A HALF-CENTURY OF SCIENCE. i 93 



A HALF-CEXTITKY OF SCIENCE.* 



By Sir JOHN LUBBOCK. 

 II. 



IN astronomy, the discovery in 1845 of the planet Neptune, made in- 

 dependently and almost simultaneously by Adams and by Le Ver- 

 rier, was certainly one of the very greatest triumphs of mathematical 

 genius. Of the minor planets, four only were known in 1831, while 

 the number now on the roll amounts to 220. Many astronomers be- 

 lieve in the existence of an intra-Mercurial planet or planets, but this is 

 still an open question. The solar system has also been enriched by 

 the discovery of an inner ring to Saturn, of satellites to Mars, and of 

 additional satellites to Saturn, Uranus, and Neptune. 



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 Wollas- 

 ton, who noticed a few of them ; but they were independently dis- 

 covered by Fraunhofer, after whom they are justly named, and who, 

 in 1814, mapped no fewer than 576. The first steps in "spectrum 

 analysis," properly so called, were made by Sir J. Herschel, Fox Tal- 

 bot, and by Wheatstone, in a paper read before this Association in 

 1835. The latter showed that the spectrum emitted by the incandes- 

 cent vapor of metals was formed of bright lines, and that these lines, 

 while, as he then supposed, constant for each metal, differed for dif- 

 ferent metals. " We have here," he said, " a mode of discriminating 

 metallic bodies more readily than that of chemical examination, and 

 which may hereafter be emjoloyed 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 

 gooSooo f 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 unex- 

 pected triumphs. Fraunhofer himself noticed the coincidence between 

 the double dark line D of the solar spectrum and a double line which 

 he observed in the spectra of ordinary flames, while Stoke* pointed out 

 to Sir W. Thomson, who taught it in his lectures, that in both cases 

 these lines were due to the presence of sodium. To Kirchhoff and Bun- 

 sen, however, is due the independent conception and the credit of hav- 

 ing first systematically investigated the relation which exists between 



* Presidential address before the York Meeting of the British Association for the Ad- 

 vancement of Science. 



vol. xx. 13 



