, the clamp should be
released, and the screw turned sufficiently in the reverse way to
bring it into action, the weight on the upper disc keeping the
telescope meanwhile in position. If this operation be rapidly
performed, the whole length of screw can be brought in play before
the object has left the field of view of the finder, and can thus be
easily refound with the higher power of the telescope. Motion is
applied to the screw by means of a Hook’s joint, named thus from its
inventor. This joint being furnished with a long handle, enables the
observer, by means of it, to move the Telescope in _Azimuth_ at any
rate, and without removing his eye from the eye-piece.

It will be seen from the preceding remarks that by means of the
vertical and horizontal screw motions, the telescope, when clamped,
can be moved in any direction with the greatest facility, permitting
a celestial object to be observed with high powers for a
considerable time, and with the greatest pleasure and comfort to the
observer.


[ Illustration: decorative ]



[ Illustration: decorative ]

      ADJUSTMENTS.


These instruments are always sent out in correct adjustment, and
with moderate care during transit, and afterwards, will remain so,
but as the performance of the instrument greatly depends on the
accuracy of the adjustments the following instructions will enable
the observer not only to ascertain whether they are perfect, but
also to render them so if found defective. These adjustments are by
no means difficult, and will be easily understood by attention to
the following remarks:—

Into the draw tube screw the “adjusting piece,” which is a small
brass circle with a hole in its centre about 1/20 of an inch in
diameter. (The draw tube should be in about the same position as
when at focus with an eyepiece.) Place the large mirror in its cell
in the tube or body of the telescope, taking care that the three
bayonet-joint pins are correctly placed, that is, with grooves
pointing downward. They will be found to drop easily into their
corresponding holes; care must however be taken that the grooves
have gone well home. Both the speculum and small mirror, or “flat,”
must be uncovered. On looking through the aperture of the adjusting
piece, if the mirrors are in correct adjustment their reflections
will be seen as follows:—the small oval mirror being placed at an
angle of 45° will appear circular, and reflected exactly in the
centre of this circle will be seen the bright image of the large
mirror with a dark round spot in its centre, as shown by Fig. 1.
This dark spot is the double reflection of the “flat,” and should be
concentric with both the bright reflection of the large mirror and
the circular outline of the “flat.” All these should also be
perfectly concentric with the circle given by the stop in the draw
tube. Should these circles not be all central the adjustments are
not perfect and must be rectified as follows.


      To adjust the “Flat” or small diagonal Mirror.

If the bright reflection of the large mirror is seen as a perfect
circle, but not exactly in the centre of the “flat,” the latter
requires adjustment; for this purpose loosen the milled head screw
at the middle of the back of the “flat” which in large instruments
is made sufficiently heavy to act as a counterpoise to prevent
vibration. This will allow the “flat” to be rotated by the hand
vertically with respect to the tube of the telescope. Bring the
bright circular reflection of the mirror exactly central in this
direction, and fasten in position by screwing up the milled head
screw or counterpoise. If the circular reflection is quite central
no further adjustment is required, but if not, then, after
completing the vertical adjustment, as described, proceed to make
the horizontal adjustment by turning in one or other direction the
milled head of the horizontal adjustment screw, situated in front of
the vertical adjustment screw; this will bring the circle of light
exactly into its proper horizontal and central position, and the
adjustments are then completed.

If the bright reflection of the large mirror is _not_ seen as a
perfect circle, and the small dark spot not in the centre, the
speculum is out of adjustment, and consequently the adjustment of
the “flat” is best performed by removing the large mirror or
speculum with its cell and so arranging the body of the telescope
that on looking through the “adjusting piece” a large sheet of white
paper spread on the ground a short distance from the open end
appears as a white circle of light reflected in the “flat.” Now
bring this white circle exactly into the centre of the flat
precisely in the way described above, and on this being accomplished
replace the speculum uncovered with its cell, and proceed.


      To adjust the large Mirror or Speculum.

[ Illustration: Fig. 1. Fig. 2. Fig. 3. Fig. 4.]


When in perfect adjustment the large mirror viewed through the
“adjusting piece” should appear as before stated, as a complete
bright circle, with the image of the “flat” as a smaller dark
circular spot exactly in the centre (Fig. 1). Should this not be the
case it must be rectified by means of the three adjusting screws at
the back of the cell. Proceed as follows:—First unloose (by a few
turns) the small clamping screws which pass through the larger
hollow adjusting ones; then, on looking through the adjusting piece
the relative position of the image of the “flat” should be carefully
noted. If the dark spot is nearer the bottom, and consequently more
of the top part of the bright circle is seen (Fig. 2), the mirror
reflects too much of the upper part of the tube, and therefore the
top of the mirror leans too far back and must be pushed more forward
by screwing in the top adjusting screw (_a_ Fig. 1) a little at a
time till the dark spot is central. Should the spot be towards the
top (Fig. 2 _inverted_), the reverse holds good and the top
adjusting screw (_a_) must be _un_screwed or the two other adjusting
screws turned in. Should the spot be towards the left (Fig. 3),
screw up the right adjusting screw (_c_ Fig. 1). If towards the
right (Fig. 4), screw up the left adjusting screw (_b_ Fig. 1). The
dark spot is always furthest away from that part of the tube which
is too much reflected, and from the adjusting screw that must be
turned in to correct it.

When all the adjustments are considered perfect, as in Fig. 1, the
small screws are to be clamped up to keep the adjusting screws in
position. If, after the greatest care has been taken in adjustment,
a flare should appear on looking at a star (say of the second
magnitude) with an eye-piece of a high power, and the diffraction
rings are not quite concentric, it can generally be rectified by
turning the large screws of the mirror round in cell a little at a
time. If this does not remove the flare the adjustment of the
“flat”. is not sufficiently correct and must be altered by means of
the screws at its back. If the flare is at the top or bottom of the
star the “flat” must be very slightly revolved by the hand, after
unloosing the middle screw, and when correct reclamping it. If at
either side, namely, in the direction of the major axis of the
“flat” and in a line with the tube, the “flat” must be altered by
the long screw. It is always advisable to leave the telescope for a
short time undisturbed, especially if, on first looking at a star, a
flare should appear, as these appendages often vanish when the
instrument has been for a short time in the air. These adjustments
may at first appear somewhat difficult, but are rendered remarkably
easy by observing how the different screw movements alter the
positions of the reflections. A useful test as to the correctness of
the adjustments may be obtained by viewing a star with a high power
eye-piece out of focus. When in the centre of the field it should
appear as a bright luminous circle with a circular dark spot in the
centre, the size of the bright circle diminishing as the focus is
approached and the dark spot remaining central.

The cell mount of the large mirror can be removed from the tube and
replaced without disturbing its adjustments, but it is very
advantageous if the entire instrument can always be left undisturbed
when not in use in an observatory of light construction, having a
skeleton revolving dome, covered with well oiled canvas or calico,
and made with a wide opening and large shutters. The Rev. E. L.
Berthon has described in the “English Mechanic,” October 13th, 1871,
an observatory of this kind most admirably suited to shelter a
reflector, as the temperature inside would be as nearly as possible
that of the external air, and no annoyance from damp would be
experienced. Where an observatory is not practicable the telescope
might be protected by a close fitting covering of like make. Both
the large and small mirrors should be protected by their covers
(with which they are provided), when not in use, especially if left
in the open air. The larger sized tubes have a door large enough to
admit the cover and so allow of its being put on the large mirror
without the necessity of the speculum being removed from the body of
the telescope.


      To Adjust the “Finder.”

Direct the telescope to any bright star (the Pole-star being by far
the best, as it has very little apparent motion), and bring this
star into the centre of the field of a low-power eye-piece. Now
adjust the “finder” by means of the three screws bearing on it, till
the star is bisected by the cross wires seen in the focus of the
eye-lens of the “finder.” Change the low eye-piece to a high one,
and perfect the adjustment as before described. Any well-defined
terrestrial object at a distance can be employed in the day-time to
roughly adjust the “finder,” leaving the final adjustments to be
made by a star.


      The use of Stops.

A stop 1/4 inch less in diameter than the speculum, is often useful,
in order to cut off the internal reflections of the tube.

With mirrors 6-1/2 inches in diameter and under stops are seldom
required; with the 6-1/2 inch a 5 inch stop may however sometimes be
used with advantage on very bright objects. With an 8-1/2 inch
mirror a 7 inch stop often improves planetary definition.

With larger sizes than 8-1/2 inches several stops of different
diameter may be used, when experiment will determine what size is
best suited to the condition of the atmosphere, and the character
and brilliancy of the object to be observed. These stops can be
easily cut out of thin cardboard and afterwards blacked with
Indian-ink or lampblack.


      On Observing the Sun.

No larger aperture than 4-1/2 inches should be employed for solar
observation, except with a specially constructed “Solar Eye-piece,”
as even a 4-1/2 inch speculum often concentrates sufficient heat to
crack the coloured glass of an ordinary sun-cap, if exposed for any
length of time.

If a “solar eye-piece” is employed, the whole aperture may be used.
In viewing the moon a slightly tinted glass is often most useful,
especially to persons with weak sight, as it takes off a great deal
of the glare.


      TO SILVER AND POLISH THE SPECULA.

The cost of silvering is trifling, and with cleanliness and ordinary
care very little difficulty will be experienced. The apparatus and
chemicals required consist of the following articles:—

APPARATUS.—A Silvering Vessel:—This should be a flat-bottomed
circular glass or glazed dish, 1 inch or more larger in diameter than
the speculum to be silvered, and sufficiently deep to allow of a stratum
of fluid of an inch or rather more between the face of the mirror and
the bottom of the dish, the top of the mirror being nearly level with
the edge of the dish.

A Mixing Vessel:—A 40 oz. glass measure will answer well, but care
should be taken not to scratch the sides whilst stirring, or the
glass is liable to fly. Should a measure not be procurable, any
receptacle of sufficient size may be used, but a glass one is best,
as it will allow of the action of ammonia being better observed.

      A Box of Scales and Weights.
      A Glass funnel and filtering paper.
      Two Glass Rods for Stirring purposes.
      A Five-ounce Glass Measure.
      A Test tube 3/4 or 1 inch in diameter.
      Some Clean Cotton Wool.
      Some very fine Wash-leather.
      A Support of Wood, on which to cement the speculum, described
        further on.

All these articles should be perfectly clean and free from dust, and
the Glass ones well rinsed with distilled water just before using.

  CHEMICALS.—Nitrate Silver.
      Potash pure, precipitated by Alcohol.
      Sugar of milk powdered.
      Nitric Acid, pure.
      Liquor Ammoniæ.
      Distilled water, pure.
      Pitch.
      Fine Rouge.
      Turpentine.

Procure a strip of wood an inch or so less in diameter than the
mirror, and of sufficient length to rest securely on the opposite
sides of the silvering vessel. Pour on this piece of wood some
melted pitch, and whilst it is still hot, place on it the back of
the speculum moistened with a little turpentine; when cold, reverse,
and lay the cemented speculum face downwards, suspended in the dish.
Should the distance between the face of the mirror and the bottom of
the dish be less than an inch, raise the mirror by means of thin
wedges, placed between the strip of wood and the edges of the dish.
But if, on the contrary, the mirror should be considerably more than
an inch away from the bottom, which will occur if the silvering
vessel is very deep, the speculum must be cemented to a block of
wood of sufficient height, screwed to the suspending strip, instead
of being cemented directly to the strip itself.

When the speculum is properly placed in the dish, namely, with the
front surface about one inch from the bottom, pour in water till the
fluid reaches about 1/4 inch up the side of the mirror. Measure this
quantity, as it will indicate the total amount of the silvering
solution required to be prepared.

To prepare the Silvering Solutions—make 3 standard solutions as
follows—

  No. 1. {Nitrate Silver in crystals  100 grains.
         {Distilled water               4 oz.

  No. 2. {Potash pure by alcohol        1 oz.
         {Distilled water              25 oz.

  No. 3. {Powdered sugar of milk      1/2 oz.
         {Distilled water               4 oz.


Solution No. 3 must be made just before using. The others will keep
if the distilled water employed in their preparation is pure, and
the solutions, when made, are kept in glass stoppered bottles.

Suppose it is desired to silver an 8-1/2 inch mirror, proceed as
follows:—the total amount of solution required having been
ascertained, as before described, pour 2 ozs. of solution No. 1 into
the mixing vessel previously well washed and rinsed with distilled
water, and cautiously add Liquor Ammoniæ. A grey precipitate will be
formed; continue to add the ammonia, drop by drop, till the
precipitate is just dissolved and the solution becomes clear. The
solution should be well stirred with a glass rod whilst adding the
ammonia. Now add 4 oz. of solution No. 2, and re-dissolve the brown
precipitate which is produced with Liquor Ammoniæ as before
described. There will now be about 6-1/2 oz. of solution. Subtract
the 6-1/2 oz. from the total amount previously ascertained to be
required, and the remainder will be the amount of distilled water to
be added. Add half this quantity of distilled water to the 6-1/2 oz.
of solution, and add a drop at a time of solution No. 1, till there
is a slight precipitate, which cannot be re-dissolved by a
considerable amount of stirring (say for 2 or 3 minutes); then add
the remaining half of distilled water and cover up from dust the
vessel containing the solution, so as to allow the slight
precipitate to settle. There is a point of importance to be attended
to, namely, that no more ammonia is employed than is absolutely
necessary. The total amount of ammonia required in the 6-1/2 oz. of
solution is about 2 drs.


      To Clean the Mirror.

Fill the end of a test tube with cotton wool, leaving plenty outside
the tube. Having poured a small quantity of strong nitric acid on
the front of the mirror, rub the acid well all over the front and
sides with the cotton wool brush. Place the speculum under a water
tap for a few minutes till the acid is washed away, and finally well
rinse with distilled water; then place it in the silvering vessel
(previously thoroughly cleansed) and pour in distilled water till it
reaches 1/8 inch up the side of the speculum.


