174 POrULAR LECTURES AND ADDRESSES. 



the subject from a very different point of view, he 

 made, in his extension of the "Theory of Ex- 

 changes," l the still wider generalisation that the 

 radiating power of every kind of substance is equal 

 to its absorbing power for every kind of ray ; or 

 that Kirchhoff also should have in 1859 independ- 

 ently discovered the same proposition, and shown 

 its application to solar and stellar chemistry ; but 

 because we might now be in possession of the 

 inconceivable riches of astronomical results which 

 we expect from the next ten years' investigation 

 by spectrum analysis, had Stokes given his theory 

 to the world when it first occurred to him. 



To Kirchhoff belongs, I believe, solely the great 

 credit of having first actually sought for and found 

 other metals than sodium in the sun by the method 

 of spectrum analysis. His publication of October 

 1859 inaugurated the practice of solar and stellar 

 chemistry, and gave spectrum analysis an impulse 

 to which in a great measure is due its splendidly 

 successful cultivation by the labours of many able 

 investigators within the last ten years. 



1 AV///. Transactions, 1858-59. 



