It is said that the first photograph of a star was a daguerreotype of Vega taken at Harvard observatory on July 17, 185o, but want of sensitiveness made this process rather impracticable, and there was little success in stellar photography until the invention of the collodion plate that was used in America and England in 1852. In November 1857 a photograph of Ursae Majoris with its corn panion Alcor taken at Harvard was sent for exhibition at the Royal Astronomical Society by W. C. Bond, an exposure of 8o sec. having been given to photograph the 6th magnitude star with the 15 in. refractor. De la Rue at this time was making ex periments on the actinic power of Jupiter and Saturn compared with that of the moon, but his photographs did not show any details of the planetary surfaces. Under his direction also, and to his design a photoheliograph was made and set up at Kew ob servatory for the Royal Society, and the work of taking daily photographs of the sun, that has since been carried on success fully, at Greenwich and elsewhere, began at Kew in March 1858. In an attempt to photograph Donati's comet of that year, De la Rue was not successful though it was photographed by Usherwood, of Walton Common, in 7 sec. with a portrait lens of short focus.
Daguerreotypes of the sun taken by Foucault and Fizeau in 1845, and photographs of the solar eclipses of 1851 and were interesting as experiments, but the photographs taken by De la Rue and by Secchi of the total solar eclipse in 1860 were the first of this kind of real scientific importance, since they estab lished beyond doubt that the solar protuberances were really appendages of the sun and not of the moon. Ten years later, at the eclipse of Dec. 12, 187o, excellent photographs taken by A. Brothers at Syracuse supplied evidence that the corona was also of solar origin; and from that time a photographic picture of the sun's surroundings has always been an item in the pro gramme of eclipse observation. A series from 1896 to 1922 is published in the Phil. Trans. vol. 226 A, and as Appendix to vol. lxiv. of the Memoirs of the Royal Astronomical Society.
In the years after 1870 research and experiment in pho tography generally were made by many, among these being the researches of Capt. W. de W. Abney, R.E., made specially for their application to astronomy. It was decided, mainly at the in stigation of De la Rue, that photography should be used by the British expeditions in addition to visual observation for the Transit of Venus in 1874, and a considerable sum was granted for the expense of the work, which, so far as the process was concerned, was put in Abney's charge. He realized that the cir cumstances of the occasion would make a wet-plate process in applicable and, after experiments conducted at Chatham, recom mended the adoption of an albumen dry process, using a highly bromized collodion and strong alkaline development.
Without attempting to give any complete account of Abney's researches mention of the titles of two papers by him—On Dry Plate Processes for Solar Photography and On the Photographic Method of Mapping the Least Refrangible End of the Solar Spec trum—will indicate their bearing on astronomy. These papers represent a remarkable achievement in that Abney succeeded in producing a special photographic emulsion, sensitive to red light, which he used to map the solar spectrum far into the infra-red.
The limit of Abney's measures at 9867A apparently was not reached by any other investigator until the introduction of neocyanin as a sensitizer in 1926.
It was pointed out by the younger Bond that photography might be successfully used to measure the relative positions of stars, of a group, or of double stars and in a letter to the Hon. William Mitchell, dated July 6, 1857, predicted, in effect, the applkation of photography to stellar astronomy on the mag nificent scale that actually exists to-day. Rutherfurd, in 1864, began to make a long series of photographs of star clusters and of the bright double stars; but measures of these appear not to have been completed. In 187o-84 Dr. B. A. Gould in an expedi tion to the Southern Hemisphere accumulated negatives of the principal double stars and clusters; but in taking these series the wet plate process was used, and with this it was not possible to give an exposure long enough for faint stars to imprint themselves. With the invention of the gelatine dry plate, which had been used by Huggins for spectrum photography in 1876 and came into general use about 188o, this difficulty did not exist and modern astronomical photography became possible. Circumstances con nected with the comet of 1882, which was specially magnificent as seen from the Southern Hemisphere, led to developments. A photograph, taken with a camera strapped for the purpose to the great equatorial of the Royal observatory of the Cape of Good Hope, showed not only the comet but great numbers of faint stars around it, and this at once gave David Gill, H.M. Astronomer at the Cape, the idea of the possibility of making star charts by photography. Effects of various kinds followed. At Paris the brothers Henry of the National observatory were engaged in the laborious task of plotting the positions of stars found by eye observation to make charts of the stars near the Ecliptic ; but this work was abandoned and their efforts were devoted to making a telescopic object-glass suitable for photography. Ainslie Common in England turned to the art and with a three foot silver-on glass mirror took a photograph of the Orion Nebula on Jan. 3oth, 1883, with an exposure of 37 min., a feat that earned for him the Gold Medal of the Royal Astronomical Society in 1884, and was referred to as "epoch-marking" by Abney when presenting the medal to another non-professional astronomer for similar work eleven years later. A photograph of this object taken by Dr. Henry Draper of New York on Sept. 3o, 1880 is said to be the first of a nebula obtained, but it is agreed that this was not a satisfactory representation. The later recipient of the medal above mentioned was Isaac Roberts, a business man of Liverpool, who in 1885, had made a 20 in. silver-on-glass reflector of nearly a zoo in. focal length for the purpose originally of making star charts by photography, but altered his plans and devoted the instrument to photographing star-clusters and nebulae. The ex cellent pictures produced at his observatory at Crowborough, Sussex, are in two volumes published during his lifetime, supple mented by a third prepared and issued by his widow in 1928.