      To Mix the Solutions.

The precipitate having settled, pour into a clean vessel all that is
clear of the solution, leaving about 2 oz. behind, which will be
turbid with the precipitate, and therefore useless. The total amount
will be afterwards made correct by the addition of the same quantity
of solution No. 3. Having filtered solution No. 3, warm it to about
100° F. by allowing the bottle to stand in warm water, or by heating
in a small flask. When everything is quite ready, add 2 oz. of the
filtered solution No. 3, whilst warm, to the clear solution
described above, and thoroughly mix.


      To immerse the Mirror.

Remove the mirror from the distilled water, taking care not to touch
the surface of the mirror, and wipe the back and edge with some
clean cotton wool. If this precaution is not taken the water is
liable to drain down the sides of the mirror whilst silvering, and
cause streaks at the edge of the film. Having poured away the
distilled water in the silvering vessel, substitute the mixed
solutions, and directly the solution becomes slightly inky, gently
immerse the mirror, taking care that no air bubbles, or specks of
any kind, remain between the surface of the mirror and the solution.
The mirror should not be removed from the bath until all the silver
has been exhausted from the solution. This may be known by the
solution being clear below the silver film on the surface of the
liquid. The time required will vary from 45 minutes on a hot
summer’s day, to 90 minutes when the thermometer shows a low degree
of temperature. In the latter case it is better to have the
silvering bath in a warm room.

Immediately the mirror is removed from the bath, the silvered
surface should be well washed by allowing ordinary water to flow on
it from a tap, for five minutes or more, then finally rinse with
distilled water and place the mirror to dry with the silvered
surface resting on some blotting paper. It is as well if the mirror
can be left undisturbed for a day or two, as the film will be
firmer, but it may be polished, if desired, after drying for a few
hours.


      To Polish the Silvered Surface.

Make a couple of polishing pads by filling two pieces of very soft
wash-leather about six inches square loosely with cotton wool, and
tie them into balls. Gently remove any dust that may have settled on
the film with some loose cotton wool, and then go over it with one
of the pads in small circular strokes for about 15 minutes. This
will consolidate the film and fit it for polishing. Spread a little
of the finest rouge on a sheet of writing paper, and impregnate the
other pad with it. Go over the film with the rouged rubber with the
same circular strokes till it is perfectly polished, which will take
another 15 minutes or so. Never commence with the rouged pad, as the
surface may be injured. When once the film has been consolidated it
will remain so, and can be repolished many times with the rouged pad
should it get tarnished. The pads should be kept from dust in
wide-mouthed bottles for future use. With care the film will last
for a long time, especially if it is not allowed to get damp, and
consequently the mirrors should never be brought uncovered from the
cold air to a warmer temperature.

The “flat” may be silvered and polished in the same way as the
speculum, using a smaller appropriate vessel for the silvering
solution.


      To Separate the mirror from the Wooden Support.

Should the mirror be attached directly to its support, insert a
chisel between them, when one or two gentle blows will cause them to
separate, but, should the mirror be cemented to a block, stand the
mirror on edge, when a slight tap on the block will detach it.
Scrape off any pitch that remains on the back of the mirror, using
finally some turpentine to wipe it clean. Great care should be taken
not to finger the film.


      Martin’s process for Silvering.

Prepare four solutions of any quantity. Keep in stoppered bottles.

_Solution 1._—Dissolve 175 grains of pure nitrate of silver in 10
oz. of distilled water.

_Solution 2._—Dissolve 262 grains of pure nitrate of ammonia in 10
oz. of distilled water.

_Solution 3._—Dissolve 1 oz. avoirdupois of pure caustic potash
(prepared by alcohol) in 10 oz. of pure distilled water.

_Solution 4._—Dissolve 1/2 oz. avoirdupois of pure sugar candy in 5
oz. of distilled water, then add 32 grains of tartaric acid and boil
in a flask or other clean glazed vessel for 10 minutes, when cool
add 1 oz. of alcohol and then dilute with distilled water, so as to
make up the volume to 10 oz.

For silvering use equal parts of each, mix solutions 1 and 2
together, and 3 and 4; when the mirror is ready mix the whole
together in the silvering vessel and quickly suspend the mirror.

In the summer time, if the solution cannot be kept in a very cool
place, the mirror must be quite ready to be placed in the bath, as
the solutions turn instantly when mixed together.


[ Illustration: decorative ]



      SELECTED TESTIMONIALS


                              11, WELLINGTON PARK TERRACE, BELFAST,
                                        _July 7th, 1876_.

DEAR SIR,—The night before last was a clear night and I got the
6-1/2 inch out, and though the air was not good when using a 3-1/4
inch refractor, I was much pleased with the performance of the
mirror.

Mr. W. came up about 11 o’clock and stayed till one, we got it on
Saturn, and although rather low it was really a fine sight, Mr. W.
was much pleased.

The moon being near to full we could not do much with faint points
of light.

                                  Yours sincerely, W. E. PARKINSON.

Mr. G. CALVER.

       *       *       *       *       *

                                        74, HAGLEY ROAD, EDGBASTON,
                                             _November 27th, 1876_.

DEAR SIR,—I have now got the 5-inch speculum fairly into adjustment,
and I am well pleased with it. Last night, the sky being clear for a
short time, I turned it on the moon, the definition of minute
craters was all that could be desired. I hope to have better
opportunities.

                                        I am, Yours truly, F. G. L.

Mr. G. CALVER.

       *       *       *       *       *

                                        74, HAGLEY ROAD, EDGBASTON,
                                             _November 21st, 1876_.

DEAR SIR,—I have mounted the 5-inch speculum on a simple equatorial
and it works well. I am sure it will turn out a fine glass and I
shall not regret the time and pains I have spent over it. It is not
quite in adjustment yet, when it is it will afford me a treat. I
have just tried it once on the Orion Nebula and Trapezium, details
of Nebula well seen, and the 5th star in Trapezium easy.

                                        I am, Yours truly, F. G. L.

       *       *       *       *       *

                                                 DOWLAIS,
                                             _December 27th, 1876_.

DEAR SIR,—I have thoroughly tested the speculum, and am pleased to
tell you it stood its trials well.

                                              Yours truly, D. C. C.

Mr. G. CALVER.

       *       *       *       *       *

                                           ST. DENIES, SOUTHAMPTON,
                                               _August 14th, 1876_.

DEAR SIR,—With reference to your enquiry as to the performance of
the 6-1/2 in. reflector. I have pleasure in stating that I am
perfectly satisfied. It readily divides the test objects and shows
delta Cygni with as low a power as 160. The comes to Sirius may be
considered an atmospheric test, perhaps, but I have repeatedly seen
it. Your stand I find very steady and convenient; altogether I can
fairly say that I consider that I have an instrument of considerable
power at a comparatively small cost. I now find the attempt to
observe with a refractor the reverse of pleasant.

The owner of a 3-inch refractor, after using my reflector, writes
that he envies me its power, ease, definition, and comfort in
observing.

                              I am, Dear Sir, Yours truly, A. H. S.


       *       *       *       *       *

                                         HILGAY RECTORY,
                                             _February 20th, 1877_.

DEAR MR. CALVER,—The sky last night cleared up in places and enabled
me to try the 10-inch; there was a slight haze, but I never saw
discs so perfect and neat. I felt certain it would divide anything
divisible. Clouds came up and put an end to work.

                         I am, Dear Sir, Yours sincerely, St. V. B.

       *       *       *       *       *

                             25, HAMILTON TERRACE, ST. JOHN’S WOOD,
                                        _May 26th, 1877_.

MY DEAR SIR,—I have much pleasure in informing you that the very
first time I saw Saturn through your 6-1/2-inch reflector, the
definition of the planet was far superior to anything I had observed
before, even with a good 4-1/4-inch refractor; and on another
occasion I was greatly pleased with the clear and easy view of the
“Comes” to ε Boötis. But even without including the stars, the views
of Saturn and Jupiter through my 6-1/2-inch mirror do _alone_ (in my
opinion) well repay the cost of the telescope.

                                     Yours truly, WM. L. LANCASTER.

Mr. G. CALVER.

       *       *       *       *       *

                                            37, EATON RISE, EALING,
                                             _February 13th, 1877_.

DEAR SIR,—I like the 18-inch speculum, and I think it as good as it
can be, and if the larger one is as good I shall be delighted with
it. It gives beautiful star images: I see Sirius as a brilliant dot,
a glorious object without ray or flares of any kind. I never saw it
so well before.

                                              Yours truly, A. A. C.

Mr. G. CALVER.

       *       *       *       *       *

                                            37, EATON RISE, EALING,
                                              _February 3rd, 1877_.

DEAR SIR,—I have tried the 18-inch speculum on some tests, and
especially the satellites of Uranus, and it appears fine, very fine.
What I have done in photography promises well.

                                              Yours truly, A. A. C.

Mr. G. CALVER.

       *       *       *       *       *

                                           SOUTHEND ON SEA,
                                                _March 17th, 1877_.

MY DEAR SIR,—Circumstances have prevented me from making many
observations of late, but I am more confirmed in my opinion that my
telescope of your make is a very fine instrument. (A 6-1/2-inch.) I
heartily wish you success, which I feel sure you will obtain, as you
are so painstaking and turn out a thoroughly reliable article. I
shall be curious to compare my brother’s telescope with mine.

                                          Sincerely yours, J. L. L.

Mr. G. CALVER.

       *       *       *       *       *

                                           GORLESTONE,
                                                _March 30th, 1875_.

DEAR SIR,—You have asked me for my opinion of the 10-inch speculum.
I have tested it, and can speak in the highest terms of its
performance. Definition in good air is as near perfection as it is
possible to imagine. Such tests as ζ Cancri, γ^2 Andromedæ are well
divided. The 6th star in the trapezium stands out well clear of its
brighter neighbour. On the moon any power may be applied, only
lessening the light, but retaining sharpness of outline. I have
tried a good many telescopes, but never yet saw these 10-inch
mirrors surpassed. The image of a star disc expanded on each side of
the focus is of as nearly the same appearance as possible.

                                       Yours truly, W. P. MATTHEWS.

       *       *       *       *       *

                                           416, BRIXTON ROAD,
                                                _April 20th, 1875_.

DEAR SIR,—In compliance with your request, I send particulars of my
observation on φ Draconis. It was about 12.45 this morning when I
directed my 8-1/2-inch to this object, the air was very unsteady, in
fact not nearly so good as some nights lately, and I well divided it
with a power of 450. I then used a 6-1/2-inch stop, which I found
very much increased the steadiness of definition.

                                     Yours very respectfully, P. H.

       *       *       *       *       *

                                                 _10th July, 1874_.

DEAR SIR,—I tried the 6-1/4-inch mirror I had from you for the first
time last night. The night was not a good one for definition, but I
was very much pleased indeed with its performance.

                                              Yours truly, C. H. W.


       *       *       *       *       *

                                             HONITON RECTORY,
                                                 _Dec. 23rd, 1874_.

DEAR SIR,—I have been wishing to tell you how pleased I am at the
performance of your mirror. Many thanks for your kind offer to
change the mirror if needful, but I think it could hardly be better
than it is, its performance on different double stars is most
excellent. I have examined nearly 100 of these since September with
the 6-1/2-inch, most of them very difficult, but the mirror came out
well under all tests. I send you a list of some of the objects I
have examined.

                                            Yours truly, H. SADLER.


π _Aquilæ._—Divided, power 80. 14-^m. Webb might have been rated
15-^m. [6-^m., 7-^m. 1″·5.]

             A      B   C   A-B  A-C
δ _Aquilæ._—[3-1/2, 16, 14, 96″, 194″.] Comites easy, 3 other
excessively minute ones, not shown by the 11-in. refractor with
which P. Smyth measured B.C. Found 6-1/2-in. Sept. 12th, est. ± 17
mag. 100″ to 110″.

ζ _Persei._—My friend “Linea” sees two minute stars with 4·28-in.
Wray, not in Webb, and Wray himself sees an excessively difficult
companion. I see these 3 stars easily with 6-1/2-in. (Wray says his
companion is “very difficult with 7-in. refractor, really only a
glimpse star, even with the best atmosphere”), and have added two
more stars to the group.

β _Delphini._—Close double discovered by Burnham, est. 0″·7. In
contact 6-1/2-in., power 430.

η _Coronæ Borealis._—Very low, long past meridian, in contact 164
power.

              _a_    _b_  _c_  B   _a-b_  _a-c_  _b_-B
β _Equalei._—[5-1/2, 13,  14,  16: 35″,   50″,   3″.] 16-^m. not
seen, Webb 9-1/3-in. Just divided 164, easy 430 power. Two other
companions (not seen by Smyth or Webb?)

μ _Andromedæ._—The 16-^m. comes, a very difficult test, easy; other
comites (not seen by Smyth or Webb?) seen.

Companion to Vega pretty easy, Nov. 12th, 37m. after sunset.

                          _a_    b  _c_  B   _a-b_   _b_-B  _a-c_
_P._ 178 xx. _Delphini._—[7-1/2, 8, 16,  9:  14″·3,  0″·7,  20″.]
Smyth 16 by evanescent glimpses; easy 164 power, 6-1/2-in. 8-^m.
well elongated in direction of 230°, power 430.


       *       *       *       *       *

                                       REGENT ROAD, GREAT YARMOUTH,
                                           _October 24th, 1874_.

DEAR SIR,—Doubtless you have anticipated hearing from me, relative
to the 10-inch telescope, but the weather has been so indifferent
for delicate astronomical work that it has not yet had a fair trial.

