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stone and printed without any intermediate operation. The Messrs. Browning exhibited a silvered glass reflector, equatorially mounted in a very handy form on the Frauenhofer plan. Probably the most important thing shown was Mr. Cooke's gigantic object-glass, constructed for Mr. Newall, of Gateshead. The clear aperture is 25 inches, and therefore it can lay claim to being the largest object-glass in existence. The Astronomer Royal sent a model in wood of the Greenwich transit instrument, showing the aperture that has been pierced in the axis in order that the north and south collimators may be observed through it. Mr. Balfour Stewart sent from the Kew Observatory an apparatus used for showing the heating of a metallic disc by rotation, in vacuo, devised by Mr. Beckley. Regrets were expressed that the character and design of this instrument were not fully set forth on the description card appended to it. To enumerate the miscellaneous objects displayed on the tables would be to reprint an optician's catalogue; suffice it then to say that microscopes, telescopes, transit instruments, theodolites, stereoscopes, spectroscopes, &c. &c., without end, were exhibited by all our leading instrument makers-Smith & Beck, Browning, Cooke, Ladd, Powell & Lealand, Troughton & Simms, Elliott, and others. Amongst the company we noticed Sir E. Belcher, Sir R. Murchison; Professors Tyndall, Wheatstone, Miller, and Rymer Jones ; Admiral Manners, Capt. Noble; the Revs. C. Pritchard, F. Howlett, R. Main, Godfrey, Sargent; Messrs. Glaisher, Huggins, Dunkin, Nasmyth, Brayley, Perigal, Hopkins, Buckingham, Newall, Whitbread, Lockyer, Burr, Simms, Hind, Lynn, Stone, Cooke, Du Chaillu, Hodgson, Gorton, Grove, Q.C., Chambers, W. Spottiswoode, Casella, Kincaid, Cummings, Williams; Archbishop Manning; Drs. Bence Jones, Webster, &c. &c., accompanied in many cases by their ladies.

CELESTIAL PHOTOGRAPHY.*

By A. BROTHERS, F.R.A.S.

THE credit of having produced the first photograph of a celestial object is generally given to the late Mr. Bond, of Cambridge, U.S.; but it appears from a paper by Professor H. Draper, of New York, published in April 1864, that in the year 1840 his father, Dr. J. W. Draper, was the first who succeeded in photographing the moon. Dr. Draper states that at the time named (1840), "it was generally supposed the moon's light contained no actinic rays, and was entirely without effect on the sensitive silver compounds used in Daguerreotyping." .With a telescope of 5 inches aperture Dr. Draper obtained pictures on silver plates, and presented them to the Lyceum of Natural History of New York. Daguerre is stated to have made an unsuccessful attempt to photograph the moon, but I have been unable to ascertain when this experiment was made.

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Read at a meeting of the Photographic Section of the Literary and Philosophical Society of Manchester, December 14, 1865.

Mr. Bond's photographs of the moon were made in 1850. The telescope used by him was the Cambridge (U.S.) refractor of fifteen inches aperture, which gave an image of the moon at the focus of the object glass two inches in diameter. Daguerreotypes and pictures on glass mounted for the stereoscope were thus obtained, and some of them were shown at the Great Exhibition of 1851, in London. Mr. Bond also proved the advantage to be derived from photographs of double stars, and found that their distances could be measured on the plate with results agreeing well with those obtained by direct measurement with the micrometer.

Between the years 1850 and 1857 we find the names of Father Secchi in Rome, and MM. Berch and Arnauld in France, and in England Professor Phillips, Mr. Hartnup, Mr. Crookes, Mr. De la Rue, Mr. Fry, and Mr, Huggins. To these may be added the name of Mr. Dancer, of Manchester, who in February 1852 made some negatives of the moon with a four and a-quarter inch object glass. They were small, but of such excellence that they would bear examination under the microscope with a three-inch objective, and they are believed to be the first ever taken in this country. Mr. Baxendell and Mr. Williamson, also of Manchester, were engaged about the same time in producing photographs of the moon.

The first detailed account of experiments in celestial photography which I have met with is by Professor Phillips, who read a paper on the subject at the meeting of the British Association at Hull in 1853. Professor Phillips says, "If photography can ever succeed in portraying as much of the moon as the eye can see and discriminate, we shall be able to leave to future times monuments by which the secular changes of the moon's physical aspect may be determined. And if this be impracticable—if the utmost success of the photographer should only produce a picture of the larger features of the moon, this will be a gift of the highest value, since it will be a basis, an accurate and practical foundation of the minuter details, which, with such aid, the artist may confidently sketch." The pictures of the moon taken by Professor Phillips were made with a six and a-quarter inch refractor, by Cooke. It is of eleven feet focus, and produces a negative of one and a-quarter inches diameter in thirty seconds. Professor Phillips does not enter very minutely into the photographic part of the subject, but he gives some very useful details of calculations as to what may be expected to be seen in photographs taken with such a splendid instrument as that of Lord Rosse. It is assumed that an image of the moon may be obtained direct of twelve inches diameter, and this when again magnified sufficiently would show "black bands twelve yards across." What may be done remains to be seen, but up to the present time the Professor's anticipations have not been realised.

