APPENDIXTOHints on Silvered Glass Reflecting Telescopes.
drop cap letter T
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 theoriginal 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, andeverythingused 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 thesametemperatureas 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 theequaltemperature 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; thenunscrewthe side screw. If the spot is nearer the other edge of flat,screw it uplittle 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 tohold, 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 onface of flatare 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 instrongsunlight 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 theircompleteefficiency, 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 perfectto 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 itused to be accepted as an incontrovertible fact that an aperture of G inches was the largest that could be used onaveragenights 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 theextreme edgeby 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.
CATALOGUEOFSilvered Glass Reflecting Telescopes, &c.,AND THEIR ACCESSORIES,OCTOBER, 1880.
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 thebest 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 byG. 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 shownin 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.
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
17, 18, to 20 inch Speculum, with 10 powers, from 50 to 800, including Kellners, Huyghenians, and Achromatics,
22 to 24 inch Speculum
30 inch Speculum, with 12 powers and position micrometer, and transit eye-pieces
Prices will be forwarded for special arrangements in any of these large sizes.
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 mostexcellent 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.
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
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
8-1/2 inch Speculum, as above, with 10 inch circles, 4 powers
10 inch Speculum, as above, with 10 inch circles, 5 powers
12-1/2 inch Speculum, as above, with 10 inch circles, 5 powers
TheEducational Reflectoris 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.
ThePopular Reflector(Fig 3), with Angle-Block stand, with endless screw-motion to follow the stars with equatorial motion.
These are also made with rotating body.
Reflecting Telescope onAlt-azimuth Stand, fitted with silvered glass Speculum, and provided with two eye-pieces.
Silvered-Glass Specula (unmounted).
THE FINEST QUALITY GUARANTEED.
Silvered-Glass Diagonal Mirrors (unmounted).
FINEST QUALITY GUARANTEED.
Silvering and Polishing Specula.
ASTRONOMICAL EYE-PIECES.
OF BEST QUALITY.
Huyghenian Constructionof the following magnifying powers on a 6-1/2 feet focus object-glass:—
Good Instruments will be taken in exchange, and liberally allowed for.
GEORGE CALVER,
HILL HOUSE, WIDFORD,
CHELMSFORD, ESSEX.
FromW. 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.
FromF. 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.)
FromD. 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.
FromW. 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 doalone(in my opinion) well repay the cost of the telescope.
Yours truly,
(Signed.)
Mr.G. Calver.
FromA. 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 avery finemirror.”
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 avery finemirror.”
(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.
FromJ. 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.
FromTheRev.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, γ2Andromedæ 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.
FromH. 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.
πAquilæ.—Divided, power 80. 14-m.Webb might have been rated 15-m.[6-m.,7-m.1″·5.]
δAquilæ.—[a3-1/2,b16,c14,a-b96″,a-c194″.] Comites easy, 3 other excessively minute ones, not shown by the 11 inch refractor with which P. Smyth measuredB.C.Found 6-1/2 in. Sept. 12th, est. ± 17 mag. 100″ to 110″.
ζPersei.—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.
βDelphini.—Close double discovered by Burnham, est. 0″·7. In contact 6-1/2 in., power 430.
ηCoronæ Borealis.—Very low, long past meridian, in contact 164 power.
βEqualei.—[a5-1/2,b13,c14,n16:a-b35″,a-c50″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?)
μAndromedæ.—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.
P.178 xx.Delphini.—[a7-1/2,b8,c16,b9:a-b14″·3,b-b0″.7,a-c20″.] Smyth 16 by evanescent glimpses; easy 164 power, 6-1/2 in. 8-m.well elongated in direction of 230°, power 430.
FromH. 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.)
FromT. 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.)
FromThe 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.
FromJ. 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.