In middling good air, when I could use a reduced aperture with
satisfactory results, the star images reminded me of the 6-1/2-inch,
which I considered so superb a mirror that nothing could surpass its
fine performance either on stars or planets.

With the recollections of the truly splendid views I had of Jupiter
last season, I count much to see him with the 10-in.

                                             Yours truly, H. BLYTH.

       *       *       *       *       *

                                       REGENT ROAD, GREAT YARMOUTH.
                                           _February 2nd, 1875_.

DEAR SIR,—In reply to yours, I have not had a really good night to
test severely the defining powers of the 10-inch mirror, but judging
from the few difficult objects I have seen, the mirror promises
well, and I have no doubt of its excellence.

I had a fine view of the grand nebula in Orionis, and noticed that
the 5th and 6th stars were quite plainly seen, when the aperture was
reduced to 5-1/2-inches. I consider your stand a great improvement,
being very convenient and steady.

                                             Yours truly, T. AYERS.


[ Illustration: decorative ]



      CATALOGUE

      OF

      Silvered Glass Reflecting Telescopes, &c.,

      AND THEIR ACCESSORIES,

      JUNE, 1877.


G. Calver, while introducing the list of prices below, has the
greatest confidence in calling the attention of the practical
astronomer and the amateur to the very moderate prices charged,
considering the principle and style of the mounting, and the firm
and well-fitted arrangements in all the parts.

The principle of the mounting is that which is the most convenient
to use, and with the greatest degree of steadiness with the easiest
movements. Fig. 1 is the _best mounting ever applied to the
Reflecting Telescope_.

He is also able to state, that with his processes and special
facilities for working large specula, and substantially mounting
them, he is prepared to construct automatic equatorials of large
sizes, and with any special arrangements that may be required.


SILVERED GLASS EQUATORIAL TELESCOPES, very substantially and
well-fitted, as (Fig. 2). All these equatorials have revolving body.

                                                              £  s. d.
  5-1/4 inch Speculum from 4 to 6 feet focus, with 8 inch
     hour circles reading to 5 seconds of time, and
     declination circle reading to 1 minute, two powers      30  0  0

  6-1/2 inch Speculum of from 5 to 6-1/2 feet focus,
     10 inch rotating hour circle, reading to 5 seconds of
     time, and declination circle to 1 minute of arc, with
     3 powers--100 to 500                                    45  0  0

  8-1/2 inch Speculum as above with 12 inch circles,
     4 powers                                                70  0  0

  9-1/4 inch Speculum as above with 12 inch circles,
     5 powers                                                78  0  0

  10 inch Speculum as above with 12 inch circles,
     5 powers                                                90  0  0

  12-1/2 inch Speculum as above with 12 inch circles,
     5 powers                                               120  0  0


Any of the above sizes mounted on Stand (Fig. 1), from 5 per cent.
extra.

Fig. 1 is a very excellent stand, and admirably suited for large
instruments with clock power, and is convenient to remove and adapt
to different latitudes, &c., see p. 20.

                                                              £  s. d.
  14, 15, to 16 inch Speculum mounted as (Fig. 1), with
      rotating hour circle reading to 5 seconds and
      declination to 1 minute (the diameter of the circles
      never less than that of the Speculum and often larger)

  8 powers from 50 to 700, with first-rate and very
      powerful driving clock, first-class instrument,
      and complete                           from £220 to   330  0  0

  17, 18, to 20 inch Speculum, with 10 powers,
     from 50 to 800, including Kellners, Huyghenians,
     and Achromatics,                        from £350 to   500  0  0

  22 to 24 inch Speculum                     from £550 to   750  0  0

  30 inch Speculum, with 12 powers and position
     micrometer, and transit eye-pieces                    1000  0  0

Prices will be forwarded for special arrangements in any of these
large sizes.


The CASSEGRAIN TELESCOPE is a very convenient form, and perfect in
performance, and in this form a very large instrument requires
comparatively a much smaller observatory, and is more conveniently
worked. They can be made so that the image is thrown out at the side
and viewed diagonally, as with the Newtonian, see p. 35. Cassegrains
from 5 per cent. extra.

                                          £  s. d.
  Driving Clocks for 6 to 10 inch        35  0  0
       〃      〃   12  〃 18   〃         40  0  0
       〃      〃   20  〃 30   〃         50  0  0


The EDUCATIONAL REFLECTOR is a plain and very steady and
satisfactory instrument, mounted on (Fig. 2) stand, without circles,
has revolving body, and made so as to be portable.

                                                              £  s. d.
  6-1/2 inch Speculum (clear aperture), and of 4 to
     6-1/2 feet focus, has screw-motion in right ascension,
     2 powers                                                25  0  0

  8-1/2 inch speculum as above, with 3 powers                40  0  0

Any of these equatorials can be, according to wish, fitted without
the circles, &c., and dispensing with that which is not needed, so
as to reduce the price to suit circumstances and convenience.


The POPULAR REFLECTOR, with Angle-Block Stand, with endless
screw-motion to follow the stars with equatorial motion.

                                                             £  s. d.
  5-1/4 inch Speculum, of from 4 to 6 feet focus,
      with 2 powers                                         15 15  0


      (See p. 20, Fig. 4).


Reflecting Telescope on Alt-azimuth Stand, as described at page 13,
fitted with Silvered Glass Speculum, and provided with Two
Eye-pieces.

                                                     £  s. d.
   5-1/4 inch Speculum, 4 to 6     feet focus       19 10  0
   6-1/2   〃      〃    4 〃 6-1/2     〃            24  0  0
   8-1/2   〃      〃      〃 6-1/2     〃            33 10  0
  10       〃      〃      〃 7         〃            45  0  0
  12-1/2   〃      〃      〃 8         〃            70 10  0


Reflecting Telescope on Cradle Stand, and provided with Two
Eye-pieces.

                                                      £  s. d.
   5-1/4 inch Speculum, 4 to 6 feet focus            21  0  0
   6-1/2   〃      〃    4 〃 6-1/2 or 5 feet focus   27  0  0
   8-1/2   〃      〃      〃 6-1/2       〃     〃    36  0  0
  10       〃      〃      〃 7           〃     〃    49  0  0
  12-1/2   〃      〃      〃 8           〃     〃    76  0  0


      SILVERED-GLASS SPECULA (_unmounted_).

      THE FINEST QUALITY GUARANTEED.

                                                     £  s. d.
   5-1/4 inch diameter  4 to  6 feet focus           5  0  0
   6-1/2         〃     4  〃  6-1/2  〃              6  5  0
   8-1/2         〃        〃  6-1/2  〃             13  0  0
  10             〃        〃  7      〃             25  0  0
  12-1/2         〃        〃  8      〃             38 10  0
  14             〃        〃  8      〃             55  0  0
  16             〃        〃 10      〃             75  0  0
  18             〃        〃 12      〃            100  0  0
  20             〃        〃 12      〃            130  0  0
  22             〃        〃 15      〃            165  0  0
  24             〃        〃 18      〃            200  0  0
  26             〃        〃         〃            250  0  0
  30             〃        〃         〃            300  0  0
  36             〃        〃         〃            400  0  0


      SILVERED-GLASS DIAGONAL MIRRORS (_unmounted_).

      FINEST QUALITY GUARANTEED.

                                                                £  s. d.
 1 inch in the minor axis, or narrowest diameter of the ellipse 1  0  0
 1-1/2         ditto            ditto            ditto          1 10  0
 2             ditto            ditto            ditto          2  0  0
 2-1/2         ditto            ditto            ditto          2 10  0
 3             ditto            ditto            ditto          3  3  0
 3-1/2         ditto            ditto            ditto          4  4  0
 4             ditto            ditto            ditto          5  5  0


      SILVERING AND POLISHING SPECULA.

                               £   s.  d.
   5     inch                  0   6   0
   6-1/2   〃                  0   8   0
   8-1/2   〃                  0  10   6
  10       〃                  0  15   0
  12-1/2   〃                  1   1   0
  Diagonal Planes      3s. to  0   5   0


      ASTRONOMICAL EYE-PIECES.

      OF BEST QUALITY.

Huyghenian Construction of the following magnifying powers on a 6-1/2
feet focus object-glass:—

                                       £   s.  d.
  35, 60, 90, 130, 180, 200      each  0  15   0
  320, 450                             1   1   0
  610                                  1   7   6

      All fitted with Sunshades.


      Improved Achromatic, Ramsden’s Construction.

                                       £   s.  d.
  90, 130                        each  1   0   0
  189, 250                             1  10   0
  320, 450                             1  12   6
  610, 750                             1  15   0
  850                                  2   2   0


      Kellner’s Construction.

                                        £   s.  d.
  30, 58, and 80                  each  1   5   0


      SOLAR EYE-PIECES.

                                                            £   s.  d.
  Solar Diagonal, with true plane                           1  12   6
  Dawes’ Solar Eye-piece                                    8   0   0
  Barlow’s Lens                                             1   1   0
  Day Erecting Eye-piece                                    1   5   0
  Coloured Eye-piece Cap for observing the Moon             0   4   0
  Transit Eye-pieces, for use with Equatorials   £1 1s. to  2   2   0
  Adjusting Piece                                           0   2   6


      MICROMETERS.

                                             £   s.  d.
  Parallel Wire Micrometer                   5   5   0
  Position Micrometers           £8 8s. to  15  15   0
  Double Image Micrometer                    8   8   0
  Illuminating Apparatus              from   8   0   0


_Good Instruments will be taken in exchange and liberally allowed
for._


      GEORGE CALVER,

          HILL HOUSE, WIDFORD,

              CHELMSFORD, ESSEX.


[ Illustration: decorative ]



      APPENDIX TO Hints on Silvered Glass Reflecting Telescopes.


The object of this pamphlet is to give some new and additional
advice not contained in my “Hints on Silvered Glass Reflecting
Telescopes,” on silvering and adjusting them; and, as the results of
continued and recent experience, it is hoped they may be useful, and
may prove an acceptable appendix to my little book of Hints.

The first thing to do after fastening the mirror to the wooden
support, is to suspend it in the dish in which it is to be silvered,
and so to adjust it that there shall be one inch between the bottom
of the mirror and the bottom of the dish; then pour in water to come
a quarter of an inch up the sides of the glass—the quantity thus
found is to be measured, and will be the exact amount of the bath
when all the solutions are mixed; this will prevent any hitch at an
important moment, and the glass can be immersed without delay or
disturbance.

Next proceed to wash the surface with nitric acid, taking care that
the acid does not run down the sides, as it is not so easily removed
from the fine ground sides as it is from the polished surface. After
gently but thoroughly rubbing the surface, add a little water, and
again go over; then wash all off, and take a large piece of cotton
wool and well sponge the surface and sides with plenty of water, and
suspend in a dish or plate with water in it.


      TO PREPARE THE SOLUTIONS.

The plan I adopt is this,—I dissolve a large quantity of the
chemicals required in one-fourth or one-eighth the quantity of water
employed by Martin, so that in a Winchester quart stoppered bottle I
can keep a large supply ready. I make the silver and ammonia
solutions eight times the original strength, the potash and sugar
solutions four times only, as these latter solutions require more
water to properly prepare them.

Enough solutions to silver a 6-1/2 in. mirror, eight times are to be
made.

Dissolve 1400 grains of nitrate of silver in 10 ounces of water (it
may be clean fresh rain water filtered, if distilled is difficult to
obtain, and it will act very well), but do not put the silver into
the exact 10 ounces, but make up to exact 10 ounces after the silver
is dissolved. It is thus condensed eight times. Do the same with the
nitrate of ammonia, by dissolving 2096 grains.

Next prepare the potash and sugar solutions, condensed to four times
the initial strength.

Dissolve 8 ounces of potash, and make up to exactly 20 ounces of
water; if this is dissolved in a glass measure it will evolve
sufficient heat to break it; it is safely done in a clean white jug.
Lastly, dissolve 4 ounces of white sugar candy with 416 grains of
tartaric acid, and boil ten minutes in a clean glazed vessel; when
cold, add 8 ounces of alcohol, and make up to 20 ounces with water.

Do not use the solutions till all are of the same temperature, nor
on the same day as they are made; and do not silver until the glass,
and _everything_ used are of the same temperature. To insure this,
get the mirror ready and suspend in water, with the solutions all
collected in the room in which the silvering is to be done, and let
them remain until next day.

Now, remembering how many ounces were needed to leave one inch of
solution under the surface and a quarter of an inch up the sides of
the 6-1/2 in. mirror, using a vessel about 2 inches larger in
diameter than the mirror, pour into a glass measure 10 drams of the
silver solution, add next 10 drams of the ammonia, then 20 drams of
potash; if the potash turns the mixture thick, pour it backwards and
forwards into another vessel, or stir it with a strip of glass, or a
glass rod, for half a minute; if the mixture does not turn clear
(which it will not do if it has turned very thick on adding the
potash), add cautiously, drop by drop, some of the ammonia solution,
agitating it till it just clears; do not filter unless there are a
great many floating particles through using unfiltered water, the
floating particles cause minute black spots, which are, however, of
little consequence, as their action is only the loss of so much
light. Measure 20 drams of the sugar—and the mirror being ready to
dip (the amount with the sugar added must be the required quantity
previously ascertained), add the sugar, stir well, and immerse when
the mixture begins to turn dark ink colour.

When silvered, well wash the mirror with water of the _same_
temperature as itself (it may be safely sponged with a lump of
cotton wool), and stand it on its edge on blotting-paper to dry.
Drops of water standing long on it when drying will cause stains,
which will not readily polish off, and indeed these should not be
polished, as it is not right to polish one part more than another;
so it is best to leave them, or if this is objected to, re-silver
the mirror, when standing it in the sun and wind will soon dry the
surface, but be careful not to let the dust settle on it.