We have next, from the pen of Mr. Crookes, a paper communicated to the Royal Society of London, in December 1856, but which was not read before that society until February in the following year. Mr. Crookes appears to have obtained good results as early as 1855, and, assisted by a grant from the Donation Fund of the Royal Society, he was enabled to give attention to the subject during the greater part of the year following. The details of the process employed are given with much minuteness. The telescope used was the equatorial refractor at the Liverpool Observatory, of eight inches aperture, and twelve and a-half feet focal length, producing an image of the moon 1.35 inch diameter. The body of a small camera was fixed in the place of the eyepiece, so that the image of the moon was received in the usual way on the ground glass. The chemical focus of the object glass was found to be eight-tenths of an inch beyond the optical focus, being over-corrected for the actinic rays. Although a good clock movement, driven by water power, is applied to the telescope, it was found nɛcessary to follow the moon's

motions by means of the slow-motion handles attached to the right ascension and declination circles, and this was effected by using an eye-piece, with a power of 200 on the finder, keeping the cross-wires steadily on one spot. With this instrument Mr. Hartnup had taken a large number of negatives, but owing to the long exposure required he was not successful; but with more suitable collodion and chemical solutions, and although the temperature of the Observatory was below the freezing point, Mr. Crookes obtained dense negatives in about four seconds. Mr. Crookes afterwards enlarged his negatives twenty diameters, and he expresses his opinion that the magnifying should be conducted simultaneously with the photography by having a proper arrangement of lenses, so as to throw an enlarged image of the moon at once on the collodion plate; and he states that the want of light could be no objection, as an exposure of from two to ten minutes would not be "too severe a tax upon a steady and skilful hand and eye."

In an appendix to his paper Mr. Crookes gives some particulars as to the time required to obtain negatives of the moon with different telescopes, from which it appears that the time varied from six minutes to six seconds. The different results named must, I conclude, have been caused not so much by the differences in the instruments as in the various processes employed, and in the manipulation. I must observe, also, that it is not stated whether all the experiments were tried upon the full moon, a point materially affecting the time.

Mr. Grubb read a paper on this subject before the Dublin Photographic Society on May 6, 157. After referring to the fact that he found the actinic focus of his object glass to be longer than the visual (thus agreeing with Mr. Crookes), he states it to be generally understood that in a compound object glass made as nearly achromatic as possible, the actinic focus is shorter than the visual. The most valuable portion of Mr. Grubb's paper is the suggestion for a piece of apparatus to be attached to the part connected with the telescope for holding the dark frame, which he proposes may be so arranged as to follow the moon's motion in declination; and he gives the following description of a contrivance used by Lord Rosse, and which is suitable for telescopes not equatorially mounted :—"On a flat surface attached to the telescope, and parallel to the plane of the image, is attached a sliding plate, the slide being capable of adjustment to the direction of the moon's path at the time of operating. The slide is actuated by a screw moved by clockwork, and having a governor or regulator of peculiar construction, which acts equally well in all positions. The clockwork being once adjusted requires no change; but the inclination of the slide must be effected by trial for the moon's path at the time of taking the photograph." This idea originated with Mr. De la Rue; Lord Rosse's share in it arose from his having applied a clock motion to the apparatus. The telescope used by Mr. Grubb is 12 inches aperture and twenty feet focus, giving an image 21 inches diameter, in from ten to forty seconds. The next contribution on this subject is by Mr. Fry, who, in 1857, commenced his experiments on the moon with an equatorial telescope, the property of Mr. Howell, of Brighton. The object glass of this instrument is eight and a-half inches diameter and eleven feet focus, and gave an image of the full moon in about three seconds, but under very favourable circumstances a negative was made in a single second. The size of the image is not stated, but it must have been about one and a quarter inches diameter. Mr. Fry appears to have removed the eye-piece of the telescope, and in its place a board was fixed having a screw adjustment, so that a plate-holder could be moved backwards and forwards on the board (graduated to tenths of an inch) for the purpose of finding the actinic focus, which was three-quarters of an inch beyond the visual. He found that

this position of the chemical focus was variable, owing, as he thought, to the varying distance of the moon from the earth, but, as suggested by Mr. De la Rue, it might arise from the length of the telescope tube having altered through change of temperature.

In 1858 Mr. De la Rue read an important paper before the Royal Astronomical Society, from which it appears that the light of the moon is from two to three times brighter than Jupiter, while its actinic power is only as six to five, or six to four. On December 7, 1857, Jupiter was photographed in five seconds and Saturn in one minute, and on another occasion the moon and Saturn were photographed just after an occultation of the planet in fifteen seconds.

The report of the Council of the Royal Astronomical Society for 1858 contains the following remarks:-"A very curious result, since to some extent confirmed by Professor Secchi, has been pointed out by Mr. De la Rue, namely, that those portions of the moon's surface which are illuminated by a very oblique ray from the sun possess so little photogenic power that, although to the eye they appear as bright as other portions of the moon illuminated by a more direct ray, the latter will produce the effect called by photographers solarisation, before the former (the obliquelyilluminated portions) can produce the faintest image." And the report also suggests that the moon may have a comparatively dense atmosphere, and that there may be vegetation on those parts called seas.

