PROBLEMS OF MODERN SCIENCE 



registers at one and the same time many distinct 

 objects, and the records thus obtained are perma- 

 nent and can be re-examined whenever it may be 

 desired. In addition it possesses this great superior- 

 ity over the eye, that by prolonging the time of ex- 

 posure, impressions of objects can be obtained whose 

 light is too faint to affect the most sensitive vision. 



One has only to compare recent photographs 

 of nebulas, showing a wealth of detail, with the 

 crude drawings of the same objects made after 

 many hours of patient examination, to realise 

 how enormous is the advance in the knowledge 

 of those objects which the employment of photo- 

 graphy has rendered possible. 



Moreover, in recent years telescopes greatly 

 exceeding all former ones in light-gathering 

 capacity and the perfection of their optical parts 

 have been constructed they all belong to the 

 other side of the Atlantic, one notes with some 

 regret and with these vast regions of space which 

 hitherto were utterly beyond reach are now being 

 explored. The result of these and other improve- 

 ments in the instruments of research is that data 

 are being accumulated at a rate altogether impos- 

 sible in former years, and astronomers are now 

 almost overwhelmed with the abundant material 

 pouring in upon them. 



The application of photography on a large 

 scale began in 1887, when a scheme was set afoot 