Do not warm anything; if the weather is cold, everything may be left
many hours in a warm room, but the _equal_ temperature is of the
utmost importance—the actual temperature is not of much consequence.
More failures are due to unequal temperature than any other cause in
the hands of the amateur. One careful and clever amateur informed me
that he had failed six times, but on the seventh, by attending to
the advice given above, the silvering was a perfect success, and all
seemed then as easy and certain as it had before seemed uncertain
and difficult.


      THE FINAL ADJUSTMENT OF A NEWTONIAN REFLECTOR ON A STAR.

The adjustments being as near correctness as can be seen by the
usual method of procedure—of which the fullest details are given in
my little book, the telescope is ready to try on a star. If all does
not appear satisfactory on first observing the star, do not disturb
the adjustments for a while, but wait until the air is steadier,
when perhaps it will be quite satisfactory. If not, turn it on a
bright star; if the adjustments are at fault, the black shadow of
the flat, when the star is out of focus, will not be central in the
slightly expanded image, but will be on one side of the expanded
disk. Use a power of 200 to 300.

If the black spot is near one of the sides corresponding with major
axis of flat, the side screw will put it right. We will assume that
the black spot is nearer the edge of flat nearest the mirror, and
that the eyepiece is beyond the focus proper for the star; then
_unscrew_ the side screw. If the spot is nearer the other edge of
flat, _screw it up_ little by little, taking the hand out of the
telescope each time, and see what the effect is. The movement and
alteration can be watched while the hand is in the tube. If the spot
is seen either the top or bottom of the flat that is in the
direction of the diameter of tube, the middle screw must be slightly
loosened and the flat revolved. Let the screw just bite so as to
hold, and tighten it when correct. The definition of a star should
now be perfect, and by daylight observe the adjustments; it may
appear that the reflected circles are not concentric, but if the
definition on a star is good in still air, consider the appearances
correct adjustments, except that the reflection of the black spot on
mirror may be made concentric. It sometimes happens that a
persistent and rigid centreing of the reflections on _face of flat_
are not the positions for best definition, perhaps from a slight
optical eccentricity somewhere in the instrument.

The adjustments of a reflector are soon familiar and easy, and there
is this to be said, the adjustments can be manipulated upon to any
amount without the slightest injury to the instrument; there is no
danger of any sort, and the instrument can be perfected in its
adjustments by daylight, and this makes it both pleasant and
convenient to leisurely work at, for experience sake. The instrument
need not be out of doors either, unless an artificial star from a
black pin’s head—which is better in _strong_ sunlight than a
thermometer bulb—is to be used instead of a star at night, if so let
it be as high as possible.

Be careful not to screw up the small screws too tight, as the fine
threads are liable to be spoiled and the screw made useless.


      THE DURABILITY OF SILVER FILMS.

It sometimes happens that the films do not last so long as they are
expected to do, that is, they sometimes lose their splendid lustre
sooner than they should do. When it is remembered that though the
process of silvering is an easy operation to perform, yet it is a
delicate chemical one, in which good results are best obtained when
several good conditions all meet together, this is not to be
wondered at, but it is certain the instructions given above will
reduce the chances of failure to a minimum, and imperfect results
will be rare. The silver usually lasts a long time. I know silver
films that have been in use for ten years.

Do not suppose that a long and badly worn surface will fail to show
the detail and colours of the planets, the fullest detail also of
the moon or the stars. It is surprising how long a silvered surface
will continue to do its full work while its appearance is much
deteriorated; picking up faint points of light that are near the
very limit of its aperture and power, seem alone to require the
perfect and fresh film. I know silver films that have been in use
for seven years and have not been ever re-polished.

That the Silvered Glass Reflecting Telescope is giving satisfaction
and is capable of performing the best work of a telescope—being
durable, convenient, and perfectly efficient—may be gathered from
the selection of a very large number of satisfactory and most
gratifying letters received by the writer; and it has been most
encouraging to find in all cases the observer is most eager to
express his entire satisfaction, and especially so where so many
have been prejudiced, in the absence of experience, with feelings of
doubt as to their _complete_ efficiency, and many, again, having
used fine refractors.

It will be seen, too, that many have commenced with a small sized
reflector, and gone on increasing their optical power until they
have obtained a large and powerful instrument, imposing indeed as
compared with what was considered a powerful instrument less than
half a century ago, and at a fraction of its cost.

The gratifying success which I have achieved, attested by the
universal satisfaction given by the instruments supplied by me, is
the result of unwearying labour and untiring patience; every
speculum, large or small, being figured with my own hands.

I have every facility for setting up instruments, and for testing,
working, and regulating them in every part on celestial objects. The
optical parts are, therefore, not merely tested separately and
subsequently mechanically adjusted, but each and every instrument is
put together and optically and mechanically tested, as a whole,
before it is permitted to leave the workshop.

Every speculum is most carefully figured, and confidently guaranteed
perfect _to the extreme edge_.

The employment of “stops” of any kind is quite unnecessary, except
on bad nights, when the aperture must of course be suited to the
degree of steadiness of the air. For, whether the instrument be a
reflector or a refractor, the aperture and power used must of
necessity be limited by the atmospheric conditions under which
observations are made.

It should, however, be remembered that the reflector having not only
a much larger aperture than a refractor of same focal length, and,
being open to the influence of the external air, is not only
affected by a relatively larger column of air, but is affected in a
different way. It frequently happens that reflectors of 6 in. to 18
in. aperture, are of same focal length as 5 or 6 inch refractors.

These considerations will explain the occasional use of stops, and
the expediency of having them ready to use when they can be of
temporary advantage. There are nights in our climate when a 6 inch
aperture may be the largest that can be used with satisfaction or
advantage; indeed it used to be accepted as an incontrovertible fact
that an aperture of G inches was the largest that could be used on
_average_ nights in our country. But there are also not a few nights
when large apertures, bring great gain to their fortunate
possessors.

It is obvious that, _mutatis mutandis_, these conditions must affect
refractors as well as reflectors, with perhaps this difference, that
in the case of a reflector the rays pass down the tube and infringe
on the speculum as a column of parallel rays; consequently all the
external rays of the column travel near the surface of the tube for
its entire length. This being so, it is obvious that until the
internal and external air and the metal tube have time to equalize
in temperature, it will be advantageous, in all work requiring high
powers, such as the examination of difficult double stars, to “stop
off” for a time the _extreme edge_ by a small diaphragm.

This will occur especially on frosty nights after a warm fine day.
When the telescope is in the open air, ice will not infrequently
form on the top of the tube, and the effect will be at once obvious
in the irregularity of a star image at the edge corresponding to the
top of the tube. The use of a small diaphragm will at once obviate
this defect and give perfect images. On such nights a wooden tube is
preferable to a metal one. It has been frequently my experience,
when finally testing an instrument, that when I have been
dissatisfied with its performance, and in order to trace the cause
of the apparent defect, have removed the mirrors to my wooden
testing tube, I have found every defect removed, and imperfect
replaced by perfect images. The explanation is simple. Not only is
the wooden tube much larger in diameter than the specula, but wood
is of itself less sensible than metal to differences of temperature.

To make the tubes some 2 or 3 inches larger in diameter than the
speculum would cure this evil, but it would involve various
inconveniences and expenses in structure, which would more than
outweigh the advantage of overcoming a hindrance which is after all
only temporary and occasional.

The experiment of perforating or ventilating tubes has now been
thoroughly and exhaustively tried, with the result that there is a
fairly general consensus of experienced opinion against their use.
The advantages are merely theoretical; the disadvantages are grave.
Among them are the admission of cross reflections in every
direction, the admission of dust, imperfect protection of the
mirrors, and a decided loss of strength and rigidity to the tube.



      CATALOGUE OF Silvered Glass Reflecting Telescopes, &c.,

      AND THEIR ACCESSORIES,

      OCTOBER, 1880.


G. Calver, while introducing the list of prices below, has the
greatest confidence in calling the attention of the practical
astronomer and the amateur to the very moderate prices charged,
considering the principle and style of the mounting, and the firm
and well-fitted arrangements in all the parts.

The principle of the mounting is that which is the most convenient
to use, and with the greatest degree of steadiness with the easiest
movements. Fig. 1 is the _best mounting ever applied to the
Reflecting Telescope_.

He is also able to state that, with his processes and special
facilities for working large specula, and substantially mounting
them, he is prepared to construct automatic equatorials of large
sizes, and with any special arrangements that may be required.

Fig. 1 is a very excellent mounting, and admirably suited for large
instruments, especially when clock-power is applied; and as now
manufactured by G. CALVER, is the most complete and reliable, its
details of construction being such as to give the greatest freedom
of motion and steadiness. For large sizes the top of polar axis
works on friction rollers; and, as a superior German stand, its
arrangements and means of astronomical as well as optical
adjustments, are such as to make it an instrument of precision.

To ensure these qualities many well considered
arrangements—entailing careful and expensive workmanship—must be
provided; details that do not easily admit of description in an
ordinary catalogue, or can be shown in an engraving, but are duly
appreciated by the observer, who will find their value by practice.

The cradle bar is compound with fine screw movement for perfecting
collimation, but to make this adjustment perfect, the telescope tube
must be centred in a powerful lathe, and the cradle and solid metal
rings in which the tube revolves (see illustration) has to be turned
and fitted with true flanges or working bearings; the mechanical and
optical centres will then coincide.

The hour circle, to be truly divided, must be truly made, and is a
solid wheel of good substance, working on a secondary axis, and
rotated by mechanical means, truly concentric, with a very strong
polar axis.

The declination circle has fine tangent screw movement, with double
action for setting the readings by milled-headed screw, and also
long driving rod from the eye-piece to set and adjust the object in
centre of field. There is slow hand motion, by a separate wheel in
right ascension.

The clock-power is connected and disconnected instantly, by touching
with the finger a small lever, conveniently placed at a small door
in the clock case. The clock will go at exactly the same rate,
whether it is driving the telescope or not, and the latter begins to
move at the proper speed the instant the lever is moved, and the
connection of the telescope and clock made, which is instantly
effected by another lever.

                                                              £  s. d.
  14, 15, to 16 inch Speculum mounted as (Fig. 1), with
      rotating hour circle reading to 5 seconds and decimation
      to 1 minute (the diameter of the circles never less than
      that of the Speculum, and often larger)

  8 powers, from 50 to 700, with first-rate and very powerful
      driving clock, first-class instrument,
      and complete                             from £250 to 350  0  0

  17, 18, to 20 inch Speculum, with 10 powers, from 50 to 800,
      including Kellners, Huyghenians, and Achromatics,
                                              from £360 to  500  0  0

  22 to 24 inch Speculum                      from £600 to  700  0  0

  30 inch Speculum, with 12 powers and position micrometer,
      and transit eye-pieces                               1000  0  0


Prices will be forwarded for special arrangements in any of these
large sizes.

                                       £  s. d.
  Driving Clocks for 6 to 8 inch      35  0  0
        〃     〃    12 〃 18 〃        40  0  0
        〃     〃    20 〃 30 〃        50  0  0


These are fitted with governor, regulator, and self-adjusting break.
They are made of gun metal and steel, and every wheel is cut. They
drive with most excellent regularity, and are, when desired, made to
beat seconds on a bell. The whole is enclosed in a mahogany frame,
with glass panels.


Fig. 2 admits of equal completeness, &c., but the stand is not so
convenient for clock-power.


SILVERED GLASS EQUATORIAL TELESCOPES, very substantially and well
fitted as (Fig. 2). All these equatorials have revolving body.

                                                              £  s. d.
  5-1/4 inch Speculum, from 4 to 6 feet focus, with 7 inch
     hour circles, reading to 5 seconds of time, and
     declination circle reading to 1 minute, 2 powers        30  0  0

  6-1/2 inch Speculum, of from 5 to 6-1/2 feet focus,
     10 inch rotating hour circle, reading to 5 seconds of
     time, and declination circle to 1 minute of arc, with
     3 powers--100 to 500                                    45  0  0

  8-1/2 inch Speculum, as above, with 10 inch circles,
     4 powers                                                70  0  0

  10 inch Speculum, as above, with 10 inch circles,
     5 powers                                                90  0  0

  12-1/2 inch Speculum, as above, with 10 inch circles,
     5 powers                                               120  0  0


The EDUCATIONAL REFLECTOR is a plain and very steady and
satisfactory instrument, mounted on (Fig. 2) stand, without circles,
has revolving body, and made so as to be portable.

                                                              £  s. d.
  8-1/2 inch Speculum as above, with 3 powers                40  0  0


The POPULAR REFLECTOR (Fig 3), with Angle-Block stand, with
endless screw-motion to follow the stars with equatorial motion.

                                                              £  s. d.
  5-1/4 inch Speculum, of from 4 to 6 feet focus,
      with 2 powers                                          15 15  0


These are also made with rotating body.


Reflecting Telescope on Alt-azimuth Stand, fitted with silvered
glass Speculum, and provided with two eye-pieces.

                                                             £  s. d.
  5-1/4 inch Speculum, 4 to 6 feet focus                    19 10  0
  6-1/2  〃      〃    5  〃 6-1/2 〃                         25  0  0
  8-1/2  〃      〃       〃 6-1/2 〃                         33 10  0
  10     〃      〃       〃 7     〃                         50  0  0
  12-1/2 〃      〃       〃 8     〃                         70 10  0


      Silvered-Glass Specula (_unmounted_).

      THE FINEST QUALITY GUARANTEED.

