298 POPULAR SCIENCE MONTHLY. 



fortunately, two mathematicians proved to be equal to the task 

 of solving it — Adams, in England, and Le Verrier, in France. 

 Each of these astronomers, in independence of the other, suc- 

 ceeded in determining the place of the planet in the sky. The 

 dramatic incident of this discovery was afforded when the mathe- 

 maticians had done their work. When the place of the planet 

 had been ascertained, then the telescopic search was undertaken 

 to verify if it were indeed the case that a planet hitherto unknown 

 did actually lurk in the spot to which the calculations pointed. 

 Every one who has ever read a book on astronomy is well acquainted 

 with the wonderful manner in which this verification was made. 

 Just where the mathematicians indicated, there was the great planet 

 discovered! To this object the name of "Neptune" has been 

 assigned, and its discovery may be said to mark an epoch in the 

 history of gravitation. It provided a most striking illustration 

 of the truth of those great laws Avhich ISTewton had discovered. 



The latter half of the century will be also remarkable in the 

 history of science from the fact that within that period mankind 

 has been enabled to make some acquaintance with the chemistry 

 of the celestial bodies. It was in 1859 that Kirchhoff and Bunsen 

 first expounded to the world the true meaning of the dark lines in 

 the solar spectrum. In this they were following out a line of rea- 

 soning that had been previously suggested by Prof. Sir G. Stokes, 

 of Cambridge, England. Those who are at all conversant with 

 that wonderful branch of knowledge known as spectrum analysis 

 are aware how these discoveries have rendered it possible for us 

 to determine in many cases the actual material elements found in 

 the most distant bodies. 



One of the striking results to which this investigation has 

 led is the demonstration of the substantial unity of the mate- 

 rials from which the earth and the various heavenly bodies have 

 been constructed. Those elements which enter most abundantly 

 into the composition of the earth are also the elements which 

 appear to enter most abundantly into the composition of the sun 

 and of the stars. The iron and the hydrogen, the sodium and the 

 many other materials of which our globe is so largely formed, are 

 also the selfsame materials which, in widely different proportions 

 and in very different associations, go to form the heavenly bodies. 

 This conclusion is as interesting as it was unexpected. It might 

 naturally have been thought that, seeing the sun is separated from 

 us by nearly a hundred million miles, and seeing that the stars 

 are separated from us by millions of millions of miles, all these 

 celestial bodies must be constructed in quite a different manner 

 and of substances quite distinct from the substances which we know 



