CELESTIAL CHEMISTRY. 241 



*' Nehulce. — I pass now to objects of another order. 



" Wlien the eye is aided by a telescope of even moderate power, 

 a large number of faintly luminous patches and spots come forth 

 from the darkness of the sky, which are in strong contrast with 

 the brilliant but point-like images of the stars. A few of these 

 objects may be easily discerned to consist of very faint stars 

 closely aggregated together. Many of these strange objects re- 

 main, even in the largest telescopes, unresolved into stars, and 

 resemble feebly-shining clouds, or masses of phosphorescent 

 haze. During the last one hundred and fifty yeai's, the intensely 

 imjiortant question has been continually before the mind of 

 astronomers, ' What is the true nature of these faint, comet-like 

 masses ? ' 



"The interest connected with an answer to this question has 

 much increased since Sir William Herschel suggested that these 

 objects ai"e portions of the primordial material out of which the 

 existing stars have been fixshioned, and, further, that in these ob- 

 jects we may study some of the stages through Avhich the suns 

 and planets pass in their development from luminous cloud. 



"The telescope has failed to give any certain information of 

 the nature of the nebulte. It is true that each successive increase 

 of aperture has resolved more of these objects into bright points ; 

 but, at the same time, other fainter nebulas have been brought into 

 view, and fastastic wisps and diffused patches of light have been 

 seen, which the mind almost refuses to believe can be due to the 

 united glare of innumerable suns still more remote. 



" Spectrum analysis, if it could be successfully applied to ob- 

 jects so excessively faint, was obviously a method of investigation 

 specially suitable for determining whether any essential physical 

 distinction separates the nebulae from the stars. 



"I selected, for the first attempt, in August, 1864, one of the 

 class of small but comparatively bright nebulae. 



"My surprise was very great, on looking into the small tele- 

 scope of the spectrum apparatus, to perceive that there was no 

 appearance of a band of colored light, such as a star would give ; 

 but, in place of this, there were three isolated bright lines only. 



" This observation was sufficient to solve the long-agitated 

 inquiry-, in reference to this object at least, and to show that it was 

 not a group of stars, but a true nebula. 



"A spectrum of this character, so far as our knowledge at 

 present extends, can be produced only by light which has ema- 

 nated from matter in the state of gas. The light of this neinila, 

 therefore, was not emitted from incandescent solid or liquid 

 matter, as is the light of the sun and stars, but from glowing or 

 luminous gas. 



"It was of importance to learn, if possible, from the position 

 of these bright lines, the chemical nature of the gas or gases of 

 which this nebula consists. 



"Measures taken by the micrometer of the most brilliant of the 



bi'ight lines showed that this line occurs in the spectrum veiy 



nearly in the position of the brightest of the lines in the spectrum 



of nitrogen. The experiment was then made of comparing the 



21 