                                                £  s. d.
  5-1/4 inch diameter, 4 to  6 feet focus       5  0  0
  6-1/2        〃       4 〃  6-1/2 〃           6  5  0
  8-1/2        〃         〃  6-1/2 〃          13  0  0
  10           〃         〃  7     〃          25  0  0
  12-1/2       〃         〃  8     〃          38 10  0
  14           〃         〃  8     〃          55  0  0
  16           〃         〃 10     〃          75  0  0
  18           〃         〃 12     〃         100  0  0
  20           〃         〃 12     〃         130  0  0
  22           〃         〃 15     〃         165  0  0
  24           〃         〃 18     〃         200  0  0
  26           〃         〃        〃         250  0  0
  30           〃         〃        〃         300  0  0
  36           〃         〃        〃         400  0  0


      Silvered-Glass Diagonal Mirrors (_unmounted_).

      FINEST QUALITY GUARANTEED.

                                                                £  s. d.
 1 inch in the minor axis, or narrowest diameter of the ellipse 1  0  0
 1-1/2         ditto           ditto             ditto          1 10  0
 2             ditto           ditto             ditto          2  0  0
 2-1/2         ditto           ditto             ditto          2 10  0
 3             ditto           ditto             ditto          3  3  0
 3-1/2         ditto           ditto             ditto          4  4  0
 4             ditto           ditto             ditto          5  5  0


      Silvering and Polishing Specula.

                           £  s. d.
   5     inch              0  6  0
   6-1/2  〃               0  8  0
   8-1/2  〃               0 10  6
  10      〃               0 15  0
  12-1/2  〃               1  1  0
  Diagonal Planes  3s. to  0  5  0


      ASTRONOMICAL EYE-PIECES.

      OF BEST QUALITY.

Huyghenian Construction of the following magnifying powers on a 6-1/2
feet focus object-glass:—

                                       £  s. d.
  35, 60, 90, 130, 180, 200       each 0 15  0
  320, 450                             1  1  0
  610                                  1  7  6

      All fitted with Sunshades.


      Improved Achromatic, Ramsden’s Construction.

                                      £  s. d.
  90, 130                     each    1  0  0
  189, 250                            1 10  0
  320, 450                            1 12  6
  610, 750                            2  2  0
  850                                 2  2  0


      Kellner’s Construction.

                                      £  s. d.
  30, 58, and 80               each   1  5  0


      Solar Eye-Pieces.

                                                             £   s. d.
  Solar Diagonal, with true plane                            1  12  6
  Barlow’s Lens                                              1   1  0
  Day Erecting Eye-piece                                     1   5  0
  Coloured Eye-piece cap for observing the Moon              0   4  0
  Transit Eye-pieces, for use with Equatorials   £1 1s. to   2   2  0
  Adjusting Piece                                            0   2  6


_Good Instruments will be taken in exchange, and liberally allowed
for._


      GEORGE CALVER,

          HILL HOUSE, WIDFORD,

              CHELMSFORD, ESSEX.


      LETTERS AND EXTRACTS FROM THE FOLLOWING GENTLEMEN.

      _From_ W. E. PARKINSON, Esq.

                              11, WELLINGTON PARK TERRACE, BELFAST,
                                                  _July 7th, 1876_.

DEAR SIR,—The night before last was a clear night, and I got the
6-1/2 inch out, and though the air was not good when using a 3-1/4
inch refractor, I was much pleased with the performance of the
mirror.

Mr. W. came up about eleven o’clock and stayed till one; we got it
on Saturn, and although rather low it was really a fine sight—Mr. W.
was much pleased.

The moon being near to full we could not do much with faint points
of light.

                                                   Yours sincerely,
                                                        (_Signed_.)


Mr. G. CALVER.

       *       *       *       *       *

      _From_ F. G. LEMMAN, Esq.

                                        74, HAGLEY ROAD, EDGBASTON,
                                             _November 27th, 1876_.

DEAR SIR,—I have now got the 5 inch speculum fairly into adjustment,
and I am well pleased with it. Last night, the sky being clear for a
short time, I turned it on the moon; the definition of minute
craters was all that could be desired. I hope to have better
opportunities.

                                                   I am,
                                                      Yours truly,
                                                        (_Signed_.)


Mr. G. CALVER.

       *       *       *       *       *

      (_From the same Gentleman._)

                                        74, HAGLEY ROAD, EDGBASTON,
                                             _November 21st, 1876_.

DEAR SIR,—I have mounted the 5 inch speculum on a simple equatorial,
and it works well. I am sure it will turn out a fine glass, and I
shall not regret the time and pains I have spent over it. It is not
quite in adjustment yet, when it is it will afford me a treat. I
have just tried it once on the Orion Nebula and Trapezium, details
of Nebula well seen, and the 5th star in Trapezium easy.


                                                   I am,
                                                      Yours truly,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ D. C. CARMICHAEL, Esq.

                                          DOWLAIS,
                                             _December 27th, 1876_.

DEAR SIR,—I have thoroughly tested the speculum, and am pleased to
tell you it stood its trials well.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

                                           ST. DENIES, SOUTHAMPTON,
                                               _August 14th, 1876_.

DEAR SIR,—With reference to your enquiry as to the performance of
the 6-1/2 inch reflector, I have pleasure in stating that I am
perfectly satisfied. It readily divides the test objects, and shows
delta Cygni with as low a power as 160. The comes to Sirius may be
considered an atmospheric test, perhaps, but I have repeatedly seen
it. Your stand I find very steady and convenient; altogether I can
fairly say that I consider that I have an instrument of considerable
power at a comparatively small cost. I now find the attempt to
observe with a refractor the reverse of pleasant.

The owner of a 3 inch refractor, after using my reflector, writes
that he envies me its power, ease, definition, and comfort in
observing.

                                      I am, dear Sir,
                                                 Yours truly,
                                                           A. H. S.

       *       *       *       *       *

      _From_ W. L. LANCASTER, Esq.

                             25, HAMILTON TERRACE, ST. JOHN’S WOOD,
                                                  _May 26th, 1877_.

MY DEAR SIR,—I have much pleasure in informing you that the very
first time I saw Saturn through your 6-1/2 inch reflector, the
definition of the planet was far superior to anything I had observed
before, even with a good 4-1/4 inch refractor; and on another
occasion I was greatly pleased with the clear and easy view of the
“Comes” to ε Boötis. But even without including the stars, the views
of Saturn and Jupiter through my 6-1/2 inch mirror do _alone_ (in my
opinion) well repay the cost of the telescope.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      From A. A. COMMON, Esq., F.R.A.S.

                                       37, EATON RISE, EALING,
                                             _February 13th, 1877_.

DEAR SIR,—I like the 18 inch speculum, and I think it as good as it
can be, and if the larger one is as good I shall be delighted with
it.[1] It gives beautiful star images; I see Sirius as a brilliant
dot, a glorious object without ray or flares of any kind. I never
saw it so well before.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

Footnote:

[1] This alludes to the 37 inch, then under consideration; and I may
now add that Mr. Common is perfectly satisfied with it, and
“consider it a _very fine_ mirror.”


       *       *       *       *       *

(_From the same Gentleman._)

                                            37, EATON RISE, EALING,
                                              _February 3rd, 1877_.

DEAR SIR,—I have tried the 18 inch speculum on some tests, and
especially the satellites of Uranus, and it appears fine, very fine.
What I have done in photography promises well.

                                                       Yours truly,
                                                        (_Signed_.)

Mr. G. CALVER.

       *       *       *       *       *

      _From_ J. L. LANCASTER, Esq.

                                           SOUTHEND-ON-SEA,
                                                _March 17th, 1877_.

MY DEAR SIR,—Circumstances have prevented me from making many
observations of late, but I am more confirmed in my opinion that my
telescope of your make is a very fine instrument (a 6-1/2 inch). I
heartily wish you success, which I feel sure you will obtain, as you
are so painstaking and turn out a thoroughly reliable article. I
shall be curious to compare my brother’s telescope with mine.

                                                  Sincerely yours,
                                                        (_Signed_.)

Mr. G. CALVER.

       *       *       *       *       *

      _From_ The REV. W. P. MATTHEWS.

                                           GORLESTONE,
                                                _March 30th, 1875_.

DEAR SIR,—You have asked me for my opinion of the 10 inch speculum.
I have tested it, and can speak in the highest terms of its
performance. Definition in good air is as near perfection as it is
possible to imagine. Such tests as ζ Cancri, γ^2 Andromedæ are well
divided. The 6th star in the Trapezium stands out well clear of its
brighter neighbour. On the moon any power may be applied, only
lessening the light, but retaining sharpness of outline. I have
tried a good many telescopes, but never yet saw these 10 inch
mirrors surpassed. The image of a star disc expanded on each side of
the focus is of as nearly the same appearance as possible.

                                                      Yours truly,
                                                        (_Signed_.)

       *       *       *       *       *

                                            416, BRIXTON ROAD,
                                                _April 20th, 1875_.

DEAR SIR,—In compliance with your request, I send particulars of my
observation on φ Draconis. It was about 12.45 this morning when I
directed my 8-1/2 inch to this object, the air was very unsteady, in
fact not nearly so good as some nights lately, and I well divided it
with a power of 450. I then used a 6-1/2 inch stop, which I found
very much increased the steadiness of definition.

                                           Yours very respectfully,
                                                              P. H.

       *       *       *       *       *

                                                 _July 10th, 1874_.

DEAR SIR,—I tried the 6-1/4 inch mirror I had from you for the first
time last night. The night was not a good one for definition, but I
was very much pleased indeed with its performance.

                                                       Yours truly,
                                                           C. H. W.

       *       *       *       *       *

      _From_ H. SADLER, Esq., F.R.A.S.

                                         HONITON RECTORY,
                                             _December 23rd, 1874_.

DEAR SIR,—I have been wishing to tell you how pleased I am at the
performance of your mirror. Many thanks for your kind offer to
change the mirror if needful, but I think it could hardly be better
than it is, its performance on different double stars is most
excellent. I have examined nearly 100 of these since September with
the 6-1/2 inch, most of them very difficult, but the mirror came out
well under all tests. I send you a list of some of the objects I
have examined.

                                                       Yours truly,
                                                         H. SADLER.

       *       *       *       *       *

π _Aquilæ._—Divided, power 80. 14-^m. Webb might have been rated
15-^m. [6-^m., 7-^m. 1″·5.]

             A      B   C   A-B  A-C
δ _Aquilæ._—[3-1/2, 16, 14, 96″, 194″.] Comites easy, 3 other
excessively minute ones, not shown by the 11 inch refractor with
which P. Smyth measured B.C. Found 6-1/2 in. Sept. 12th, est.
± 17 mag. 100″ to 110″.

ζ _Persei._—My friend “Linea” sees two minute stars with 4·28 in.
Wray, not in Webb, and Wray himself sees an excessively difficult
companion. I see these 3 stars easily with 6-1/2 in. (Wray says his
companion is “very difficult with 7 in. refractor, really only a
glimpse star, even with the best atmosphere”), and have added two
more stars to the group.

β _Delphini._—Close double discovered by Burnham, est. 0″·7. In
contact 6-1/2 in., power 430.

η _Coronæ Borealis._—Very low, long past meridian, in contact 164
power.

              _a_    _b_  _c_  _n_
β _Equalei._—[5-1/2, 13,  14,  16: _a-b_ 35″, _a-c_ 50″ _b_-B 3″.]
16-^m. not seen, Webb 9-1/3 in. Just divided 164, easy 430 power.
Two other companions (not seen by Smyth or Webb?)


μ _Andromedæ._—The 16-^m. comes, a very difficult test, easy; other
comites (not seen by Smyth or Webb?) seen.

Companion to Vega pretty easy, Nov. 12th, 37m. after sunset.


                          _a_    _b_  _c_  B  _a-b_  _b_-B  _a-c_
_P._ 178 xx. _Delphini._—[7-1/2, 8,   16,  9: 14″·3, 0″.7,  20″.]
Smyth 16 by evanescent glimpses; easy 164 power, 6-1/2 in. 8-^m.
well elongated in direction of 230°, power 430.

       *       *       *       *       *

      _From_ H. BLYTH, Esq.

                                       REGENT ROAD, GREAT YARMOUTH,
                                              _October 24th, 1874_.

DEAR SIR,—Doubtless you have anticipated hearing from me, relative
to the 10 inch telescope, but the weather has been so indifferent
for delicate astronomical work, that it has not yet had a fair
trial.

In middling good air, when I could use a reduced aperture with
satisfactory results, the star images reminded me of the 6-1/2 inch,
which I considered so superb a mirror that nothing could surpass its
fine performance either on stars or planets.

With the recollections of the truly splendid views I had of Jupiter
last season, I count much to see him with the 10 inch.

                                                      Yours truly,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ T. AYERS, Esq.

                                       REGENT ROAD, GREAT YARMOUTH,
                                              _February 2nd, 1875_.

DEAR SIR,—In reply to yours, I have not had a really good night to
test severely the defining powers of the 10 inch mirror, but judging
from the few difficult objects I have seen, the mirror promises
well, and I have no doubt of its excellence.

I had a fine view of the grand nebula in Orionis, and noticed that
the 5th and 6th stars were quite plainly seen, when the aperture was
reduced to 5-1/2 inches. I consider your stand a great improvement,
being very convenient and steady.

                                                      Yours truly,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ THE REV. A. P. ARNOTT.

                                              AM STREET, EDINBURGH,
      8-1/2″ ALT. AZIMUTH.                   _February 25th, 1878_.

DEAR SIR,—I have found no difficulty in putting up the instrument,
and the adjustments do not appear to be hard to manage. It is a very
beautiful instrument, and the case with which its movements are made
is extraordinary.

                                           I am, dear Sir,
                                                Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ J. SLATER, Esq.

                                          TOWN HALL SQUARE, BOLTON,
                                                 _September, 1877_.

