PHOTOGRAPHING THE STARS. 293 



novel. Nor can we for that matter deny that the electric 

 light was invented half a century ago. But just as a few 

 brilliant inventions have transformed electrical lighting 

 from a scientific curiosity into an eminently practical 

 reality, so the recent improvements in photography have 

 rendered that art an indispensable auxiliary in the ob- 

 servatory of the future. 



The applications of photography to astronomy are of 

 the most widely diverse kind. We may employ it, in 

 the first place, as an auxiliary in the production of accu- 

 rate pictorial representations of particular objects in the 

 universe, or in obtaining views of groups of such bodies ; 

 we may also employ it to aid the process of exact mea- 

 surement. There are still other and more delicate 

 branches of practical astronomy where the photograph 

 is not merely a rapid or a convenient means of doing 

 what could otherwise not be done so conveniently. Photo- 

 graphy is a process for actually observing phenomena in 

 such cases as entirely elude ordinary vision, and are only 

 perceptible by the peculiar sensibility of the salts of silver 

 contained in the film. 



We shall first say a few words with regard to the suita- 

 bility of the new method for the purpose of recording 

 the appearances of the different celestial bodies. In all 

 the applications of this process to the heavens we must 

 bear in mind how widely different are the conditions 

 under which a celestial photograph is to be procured from 

 those which are met with in the more familiar pursuit of 

 the art. In taking a portrait with the camera, there is of 

 course only a few feet between the plate and the setter. 

 In the application of photography to the representation 



