132 THE CANADIAN NATURALIST. [Vol. vi. 



which had been shown to me by M. Dubosque Soleil, and the 

 Abbe Moigno, in Paris, in the month of October, 1850. A prism 

 and lenses were arranged to throw upon a screen an approximately 

 pure spectrum of a vertical electric arc between charcoal poles of 

 a powerful battery, the lower one of which was hollowed like a 

 cup. When pieces of copper and pieces of zinc were separately 

 thrown into the cup, the spectrum exhibited, in perfectly definite 

 positions, magnificent well-marked bands of difierent colours 

 characteristic of the two metals. When a piece of brass, com- 

 pounded of copper and zinc, was put into the cup, the spectrum 

 showed all the bands, each precisely in the place in which it had 

 been seen when one metal or the other had been used separately. 

 It is much to be reg-retted that this g-reat s-eneralization was 

 not published to the world twenty years ago. I say this, not be- 

 cause it is to be regretted that Angstrom should have the credit 

 of having, in 1853, published independently the statement that 

 " an incandescent gas emits luminous rays of the same refrangi- 

 bility as those which it can absorb" ; or that Balfour Stewart 

 should have been unassisted by it when, coming to the subject 

 from a very di0"erent point of view, he made, in his extension of 

 the ' Theory of Exchanges,' (Edin. Transactions, 1858-59,) the 

 still wider generalization that the radiating power of every kind 

 of substance is equal to its absorbing power for every kind 

 of ray ; or that Kirchoff also should have, in 1859, independently 

 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. 



2. SOLAR AND STELLAR CHEMISTRY. 



To Kirchhoff belongs, I believe, solely the great credit of hav- 

 ing 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. 



To prodigious and wearing toil of Kirchhofi" himself, and of 

 Angstrom, we owe large-scale maps of the solar spectrum, incom- 