DEAR SIR,—Last night, through a break in the clouds, I managed to
get my first look with the telescope (an 8-1/2″). I turned it on
delta Cygni. The definition was rather fluttering, but a 6-1/2 in.
stop enabled me to see it well with 170; the first time I have ever
divided this star[2] the colour was obvious. I then tried Pi Aquilæ,
which was beautifully divided. I am much pleased with the instrument
and its performance, and when I do get a fine night I expect great
things from my 8-1/2 in.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

Footnote:

[2] The observer had used an 8-1/2″ reflector, however, for some
years.

       *       *       *       *       *

      (_Another Letter from the same Gentleman._)

                                              BOLTON,
                                                  _December, 1877_.

DEAR SIR,—As to the adjustments of the 8-1/2 in., I have had very
little trouble, and I have tried it again on a few objects, a few
nights ago, and with a 7 in. stop, and a power of 300, I split Zeta
Cancri and the close double _sf_ Castor; with the full aperture they
were very easy. I have also split Gamma Andromedæ with 7 in. stop,
and on a very fine night. I believe 6-1/2 in. would do it.

I just got a look, on November 7th, at the shadow of Titan, on
Saturn’s disc; but was driven inside before I could observe the time
of its passing the centre. I have seen the Moon on two occasions
with the finest definition I ever saw. Altogether I am highly
pleased and proud of my telescope. I have not yet tried many faint
objects; still I saw the Crab nebula in Taurus much nearer Lord
Rosse’s drawings than Herschel’s, as given by Chambers.

                                                 I am, dear Sir,
                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ G. BILLINGTON, Esq.

                                                WELLWICK, WENDOVER,
                                                       _July 19th_.

DEAR SIR,—I am perfectly satisfied with the mirror, a 6-1/2 in., now
that I have tried it with _your_ flat, and I have no difficulty in
seeing star disks when the air is good.

                                                 I am, dear Sir,
                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. S. TOMLINSON.

                                  CARLISLE TERRACE, MALAHIDE, 1877.

DEAR SIR,—I write to tell you that I was very much pleased indeed
with last night’s observations with your 18″. The star disks were
good and well condensed, and stray light well gathered in, and when
a good night comes I have no doubt of it.

The markings on Mars were well defined. I find the advantage of a
large aperture shows itself. I have no doubt I picked up the outer
Satellite, but cannot be certain till to-night, if I am permitted to
see it. The only objection I have is its short focus, as it
seriously complicates my labours in matching the secondary convexes
for the Cassegrain form—if you can help me in the matter of a longer
focus; if not I am satisfied and thankful, and must only proceed to
the testing process inch by inch.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From the same Gentleman._

                                        CARLISLE TERRACE, MALAHIDE,
                                              _November 6th, 1877_.

MY DEAR SIR,—I had intended to write to you before, but, from
various duties, I have been obliged to postpone it from day to day.
I have been working steadily, however, with your 18″, and I like it
the more I use it. The figure is wonderfully perfect, and the
definition of planetary details and markings most admirable.

On four occasions I have seen the Satellites of Mars; of these I can
feel quite certain of two, for it was held sufficiently long to
perceive a marked change in position angle. The intensely small
companion to _a_^2 Capricorni I have well seen, cleanly separated,
and that in strong daylight. I am anxious for a good night to attack
τ Orionis. During these observations I have been using the telescope
as a Newtonion during my work at the convexes; but my labours have
been pleasantly intercepted by the magnificent and gorgeous views of
the star clusters and nebulæ—more beautiful and startling than I
could possibly have imagined, and surpassing far anything I had ever
pictured to my mind.

                                                 Yours very truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ MAJOR-GENERAL ADDISONS, C.B.

                                                      MELTON, 1878.

SIR,—You will be glad, I know, to hear that I had a very
satisfactory evening with the 18 in. equatorial yesterday, and the
clock kept it in the field without vibration of any sort.

                                                 Yours obediently,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ J. T. STEVENSON, Esq.

                                       AUCKLAND, NEW ZEALAND, 1877.

DEAR MR. CALVER,—Since writing to you I have been observing with the
6-1/2 in. equatorial telescope, and I have much pleasure in
informing you that I am greatly pleased with its performance. The
definition of the planets is beautiful.

I am happy to inform you that I have found a most minute crater in
Picard _a_, it is much smaller than the test crater (mentioned in
Cel. Obj., by WEBB, page 83) in same formation. I wrote to Mr. WEBB
about it, and since then I have seen it distinctly; it is another
proof of the excellence of your telescope.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ J. C. HARKER, Esq.

                                                      KENDAL, 1878.

DEAR SIR,—After four months use of the telescope I had of you (an
8-1/2 in.), I am able to tell you that I am much pleased with its
great excellence. The definition of the mirror is very fine, and its
performance on the Moon being superb, with so high a power as 700.
The stand I find very steady and convenient, and the screw motions
very smooth.

                                                 I am, dear Sir,
                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ E. A. FRY, Esq.

      BIRMINGHAM, 1878.

DEAR SIR,—I write to tell you that I like the telescope very much
(5-1/4 in. equatorial); the mirror is, as you say, a gem, and it is
quite a treat to look at the mysteries above. Saturday was a
glorious night, though the Moon was rather too bright. Altogether I
am quite satisfied with the telescope, and the finish is first-rate.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. J. M. COATES.

                                   THE GODDARDS, MOULTON, SPALDING.

DEAR SIR,—I am able to report satisfactorily on the mirror. On
Saturday night last I divided μ^2 Boötis, power 300, with the
8-1/2″.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From the same Gentleman._

                                   THE GODDARDS, MOULTON, SPALDING,
                                              _January 18th, 1879_.

DEAR SIR,—I have been waiting for opportunities for testing
observations, but there have been few nights when the weather and
leisure time have concurred in giving me a chance. However, I can
say this much, that in lunar work I have had much pleasure from the
excellent definition given by the 8-1/2 in. I had some fine views of
Copernicus under high powers not long since, and am anxiously
awaiting opportunities for closer study of a particular region.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ FRANK C. DENNETT, Esq.

                                 10, TERMINUS TERRACE, SOUTHAMPTON,
                                             _December 10th, 1878_.

DEAR SIR,—The 5-1/4 in. is beautiful. Last night there was a slight
frosty fog, and the air was very very steady, in fact I only
remember about one such night since November, 1875. Saturn was sharp
and hard, and the shadow of the ring intensely black, with all
powers from 168 to 372, and even with 550, obtained by removing the
field lens of 372. The very broad polar caps presented a bluish
grey, rendered more visible by contrast with a fine penumbral line
of a very slightly brownish grey close to the south border of the
ring, and which seemed to be diffused on the south border (_i.e._,
the line was diffused). I should fancy the line here referred to was
less than 1″ of arc broad; considerably less!

Turning from Saturn, I looked at ε Arietis, the present distance of
which is only 1″·17; with all powers, from 213 upwards, the
components were visible as two tiny points of light thoroughly
divorced, and with 288 power, reminding one of ε^2 Lyræ, as seen
with 120 on a 2-3/4 in. achr., only the discs seemed freer from
rings.

Later in the evening, when the definition was more fluttery, η
Orionis shared the same fate as ε Arietis, being well separated with
the same powers. The present distance of this star is only 1″·12.
Recently I divided this star with a 4-1/2 in. stop on the mirror,
power 288. I have seen ε Arietis well with the same stop too. I
think I have told you before that the 5-1/4 in., with 372 power, was
successful in dividing ε Equulei, whose distance is only 0″·97. This
is the closest star I have yet divided.

The Moon is fine too! Last night I caught a large ring close to the
terminator, near the south pole (for the Moon was only about 2-1/2
hours past full), which was looked at over the northern wall; the
view was beautiful, such gradations of light and shade, interspersed
with greys of different hues, which render the object scarcely
describable. The finest clefts and tiniest craterlets are rendered
visible. It is a puzzle to me how anyone in the possession of £16 or
£17 can go buying a refractor of from 2-1/2 to 3-1/4 in. aperture in
preference to a silvered mirror. It must be from sheer ignorance of
the beautiful views given by the latter, which is superior in every
way.

I do not think there is any other point on which I need touch now,
so I must beg to remain,

                                            Dear Sir,
                                                 Yours very truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. JEVON J. MUSCHAMP PERRY, M.A., F.R.A.S.

                                      ST. PAUL’S VICARAGE, ALNWICK,
                                             _December 20th, 1879_.

MY DEAR SIR,—I was very much interested in reading your account of
the grinding and polishing of the 37″ speculum, in this week’s E.
M., copied from the “Monthly Notices” of the R. A. S. Had I only the
wealth of my neighbours, I would give you an order for the largest
telescope you could construct. Every really good night gives me some
fresh proof of the great excellence of the 6-1/2 in. For instance,
on December 15th, I clearly and steadily saw _Enceladus_. I could
not, of course, have recognized it had it not been that this month’s
“Observatory” gave diagrams of the positions of the five inner sats.
of Saturn, for 8 p.m. on every day of this month, and a careful
search for Encel. was fully rewarded by a clear and steady view of
it at that time in its proper place. On this feat the Rev. T. W.
WEBB warmly congratulated me, and said that he had seen Encel. with
his 9-1/3″ “With,” but only when Saturn was hidden behind a bar. I
saw it clearly in exactly its proper position _without_ hiding the
planet—power 400. I have also had several good views of Mr. WEBB’S
new nebula in Cygnus, and have sent him drawings of the field, which
he confirms. I have also made some fine drawings of Jupiter and
Mars. On December 12th, 11 p.m., I tackled σ 749 (in Taurus), a very
difficult test for my aperture, only 0·8″, and _perfectly_ split it
with power 300. The night was superb. When you consider that the
theoretical limit of dividing power for a 6-1/2″ is only 0·7″, I
think I have done well to split a star 0·8″ in our climate.

                                                  Faithfully yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ G. FERGUSON, Esq., M.D.

                             ALTIDORE VILLA, PITTVILLE, CHELTENHAM,
                                                 _June 26th, 1879_.

MY DEAR SIR,—I write to tell you that Thursday night being very
fine, I had a good opportunity of trying the (an 8-1/2″) mirror on
Jupiter, although this planet was lower than it should have been to
give the fairest trial. Well, I can only assure you that, despite
the low position, I never saw it so beautifully before. The contour
of the clouds, particularly one orange one, _sf_, the delicate
lines, and the colouring of the belts, were all seen with a
sharpness which I had believed scarcely attainable, and proving that
the result of your labours has been to effect a very real
improvement in the speculum. Notwithstanding the good planetary
definition, the air was not tranquil enough for seriously attacking
really difficult doubles; still I was much pleased with its
performance on π Aquilæ.

                                                       Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From the same Gentleman._

                                                       _July 27th._

Yours of July 25th duly to hand. I have the speculum adjusted in the
“pink” of accuracy. Star discs are small and round, with concentric
diffraction rings, and quite rayless except in the case of the very
brightest stars, and even with these the rays are very trifling. But
for the diffraction rings, which I fancy a really good night will
mostly get rid of, I should, I feel sure, have readily divided η
Coronæ.

The Moon last night, though very low, was seen with most gratifying
ease and sharpness. Altogether you will gather that I am more than
satisfied. I am greatly gratified, and will look forward to great
pleasure as the season advances.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. JEVON J. MUSCHAMP PERRY, M.A., F.R.A.S.

                                      ST. PAUL’S VICARAGE, ALNWICK,
                                                _August 8th, 1880_.

MY DEAR SIR,—You have indeed surpassed yourself, and your
performance is better than your promise. The mirror arrived safely
yesterday, and when I unpacked it I was exceedingly pleased with its
surface and general appearance, but of course that was a small
matter. I waited till night to test it on a close double.

I first tried it on ε Boötis, and although the night was very bad
the definition it gave of the two stars with 450 and full aperture
was admirable, considering the night. After waiting a long time for
clouds to clear away, I turned the tube on that exceedingly
difficult test, δ Cygni. I consider this star to be one of the
severest tests for any telescope, reflector, or refractor of any
aperture in the whole heavens. The performance of the mirror upon
it, with the _full_ aperture, was simply MAGNIFICENT, the small
close companion standing out clearly, well separated from its bright
primary, although the night was not good. I hardly thought it
possible that the fine 18 inch mirror could be excelled. I am bound
to confess that you have excelled it.

To say that I am extremely grateful to you is a very poor expression
of my feelings. I am pleased and delighted _beyond measure_ with the
_super-excellent_ 18-1/4 in. mirror you have sent me. Clouds put an
end to my work last night, but I have no doubt that in the future
every night’s observations will only accumulate proofs of the
exquisite perfection of your handiwork.

                                            Very faithfully yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _Extract from the “English Mechanic,” September 3rd, 1880_.

“The telescope is a silvered-glass Newtonian reflector. There are
two specula, one of 18 in. in diameter, figured by the celebrated
WITH, in 1878, and is a magnificent specimen of that eminent maker’s
handiwork. In fact, I am given to understand that Mr. COOPER KEY
considered that he had attained perfection in this mirror, and of
all men then living there was no better judge than he. The other is
18-1/4 in. in diameter, and was originally figured by Mr. COOPER KEY
himself; but it was only perfect over the interior 14 in., and,
consequently, while the whole aperture could be used on the moon and
planets, this was all of it that could be used upon close doubles. I
determined, therefore, to give this mirror to Mr. CALVER to
re-figure, and, if possible, excel Mr. WITH’S speculum.

“In order that Mr. CALVER might know the extent of his task, I
returned home through London and Chelmsford, bringing with me both
mirrors, which Mr. CALVER tested for himself at the centre of
curvature. After the trial was over, he pronounced Mr. WITH’S mirror
to be an exceptionally fine one, and heartily congratulated me on
the possession of such a beauty. I left the other one with him to be
re-figured.

