ASTRONOMY. SPECTRUM ANALYSIS. 47 



open question. The Solar System has also been en- 

 riched by the discovery of an inner ring to Saturn, of 

 satellites to Mars, and of additional satellites to Saturn, 

 Uranus, and Xeptune. 



The most unexpected progress, however, in our 

 astronomical knowledge during the past half-century 

 has been due to spectrum analysis. 



The dark lines in the spectrum were first seen by 

 \Yollaston, who noticed a few of them ; but they were 

 independently discovered by Fraunhofer. after whom 

 they are justly named, ond who, in 1814, mapped no 

 fewer than 576. The first steps in ' spectrum analysis,' 

 properly so called, were made by Sir J. Herschel, 

 Fox Talbot. and by Wheatstone. The latter, in a paper 

 read before this Association in 1835, showed that the 

 spectrum emitted by the incandescent vapour of metals 

 was formed of bright lines, and that these lines, while, 

 a> he then supposed, constant for each metal, differed 

 for different metals. ' ~\Ye have here,' he said, ' a mode 

 of discriminating metallic bodies more readily than that 

 of chemical examination, and which may hereafter be 

 employed for useful purposes.' Nay, not only can 

 bodies thus be more readily discriminated, but, as we 

 now know, the presence of extremely minute portions 

 can be detected, the 50 ooooo of a grain being in some 

 cases easily perceptible- 

 It is also easy to see that the presence of any new 

 simple substance might be detected, and in this manner 

 already several new elements have been discovered, as 

 I shall mention when we come to Chemistry. 



But spectrum analysis has led to even grander and 

 more unexpected triumphs. Fraunhofer himself noticed 



