October 9, 1890] 



NATURE 



569 



outline of the object it portrayed {Comptes rendus, vol. 

 XXX. p. 710, 1850). 



After the discovery of the collodion process by 

 Scott Archer in 1851, lunar photography grew apace. 

 Warren De La Rue exhibited some photographs of the 

 moon at the Royal Astronomical Society in 1853. With 

 respect to these pictures he afterwards remarked : " At 

 the latter end of 1852 I made some very successful positive 

 lunar photographs in from two to thirty seconds on a 

 collodion film, by means of an equatorially mounted 

 reflecting telescope of 13 inches aperture, and 10 feet 

 focal length, made in my workshop, the optical portion 

 with my own hands, and I believe I was the first to use 

 the then recently discovered collodion in celestial photo- 

 graphy." No automatic driving motion was attached to 

 the telescope, and the moon's motions both in right ascen- 

 sion and declination were followed by adjusting a sliding 

 frame attached to the eyepiece holder, in the diagonal 

 parallel with the moon's apparent path (Brit. Assoc. 

 Rep., Aberdeen, 1859, p. 131). 



In July 1853, Prof. J, Phillips obtained photographs of 

 the moon i^ inch in diameter on a collodion plate ex- 

 posed for five minutes in the first focus of a 6i-inch 

 refractor. .Some of the pictures were exhibited at the 

 Hull meeting of the British Association in September 



1853, on which occasion Prof. Phillips read a paper " On 

 Photographs of the Moon," and pointed out the many 

 advantages to be gained by the development of lunar 

 photography (Brit. Assoc. Rep., Hull, 1853, p. 14). He 

 also dwelt on the desirability of using reflecting tele- 

 scopes for the purpose because of the fact that in such 

 instruments the chemical and optical foci coincide. 



The Rev. J. B. Reade, the discoverer of many im- 

 portant improvements in photographic processes, made 

 several not very successful attempts to obtain daguerreo- 

 types, whilst Bond and Whipple were producing such 

 pictures in America. Later, in 1854, by exposing a 

 collodion plate for thirty-five seconds in the focus of a 

 reflector having an aperture of 24 inches, a negative of 

 the full moon was obtained from which enlargements 

 9 inches in diameter were made. These results were 

 exhibited at the meeting of the British Association held at 

 Liverpool in 1854 (British Association Report, 1854, p. 10). 



Mr. Hartnup, of the Liverpool Observatory, in con- 

 junction with Dr. Edwards and Mr. Forrest, also took 

 some lunar photographs in 1854, by means of an 8-inch 

 refractor, and exhibited the results at the above meeting 

 {ibid., p. 66). 



Prof. Crookes began work with the same instrument in 



1854, and his first step towards obtaining good negatives 

 was the introduction of the purest chemicals. This, and 

 a strict adherence to correct formulas, enabled him to 

 reduce the exposure from thirty to four seconds. The 

 diameter of the moon's image in the first foois of the 

 instrument used was v^$ inch, and the negatives ob- 

 tained bore an enlargement of twenty times, but on 

 account of the proportional magnification of defects in 

 the film, the results were not perfect. To eliminate 

 defects arising from this cause, Prof. Crookes suggested 

 that " The magnifying must be conducted simultaneously 

 with the photographing, either by having the eyepiece on 

 the telescope, or, better still, by having a proper arrange- 

 ment of lenses to throw a magnified moon image at once 

 on the collodion" (Roy. Soc. Proc, vol. viii. p. 363, 1857). 



In 1857, Mr. S. Fry obtained photographs of the full 

 moon by means of an eight and a half inch refractor. 

 With this instrument it was found that the average ex- 

 posure for the full moon was three seconds, for half moon 

 twelve seconds, and for quarter moon forty-five seconds ; 

 collodion plates being used. Mr. Fry observed that the 

 distance of the chemical focus from the object-glass was 

 subject to variation, the change being most probably due 

 to variations in temperature {Photographic Journal, vii. 

 p. 80, 1862). 