“And now to come to the most important part of all—the performance
of the 18 in. WITH mirror upon close double stars. Since the
telescope came into my possession, I have never had a thoroughly
good night; but even on an indifferent one, I have, with the _full
aperture_, divided such extremely difficult tests as η Coronæ, μ^2
Herculis, and δ Cygni; and these results were quite sufficient to
show me that the very high reputation of its excellent maker is
worthily and proudly maintained by this mirror. In fact, the
definition it gave one night, when the Scottish Astronomer Royal was
staying with me of ε Boötis, was such, that the Professor
told me I could not expect any telescope, reflector, or refractor,
upon the same object, and on the same night, to do better. However,
I knew Mr. CALVER was doing his very utmost in the honourable and
praiseworthy competition to attain perfection, to give me a mirror
which would bear favourable comparison with Mr. WITH’s. It reached
me about a week ago, and on the same evening I had an opportunity of
testing it upon what I consider to be one of the very severest tests
that can be applied to any telescope, reflector or refractor, in the
northern heavens, that is δ Cygni[3]. To make the test as severe as
possible, I applied the _whole_ aperture at once, with a power of
347. I was surprised and delighted _beyond measure_ with the result.
The small star stood out clearly separated from its bright primary,
and there were two or three diffraction rings round the latter
_unbroken_ in any part, and _equally_ bright all round. I consider
the results which Mr. CALVER has attained in this mirror cannot
possibly be excelled. I measured this star on two separate nights,
and the mean results are pos. 328·9°, dist. 1·29″. I also measured,
with this mirror, another difficult star of the same character,
namely, with a bright primary and small companion, ζ Herculis, with
the following results, pos. 111·3°, dist. 1·03″. I make the
companion of this star a dusky blue, or lavender. As regards the
light-grasping power of the mirror, I turned it, the other night, on
the minute pair between β^1 and β^2 Capricorni, which Sir John
Herschel gave as the test of the power of any telescope and eye to
observe the satellites of Uranus. The night was very unsteady, but
the minute stars of the pair were most conspicuous.”

Footnote:

[3] NOTE.—Mr. Perry does not mean that δ Cygni is one of the most
difficult tests as regards the distance of the components. He has
often seen it with his 6-1/2″ Silvered Glass Reflector, and even
with a stop of 5-1/2″ on the same instrument; but he was surprised
at the beauty and perfection of the images—perfect and unbroken
rings—and he knew that these appearances could not have presented
themselves had not the _figure_ of the mirror been of extraordinary
perfection.

       *       *       *       *       *

      _From_ THOS. WESTLAKE, Esq.

                                                 FORDINGBRIDGE,
                                                      _June, 1880_.

MY DEAR SIR,—I wrote you last evening, and afterwards had my first
trial with the telescope (a 10 in. Alt Azimuth). It turns out a
beauty. I had the full aperture on all the evening, the air was very
good, but not perfect. Alpha Lyræ was a splendid object with all
powers, a most brilliant disk with just indications of circular
rings—no wings or rays. I turned it on B Cygni, and the beauty of
the mirror stood revealed, both stars _perfect disks_, with _just_
the indication of perfect circular defraction rings, and the colours
were most beautiful,—nothing could possibly appear finer. I consider
the mirror perfect, and the stand most convenient and smooth and
pleasant in action.

                                                 I am, dear Sir,
                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. E. H. LOWE.

                                                 WILMCOTE,
                                                     _April, 1880_.

DEAR Mr. CALVER,—I have been exceedingly occupied, as there has been
a succession of gloriously fine nights, and I have secured the
Nebulæ diagrams I so much wished for Mr. WEBB,—and I would allow
nothing to divert me from them—but I put it (a 15-1/2 in.
equatorial) on Zeta Cancri, and it was shown beautifully. I have
been working at the driving clock, and it is under capital control.
The great cluster 13 M., is a glorious object, and magnificently
resolved. I see all I look for on the Moon.

                                                 Faithfully yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ W. SCOTT, Esq.

                                             SOUTHWICK, SUNDERLAND,
                                                      _July, 1880_.

DEAR SIR,—Dr. Blacklock, and also Mr. Bell, have seen the mirror,
and pronounce it perfect, and it performs admirably.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ JAMES L. MCCANCE, Esq., F.R.A.S.

                                          PUTNEY HILL, S.W.,
                                              _October 23rd, 1879_.

DEAR Mr. CALVER,—Weather and circumstances have been very
unfavourable for doing much work with the 10 inch reflector since I
got it from you. But with what I have seen with it I am very
pleased; in good weather the views of the planets, Jupiter and his
“Great Red Spot” especially, were grand. The mounting (equatorial)
is quite satisfactory, and the movements work smoothly and well.

                                                 Yours very truly,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ FRANK C. DENNETT, Esq.

                                 10, TERMINUS TERRACE, SOUTHAMPTON,
                                                 _July 11th, 1880_.

DEAR SIR,—It is a long time ago that you asked me to write and let
you know how I liked the 9-1/2 in. I have not done so because I
wished first to see what was to be made of the planets.

Last night, at 14^h 30^m, I had my first peep at Jupiter through it,
and a grand sight it was; his belts coloured, though not so vivid as
they are sometimes, were fine in the extreme; and, though the power
employed was only the achromatic 215, the satellites were beautiful
little discs, one especially showing the tint of its surface.

A quarter of an hour later Saturn was in the field of view; a grand
object, several of the satellites surrounding it. A little cloud was
coming up over it, so I could not see so much of this planet as I
should have liked, though amply sufficient to prove incontestably
its high class.

With double stars I have not attempted much, though on turning it on
μ^2 Boötis I found the division easy, the components being
respectively slightly orange, and dullish white or pale yellow.

I have had lots of grand views of the wonders of the “star depths,”
clusters, and nebulæ, notably 57 Messier, the Ring nebula, in Lyra,
the great Orion nebula, and the marvellous Whirlpool nebula, the
chief outlines of which were well shown.

Hitherto the instrument has been chiefly employed on the Moon, the
details of which come out hard and sharp in a beautiful manner, with
all powers up to 515, the highest I have.

The 5-1/4 in. pleased me very much, but the 9-1/2 in. delights me.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ G. W. ROYSTON PIGOTT, Esq., M.D., F.R.S., F.R.A.S., &c.

                                                 EASTBOURNE,
                                                      _July, 1880_.

DEAR SIR,—There has been but little weather for testing. Mr. Slack
has been staying with me; we are delighted with the 8-1/2″, and
think it a great beauty. I can hardly imagine any mirror much
better, and I expect great precision from it. I find its focus to be
65 inches, not quite so much as my fine Dollond glass, of 3-3/4 in.
aperture.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ A. WILLIAMS, Esq.

                          CLARENCE LODGE, GRAFTON STREET, BRIGHTON,
                                                    _August, 1880_.

DEAR SIR,—I had intended writing to you to express my pleasure in my
5-1/4 in. telescope nearly a month ago, but thought I would have
another look first, and the more I look the more I am pleased with
it. I cannot now imagine anyone preferring a 3-1/4 in. refractor to
one of these. I have had no trouble at all with the adjustments, and
if was to get out of adjustment, it could be rectified in about five
minutes. Notwithstanding the unsettled weather (giving on an average
only about one fine night in eight), I have examined nearly two
hundred double stars in the last three months, some of them very
difficult. I enclose a list of a few, which will show very well the
capabilities of the instrument.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.


      LIST OF OBJECTS SEEN WITH A 5-1/4 INCH REFLECTOR.

ξ Scorpii (5, 5·2 : 1″·3) clearly divided, 186 power.

ε Lyræ. Debilissima quite easy; 186, 380 powers, though nearly half
Moon.

μ^1 Herculis (9·4, 10 : 1″·04). Just divided, 380. Very difficult,
owing to its faintness.

Vega. 11 mag., comes quite plain, only 47 minutes before sunrise;
powers 110, 186.

φ Virginis (5, 13 : 4″·27). Comes plain, 110, 186.

ν Scorpii, the close pair (4, 5 : 0″·8), well elongated, power 380;
small star (7, 8 : 1″·68) divided, 110.

ζ Boötis (4, 5 : 0″·88) elongated 186, notched 380, and with field
lens removed, all but divided.

δ Cygni (3, 9 : 1″·63), 9 plain, 380 on several occasions.

Antares is chiefly an atmospheric test, but the companion was quite
plain on one occasion out of the three I looked for it.

μ^2 Boötis (7·5, 8 : 0″·63), considerably elongated, 380.

η Coronæ (5·5, 6 : 0″·62), slightly elongated, 380; but not nearly
so much as μ^2 Boötis.

56 Herculis (6·5, 13 : 15″), 13 easy, all powers.

π Aquilæ (6, 7 : 1″·5). Just separated, 110; 14 mag. (Webb), just
visible, 186.

ε Equulei. Just divided, 186 (5·7, 6·2 : 1″·0).

       *       *       *       *       *

      _From_ D. TRAILL, Esq.

                                             BALHAM,
                                                 _March 5th, 1880_.

MY DEAR SIR,—I have at present to use the telescope, an 8-1/2 in.
Alt Azimuth, out of a window, and so at a great disadvantage,—in
fact cannot give it a fair trial till I have the house ready for it,
meanwhile I use it as occasions offer, and have been highly pleased
with it. The views of the nebular in Orion resemble those of BOND’S
drawings, and shows immeasurably above my 3-1/4, of course. I think
the mirror is _perfect_ from its performance on large stars whose
disks are small and round, without rays of any kind. I am
_thoroughly_ satisfied.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ HUGH AULD, Esq.

                               GROSVENOR CRESCENT, EDINBURGH, 1879.

DEAR SIR,—I have not been able to do much with the telescope, a
5-1/4″ Angle-block, through the unfavourable weather for the last
four months, but with the opportunities I have had its performance
is satisfactory; it performs well on stars with high powers, and I
am sure it will bear a good deal higher. I am very well pleased with
the instrument.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. THOS. H. BROWNE, F.R.M.S., &c.

                                      THE CEDARS, HIGH WYCOMBE,
                                             _February 26th, 1880_.

DEAR SIR,—I am exceedingly pleased with the action of your mirror
(an 8-1/2 in. equatorial); what I have seen of sun, moon, planets,
and stars is splendid. I have had a good many telescopes, but never
liked one so well as the one you have sent me. For the first day or
two I could do nothing but admire it.

                                                       Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. CONYBEARE W. BRUCE, M.A., F.R.A.S.

                                    ST. NICHOLAS’ RECTORY, CARDIFF,
                                                 _July 17th, 1880_.

MY DEAR Mr. CALVER,—You will have been looking for some news of me
and the 12″. I have purposely delayed writing until I was _really_
in a position to say something definite, and you had already heard
my high opinion of the mirror. Let me at once say that that opinion
has been _more_ than justified. The mirror is a _beauty_. Canon
Beechey and I got Jupiter and Saturn at 2.30 a.m. yesterday
morning—and they were _superb_. The Canon declared enthusiastically,
that he “had _never_ seen Saturn anything like that,” and the last
thing he said to me on the subject as I parted with him to-day was,
“You have got a very fine instrument indeed.”

If I _could_ add anything more in its praise it would be this, that
I am really going to build a _new observatory_ for it—my present one
is too small and cramped.

                                                  Sincerely yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      (_Another Letter from the same Gentleman._)

                               ST. NICHOLAS’ RECTORY, NEAR CARDIFF,
                                               _August 28th, 1880_.

DEAR Mr. CALVER,—The 12 inch surpasses all my expectations. It has
the perfection in figure of the incomparable 10 inch of yours, which
was its immediate predecessor, and, in grasp of light, the
difference in favour of the 12 inch over the 10 inch, a most
brilliant mirror, is simply astounding.

You may equal the 12 inch—I am sure you will, whenever you make
one—but you will not easily beat it. Mr. SADLER, the well-known and
most accurate observer, has himself worked with it, and writes of it
to me as follows:—“The 12 in. is considerably superior in light
grasping power to H2’s 20 ft. reflector, and the figure is a much
finer one.”

Your skill and kindness has placed me in the front rank among
amateur observers, as far as the possession of optical means is
concerned.

I was afraid that the German Stand would not prove so convenient as
the “Berthon Equestrian Stand,” but I find it is and far more so.
The German Stand is, for anything above 6 in., decidedly more solid
and dependable, and far simpler in any case. The merit of the
“Berthon Equestrian” form is that it requires a smaller observatory.

                                             Very sincerely yours,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ W. S. FRANKS, Esq., F.R.A.S.

                                           LEICESTER,
                                               _August 19th, 1880_.

MY DEAR SIR,—As the 11-1/4 in. speculum has now been in constant use
for two years, I may be allowed to express my opinion, with all due
deliberation, as to its performance. It has been tried upon almost
every conceivable object during that period with uniformly good
results. Having also a 5 in. achromatic of the finest quality, I
have been enabled to make a great number of comparisons between the
two instruments, mounted side by side: and for fine definition,
smallness of star discs, and freedom from chromatism, the reflector
always came out victorious. Upon first mag. stars, nothing could
surpass the purity of the image in the reflector; but on immediately
turning to the achromatic, the outstanding violet rays were
painfully obtrusive. For red stars, which are generally small, the
reflector seems especially adapted. I used to be rather sceptical
about the tints of red stars, but must confess, after seeing the
magnificent tints of scarlet and crimson which are shown by a large
aperture, that my doubts have vanished. Definition upon the planets,
in good air, is simply perfect. The detail on Jupiter and Saturn
reminds one of an exquisite engraving. The far distant Neptune is
perfectly defined as a tiny disc, and his moon steadily visible with
the 11-1/4 in. The faculæ and other Solar detail are brought out
with wonderful distinctness. As for the Moon, the crispness of
definition, absence of colour, and immense number of minute objects
shown by the reflector, leave nothing to be desired. The gorgeous
views of clusters and nebulæ: the brilliantly crowded fields in the
galaxy: and the endless variety of star colours and groups are
almost beyond description, and must be seen to be appreciated. I
could fill pages about objects seen with the 11-1/4 in. mirror, but
will not occupy more space, save to thank you for having placed such
perfect instruments within the reach of amateurs.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ W. S. FRANKS, Esq., F.R.A.S.

