3I4 IN STARRY REALMS. 



some wealthy Englishman to accomplish a work which 

 could be worthily mentioned beside the magnificent 

 Draper Memorial now being reared by Professor Pickering 

 in America. 



Hitherto I have spoken of photography merely as an 

 appliance for the simple purpose of charting or of mapping 

 the stars. It remains to mention some of the numerous 

 other applications of which it is susceptible. One of the 

 most delicate problems of celestial measurement is the 

 determination of the distance of a fixed star. This is 

 derived from a series of measures made at varying seasons 

 of the year between the star under examination and some 

 more distant star which happens to lie nearly in the same 

 direction of vision. If, therefore, a series of photographs 

 at different seasons be obtained, the measurements made 

 on these photographs will disclose the star's distance, if it 

 be sufficiently near to admit of the application of the 

 process. The late Dr. Pritchard, who had been a diligent 

 cultivator of the photographic methods, had already made 

 several successful attempts of this description by measures 

 on photographs which he had obtained in the University 

 Observatory at Oxford. 



The applications of photography to the stars which 

 I have already mentioned are mainly improvements on 

 methods formerly used, except indeed in so far as they dis- 

 close to us stars which are not visibly perceptible, but we 

 have now to speak of the manner in which photography 

 has laid open to us discoveries of the most remarkable 

 character in a province peculiarly its own. I can only 

 mention the two most remarkable instances. 



The great nebula in Andromeda is a familiar telescopic 