NO. 1093, VOL. 42] 



Secchi paid much attention to the photography of 

 particular portions of our satellite, and during the first 

 quarter. The chemical activity of the light of the moon 

 at full and at first quarter was found to be in the pro- 

 portion of three to one {Comptes rendus, vols, xlii., 

 I xlvi., 1856, 1858). In 1857, Sir Howard Grubb, using a 

 ! refractor of 12 inches aperture, obtained photographic 

 j images of the moon a little over two inches in diameter 

 [ with exposures from ten to forty seconds. A sliding back 

 similar to that invented by De La Rue and afterwards 

 I improved upon by Lord Rosse, was used to follow the 

 moon's motion. The improvement consisted in the 

 application of clock-work motion to the slide in order 

 j to follow motion in declination and in regulating the 

 driving clock of the equatorial to follow the moon in right 

 ascension (Dublin Photographic Society, May 6, 1857.) 



Although De La Rue obtained some excellent photo- 

 graphs in 1852, when working under very disadvan- 

 tageous conditions, it was not until 1857 that he began 

 to produce those detailed representations of the lunar 

 surface that have made his name immortal. The want 

 of a driving clock was the cause of the cessation of 

 lunar photography in the former year, and when this 

 had been supplied, De La Rue continued his work. 

 Numerous positives on glass and negatives slightly more 

 than an inch in diameter were obtained. These were 

 perfectly defined and bore a magnification of more than 

 16 diameters. In 1859, at the British Association meet- 

 ing held at Aberdeen, De La Rue reported " On the 

 Present State of Celestial Photography in England," and 

 exhibited some of the fruits of his labour. Amongst the 

 specimens were positive enlarged copies of other nega- 

 tives, eight inches in diameter, which would bear still 

 further enlargement, and instantaneous pictures of the full 

 moon. It was noted that very strong pictures of the full 

 moon were produced with exposures from one to five 

 seconds, and that the crescent moon required from twenty 

 to thirty seconds. A great part of the report was devoted 

 to a discussion of the methods adopted in taking stereo- 

 scopic pictures of the moon, many photographs of this 

 character being exhibited at the meeting. 



The extensive multiplication of enlarged copies of De 

 La Rue's negatives renders it unnecessary to expatiate on 

 their excellency. A magnificent series of twelve photos 

 was published in book form, and also enlarged so that 

 the lunar disk had a diameter of seventeen inches. In 

 this series the moon's progress was traced from the time 

 when she was six days old through the waxing and 

 waning periods to the 23! day. Each of the pictures was 

 a work of art, whilst the many details they contained gave 

 them a high scientific value, and conclusively demon- 

 strated the applicability of photography to the delineation 

 of celestial bodies. 



An enlargement three feet in diameter, from a negative 

 taken by De La Rue in 1858 is suspended in the library 

 of the Royal Astronomical Society. 



Rutherford began his work in lunar photography in 1858 

 with a refractor having a focal length of fourteen feet, and 

 an aperture of eleven and a quarter inches. Bv reducing the 

 aperture of the telescope to five inches for the full moon, 

 negatives were produced which would bear enlargement 

 to fifty diameters, or five inches. In the same year, whilst 

 De La Rue was obtaining stereoscopic pictures in England, 

 Rutherford was working in the same direction in America, 

 and with similar results. To the general public the 

 photographs taken by Rutherford in 1858 left little to be 

 desired, but they did not reach that degree of perfection 

 which is necessary to satisfy a scientifically cultured mind. 

 A mirror having a diameter of thirteen inches was there- 

 fore worked and fixed on the tube of the refractor in 1861. 

 The results obtained were, however, still deemed un- 

 satisfactory. The mirror soon became tarnished by the 

 action of the combustion products of the gas used for 

 illuminating purposes, while the motion of vehicles in the 



