470 PHOTOGRAPHY IN THE SERVICE OP ASTRONOMY. 



This applicatiou of photography is however so reasonable, its role was 

 so clearly indicated and so well foreseen, that it seems an equal prog- 

 ress ought to have been obtained indeed from the tirst. There was 

 one problem whose solution was perfectly circumscribed ; it was truly no 

 more than a question of time and money. The history of photography, 

 since its origin, is like the logical development of a thought which 

 is realized in a continuous manner before our eyes. The gropings by 

 which we discover substances more and more sensitive, or the means of 

 retaining, of fixing, more and more permanently, the fugitive traces of 

 phenomena, all these ought to be, most certainly, hastened and matured 

 more speedily in the fact of having a prize to gain; and here appear 

 clearlythe conditions always more tyrannical than expense in the scien- 

 tific enterprises of our epoch. 



Chemistry and the mechanical arts have singularly multiplied there- 

 sources of astronomers of the close of this century. Is there any occa- 

 sion to recall the progress accomplished in the manufacture and grind- 

 ing of optical glass, in the mounting of great telescopes, in silvered mir- 

 rors, in electric chronographs, in the spectroscope and in spectral analy- 

 sis, whose entry on the scene, so brilliant and so unexpected, probably 

 diverted for some time the attention of astronomers from the develop- 

 ment of photographic processes? Unhappily this instrument, so pow- 

 erful, this new apparatus which has extended the domain of observa- 

 tion, is very costly. In order to bring it into service, great efforts of 

 eloquence are almost always necessary, because the scientific budget, 

 as is well known, is one whose endowment is generally measured with 

 the greatest parsimony. It is in such a situation as this that the assem- 

 bly of a congress, with its solemn publicity, its persuasive programmes, 

 and its imperious desires, ofTers always the best means of overcoming 

 an opposition which is inspired by an ill-conceived economy. 



The congress which held its sessions at the Paris Observatory, two 

 years since, and which was called by Admiral Mouchez, under the 

 auspices of the Academy of Sciences, had in view, primarily, the exe- 

 cution of a chart of the sky. It comprised fifty astronomers, who came 

 from all parts of the globe, some already familiarized for a long time 

 with the pratique of celestial photography. 



It would be irksome to enumerate here even once, all the attempts 

 which have been made, since Daguerre, to bring photography into the 

 service of descriptive astronomy and the astronomy of precision. Ke- 

 callmg only that the most difficult part of the problem, the photographic 

 reproduction of stars, had been entered upon with some success in 

 America by G. P. Bond (soon after the introduction of the collodion 

 process permitted the shortening of the time of exposure), about 1857, 

 the photography of stars to the sixth or seventh magnitude had been at- 

 tained. These trials were repeated some years later in England by 