                                             LEICESTER,
                                                 _September, 1878_.

MY DEAR SIR,—Mr. BURNHAM is undoubtedly “facile princeps,” as an
observer of double stars. Few men could have discovered such
difficult objects as he has done with a 6″ O.G. Perhaps, it ought to
be conceded that the usual formula for separating power, requires
modification in his case, as Pogson’s formula for “minima visible”
did with Mr. J. W. WARD, of Belfast. Apropos of this topic: do you
recollect Mr. WARD’S discovery of several additional comites to Pxx
452 Cygni? One of them Mr. BURNHAM only succeeded in seeing with the
greatest difficulty with the 6″ O.G. when the large star was hidden
by a bar. I can see this easily enough with the 11-1/4 in. mirror,
in presence of the brighter star.

When you have any intending customers halting between two opinions,
or in any way dubious about reflectors—if you will refer them to me,
I shall have great pleasure in giving my testimony. Reflectors have
been very badly used, and in justice to them I shall not hesitate to
express my honest conviction whenever it is asked.

                                                  Yours sincerely,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ PHILIP VALLANCE, Esq.

                                           COBB COURT,
                                               _August 24th, 1880_.

DEAR Mr. CALVER,—I write to thank you for the very excellent 12 in.
mirror you have worked for me. You know that I have excellent
opportunities of testing it by those of With, Bird, Grubb, Murrell,
and others; and also for definition by a capital 6 in. refractor—and
I can truly say it is surpassed by none, and equalled by few: it is
quite my favourite instrument, and has been a source of much
enjoyment ever since I have had it, and again I thank you for
working me such a treasure.

                                    I am, dear Mr. Calver,
                                                 Yours very truly,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ THE REV. N. S. GODFREY, F.R.A.S.

                              ST. BARTHOLOMEW’S VICARAGE, SOUTHSEA,
                                               _August 23rd, 1879_.

MY DEAR Mr. CALVER,—The 12 inch mirror which you worked and mounted
for me gives me perfect satisfaction. I think I have had sufficient
experience with telescopes to justify the expression of a confident
opinion, as at one time or other I think I have had 13 achromatic
telescopes by Tulley, Dollond, Simms, Jones, Cooke, and Murrell, of
apertures varying from 2-1/4 to 7 inches, besides 5 graduated
instruments. The one I had before yours was an 8-1/8 With-Browning,
which With himself considered of as fine a figure as he could work,
and it certainly was a beautiful mirror. Your 12 inch is quite as
perfect in its definition. I have soon on particularly fine evenings
Castor as two discs, without wing or ray. I have separated with ease
ω Leonis, μ^2 Boötis, η Coronæ, γ^2 Andromedæ, and many others of
that class. The planets Jupiter and Saturn on fine nights are
magnificent. I could go into more detail, but I think the facts I
have mentioned are sufficient to convey an idea of the performance
of the mirror; and I am particular in expressing my opinion thus
strongly, because great names, with no experience of reflectors, are
committed to their condemnation. I am certain that under favourable
circumstances they are _quite_ equal in their performances to
refractors. I know my 8-1/8 With was in every way equal to my 7 inch
Troughton and Simms, and in light superior, when newly silvered. And
when the cost is taken into consideration, Cooke’s price of a 10
inch O.G. being £390, without mounting, and your price for a 10 inch
mirror being only £25, I can only express my astonishment that there
can exist any doubt in the scientific mind upon the subject.

May I say that I shall be pleased to answer any questions that any
of your intending purchasers may wish to ask. I cannot speak too
highly of your mirror. I may add that through the courtesy of its
possessor, A. A. COMMON, Esq., I saw Jupiter magnificently last year
in the 37″ mirror you worked for him.

                                     I am, my dear Mr. Calver,
                                                 Very truly yours,
                                                        (_Signed_.)

       *       *       *       *       *

      _From_ THE REV. CANON ST. VINCENT BEECHEY, F.B.A.S., &c.

                                  HILGAY RECTORY, DOWNHAM, NORFOLK,
                                                 _June 22nd, 1880_.

MY DEAR CALVER,—I really do not know how to thank you enough for all
the pleasure you have given me, and for the excellence of the work
you have done for me. I like it more and more! It is really as near
perfection as I could ever hope for. Even at my old age of nearly
eighty, I divide 1 second stars like two dots, and I used a power of
700 on my 8 foot. What mirror but of great excellence would bear
that power, and give you two _dots_! I would not part with it for
anything. When I have been to Mr. Bruce he is coming to me, and we
will try your 12″ against my 10″. He will have light, a great thing
for me, but I do think he _cannot_ have _better_ definition. I hope
nothing will prevent his getting the 12″ in time for us to adjust
and try it. My telescope, now complete, is a gem, and has given me
more pleasure than any other scientific thing.

                                        Ever most sincerely yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ THE REV. J. GWYNNE HUGHES, F.M.S., &c.

                                           MALDON,
                                               _August 30th, 1880_.

MY DEAR SIR,—All my friends are greatly pleased with the 10 in.
reflector you have made me—with its general appearance and superior
workmanship.

The wheel at the foot adds very much to its portability. Tho form of
its stand is the best I have seen, giving a complete sweep without
any fresh adjustment. The cell bearing the reflector drops into its
place without any difficulty, even in the dark. The trials I have
made of the instrument have revealed a clearness and sharpness of
definition far superior to anything of the kind I had seen before.

I am indebted to you for a source of boundless scientific interest
at very moderate expense. With best wishes,

                                       I remain, dear Sir,
                                                  Yours sincerely,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ WALTER GOODACRE, Esq.

                                                SEVEN SISTERS ROAD,
                                                       _May, 1879_.

DEAR SIR,—Respecting the 5-1/4 in., I am very much pleased with it;
the definition is very good.

As a proof of the excellence of the mirror, I may mention that I
have on several occasions seen the small crater on the floor of
Helicon, given by WEBB as a test for a 9 in. mirror.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

      (_Another Letter from the same Gentleman._)

       *       *       *       *       *

      _From_ REV. N. S. GODFREY, F.R.A.S.

                                               _October 4th, 1880_.

DEAR SIR,—I have been able to get to use my telescope again, and
send you some of my seeings.

_June 17th._—α Herculis. Still night, 10 p.m., light haze. Discs
beautifully small. Occasionally without any interference ring.

_July 18th._—ζ Herculis. Beautifully seen, power 496, Cooke.

_August 16th._—Well seen. 6.15 p.m., daylight.

_August 26th._—σ Cygni. Misty. Adjustment beautiful. Small star well
seen. ψ Cassiopeæ. Double blue star well divided.

_August 27th._—ζ Herculis. Both stars occasionally without ray or
ring. Two brilliant dots. Colour of companion, pale lilac. Full
aperture. Power 207, Cooke. 6 p.m.

_August 30th._—Dumb bell nebula. Well seen. Not at all regular in
outline, as given by H. Several glimpse stars.

_September 24th._—ζ Herculis. Very fine definition. The difficulty
with this star is clearly atmospheric. I saw it well with 8 in.
aperture, power 207: but the interference ring became thicker and
continuous all round: probably owing to the larger size of my
diagonal prism, nearly 2-1/2 in.

The planets are now again simply magnificent. All the usual details
I see splendidly with full aperture of 12 in., and as sharp as if
cut out with a penknife. The great red spot is a wonderful
phenomenon. What is it?

The great nebula in Andromeda, seen through your fine nebula power
is a mysterious sight. You seem to be looking at something which
eludes your vision (except the nucleus); you see it, and yet,
ghost-like, you see through it. I long for the great nebula in
Orion. I did not see it last year on account of illness.

                                  Believe me,
                                        My dear Mr. Calver,
                                                 Very truly yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ T. HILDERSLEY, Esq.

                                       33, BERWICK STREET, W.,
                                             _September 9th, 1880_.

DEAR SIR,—I am very pleased to be able to tell you that I have got
the 8-1/2 in. mirror into very fair adjustment—only a slight flare
on one side, which I could correct if clouds had not come up, and I
have not had a chance since, as my time is very limited.

As it was, comes to Wega came out fine; also debilissima, ε Boötis,
μ^2 Boötis, was well seen. Stops made little improvement.
Nebula in Andromeda very fine, both large and small. Clusters in
Hercules well resolved, and Jupiter and Saturn, though low down,
were grand; all is clear with any power or aperture.

                                                      Yours truly,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ REV. E. A. FISHBOURNE, M.A.

                                         MINOR CANONRIES, LLANDAFF,
                                               _October 4th, 1880_.

MY DEAR SIR,—I send you my cheque, which I do with the greatest
pleasure. I am delighted with, the telescope and with its
capabilities.


                                                  Faithfully yours,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ WALTER GOODACRE, Esq.

                                                        LONDON, N.,
                                             _September 6th, 1880_.

MY DEAR SIR,—The 8-1/2 in. mirror which you supplied me with during
the early part of the year, I have recently mounted as a simple
equatorial. And although I have had but few opportunities at present
of using the same, they have been sufficiently numerous to prove,
beyond doubt, the great excellence of the mirror.

On the evening of the 3rd September, I had some beautiful views of
Jupiter and Saturn. In the former the deep coppery hue of the
equatorial belts, and of the large spot, at present visible on his
southern hemisphere, were strikingly conspicuous, as were many
minute details of his surface. In the case of Saturn, the gradations
of light on the rings, and the delicately tinted belts on the planet
itself, also the sharply defined shadow of the planet on the rings
were easily seen.

Its definition of the most minute portions of the moon’s surface,
leaves nothing to be desired, whilst its performance on double stars
is equally satisfactory.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ G. W. ROYSTON PIGOTT, Esq., M.D., F.R.S., F.R.A.S., &c.

                                          EASTBOURNE,
                                               _October 4th, 1880_.

DEAR SIR,—Your figuring of the 8-1/2 in. mirror has given me much
satisfaction. I see ε^1 ε^2 Lyræ, and such stars, with 600, very
sharp and clear.

I have counted six satellites of Saturn, and the equatorial belt is
very distinct.

Last week I happened to observe Jupiter, when a black shadow of a
satellite was beautifully notching the limb, at the same time a
small pearl-like satellite was about to egress from the belts. I
saw, also, six spherical cloudlets on the belts.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      _From_ REV. S. MILLS, M.A.

                                        DROYLSDEN,
                                             _September 4th, 1880_.

DEAR Mr. CALVER,—To-night was an exceptional fine night for the
stars, the like of which I have not had since I got your 6-1/2 in. I
had for a week or so been observing with my home-made 8 in., but
to-night again recurred to _yours_, and its _superiority_ was all
the more _conspicuous_ and _gratifying_. It quite _delighted me
afresh_!

Looking at β Cygni, I picked up two, to me, new stars, which I think
fully completes Mr. SADLER’S tests in this field. I mark the newly
found ones in red. This only shows that one has only patiently to
watch and wait for a suitable observing night to get one out of a
certain aperture it is capable of showing.

The vast superiority of your 6-1/2 in. _has quite put my 8 inch out
of court_!!

                                                  Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      (_From the same Gentleman._)

                                     DROYLSDEN RECTORY, MANCHESTER,
                                                 _July 30th, 1880_.

MY DEAR SIR,—I can scarcely express to you the pleasure I have had
in the use of your splendid 6-1/2 in. mirror. Both in light grasping
power, and in the separation of close double stars, it has far
surpassed my highest expectations, and quite removed the prejudice I
entertained against reflectors. Though possessing a first-class
4-1/4 in. refractor, equatorially mounted in my observatory, I now
use your mirror in preference, in the more difficult and delicate
observations, and with it am able to master the most severe tests
given for 6-1/2 in. aperture. I would not be without one of your
finely figured mirrors, now that I have tested their merits, for any
consideration.

                                                        (_Signed_.)
Mr. G. CALVER.

       *       *       *       *       *

      (_From the same Gentleman._)


                                          THE RECTORY, DROYLSDEN,
                                               _October 4th, 1880_.

MY DEAR SIR,—I have given your 8-1/2 in. mirror one night’s trial,
and it has greatly pleased me. Its resolution of the great cluster
in Hercules was truly magnificent, and the clearness with which it
brought out stars very difficult with 6-1/2 in. was highly
gratifying. I hope to turn it to very good account.

                                                 Yours faithfully,
                                                        (_Signed_.)
Mr. G. CALVER.


 [ Illustration: (FIG. 1.) ]


 [ Illustration: (FIG. 2.) ]


 [ Illustration: (FIG. 3.) ]


      Printers: WARREN HALL & LOVITT, 88, Camden Road, London. N.W.


TRANSCRIBER’s NOTE:
The constelation Boötis also appears in the original spelt as Bootis
and Böotis these have all been corrected to Boötis without being
noted below. Also variations in hyphenation remain unchanged.

The following typos are corrected in this e-text and are shown within
the text as

            Original                       Replaced by
 Page 4     Many of the speculas           Many of the specula
 Page 7     on the pitch                   or the pitch
 Page 24    and proceed                    and proceed.
 Page 28    kept is glass                  kept in glass
 Page 31    See p. 27, Fig. 4              See p. 20, Fig. 4
 Page 39   (prices for 8-1/2 then 6-1/2)  (prices for 6-1/2 then 8-1/2)
 (appendix)
 Page 14    Rev. W. P. MATTHEWS            REV. W. P. MATTHEWS
 Page 24   (a 10 in. Alt Azimuth.         (a 10 in. Alt Azimuth).
 Page 32    Rev. E. A. FISHBOURNE, M.A.    REV. E. A. FISHBOURNE, M.A.





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