PHOTOGRAPHING THE STARS. 317 



enco, and show that the stars of the Pleiades seem to have 

 resulted from the condensation of a mighty nebula, some 

 portions of which are still in the vicinity of the group. It 

 seems clear that the results obtained in the case of the 

 nebula in Andromeda, and of the Pleiades, would be alone 

 sufficient to justify all the expenditure of time and trouble 

 made on behalf of celestial photography. 



Several photographs of the great nebula in Orion have 

 also been taken, those of the Lick and Yerkes Observatories 

 being especially successful. It would seem, however, as 

 if the bluish nebulge, such as Orion and the Dumb-bell, 

 did not admit of such good photographic portraits as the 

 nebula in Andromeda which is of a whiter hue. The draw- 

 back to all nebular photographs is that, to give sufficient 

 exposure for the faint parts, the bright parts must be over- 

 exposed, while the stars are of course burnt into dis- 

 figuring blotches. 



It does not enter into the scheme of this chapter to discuss 

 with any detail the splendid applications of photography 

 to the spectroscopic study of the heavens. Here, indeed, 

 the pre-eminent utility of photography comes out most 

 distinctly. I must, however, give a few concluding lines 

 to the subject. In this department of celestial spectro- 

 scopy Sir William Huggins, K.C.B., is the most renowned 

 discoverer, and he has obtained exquisite photographs of the 

 spectra of stars. The white stars, such as Sirius and Vega, 

 show a truly marvellous spectrum ; there are a few lines 

 in the visible part, and a great number of lines in the 

 photographic part, due to hydrogen. The spectra of comets 

 and of nebulae have also been obtained, and are replete 

 With truly marvellous interest and instruction, 