At the meeting of the British Association at Aberdeen, in 1859, Mr. De la Rue read a very valuable paper on Celestial Photography. An abstract of this paper was published at the time in the British Journal of Photography, and in August and September of the following year further details of Mr. De la Rue's method of working were given in the same Journal. The processes and machinery employed are so minutely described that it is unnecessary here to say more than that Mr. De la Rue commenced his experiments about the end of 1852, and that he used a reflecting telescope of his own manufacture of thirteen inches aperture and ten feet focal length, which gives a negative of the moon averaging about 1 of an inch in diameter. The photographs were at first taken at the side of the tube after the image had been twice reflected. This was afterwards altered so as to allow the image to pass direct to the collodion plate, but the advantage gained by this method was not so satisfactory as was expected. In taking pictures at the side of the tube, a small camera box was fixed in the place of the eye-piece, and at the back a small compound microscope was attached, so that the edge of a broad wire was always kept in contact with one of the craters on the moon's surface, the image being seen through the collodion film at the same time with the wire in the focus of the microscope. This ingenious contrivance in the absence of a driving clock was found to be very effectual, and some very sharp and beautiful negatives were thus obtained. Mr. De la Rue afterwards applied a clockwork motion to the telescope, and his negatives taken with the same instrument are as yet the best ever obtained in this country.

The advantage of the reflecting over the refracting telescope is very great, owing to the coincidence of the visual and actinic foci, but it will presently appear that the refractor can be made to equal if not excel the work of the reflector.

Mr. De la Rue's paper (as published in the report of the British Association) contains some extremely interesting particulars as to the mode of obtaining stereoscopic pictures of the moon, and diagrams are given showing the effects of the moon's libration. The most beautiful stereoscopic prints of the moon are those by Mr. De la Rue. Mr. Fry also was very successful in this branch of celestial photography.

In this brief history of the subject of celestial photography, I have not referred to anything which has been done in making photographs of the solar spots, but the matter must not be altogether passed over. The first step in this direction appears to have been taken in France in 1845, by MM. Fizeau and Foucault, but it is chiefly due to the efforts of Mr. De la Rue that so much useful work has been done in heliography. In 1860 Mr. De la Rue and his staff of assistants performed one of the greatest feats yet recorded in this branch of the art of photography, having succeeded in obtaining several beautiful negatives of the various phenomena seen only during total eclipses of the sun, and two negatives were obtained during the totality. One question of much interest to astronomers was determined by this great experiment. The red prominences or flames generally seen as issuing from the edge of the moon were proved to belong to the sun. Photographs of the sun are taken daily when the weather is favourable at the Kew Observatory, and also by Professor Selwyn, at Ely. With the Kew photoheliograph pictures of the sun, spots have been made on the scale of the sun's diameter of three feet. Much, however, remains to be done. The light of the sun is so much in excess of what is required to obtain a collodion picture, that the loss of light consequent on the necessary interposition of lenses and the distance of the plate from the instrument can be no objection; and for these reasons I have very little doubt that, with apparatus suitably arranged, photographs of spots and groups of spots will be obtained of very much larger diameter than any yet taken.

The Quarterly Journal of Science for April 1864 contains the next important paper on Celestial Photography. It is by Dr. Henry Draper, one of the Professors at the New York University. On his return to America after paying a visit to Parsonstown, where he had the advantage not only of making some observations with Lord Rosse's large reflector, but also of seeing the method there pursued in grinding and polishing mirrors, stimulated by what he had seen, it was determined to build an Observatory, and to construct an instrument to be devoted solely to celestial photography. The speculum used by Dr. Draper is fifteen and a half inches in diameter, and twelve and a half feet focal length; but this was afterwards superseded by one of glass on Foucault's principle. The great labour involved in a work of this character may be judged of by the fact that Dr. Draper ground and polished more than 100 mirrors, varying in diameter from nineteen inches to a quarter of an inch; but he appears at last to have secured a good instrument. The chief points to be noticed in this article are, that instead of driving the telescope in the usual way by means of a clock, the frame carrying the glass plate was made to move on the plan previously referred to. Instead of clockwork to effect this motion, an instrument called a "clepsydra" was used. It has a weight on a piston rod, which fits into the cylinder filled with water, which is allowed to escape by means of a stopcock, and can be regulated with great exactness, so as to follow the object. The large number of 1,500 negatives are stated to have been taken at this Observatory, some of which would bear magnifying twenty-five diameters (the paper says times, but I assume this to be an error, as a negative must be very bad if it will not bear more than five diameters, or twenty-five times). As the average size of the negatives was 14 inch, an increase of twenty-five diameters would give an image of the moon nearly three feet in diameter. I have not seen the prints from these negatives, and have never heard anything of the quality of the work produced by this telescope; but it may be stated that Dr. Draper writes as if the negatives were of the best quality, and encourages others to follow his example.

(To be continued.)

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