Prof, Tyndall's Notes on Scientific History, 4*7 



whose name, to ray deep regret, he has never yet named in con- 

 nexion with this question, though Mayer's relation to it has been 

 now for two years known to him. But this is not all. In public 

 and in private — in articles which are so far manly as to bear 

 their author's names, and in an article which bears no name, but 

 which has been recently mentioned with commendation in the 

 pages of this Magazine — I have been attacked for my support of 

 Dr. Mayer in language which I would not stoop to characterize. 

 While here, from the pen of the man who, in equal ignorance 

 both of me and of the facts, instituted this ungentle crusade 

 against me, I extract testimony to the greatness of Mayer's 

 work, stronger than I have ever uttered in attempting to vindi- 

 cate his claims. 



X. 

 56. Sir W. Herschel had called the maintenance of solar heat 

 "The Great Secret." Mayer endeavoured to solve it, and published 

 his essay on Celestial Dynamics in 1848. It will be seen, however, 

 in a foregoing page that the idea of a meteoric source of solar 

 heat was at his hand in 1845. His calculation of the quantity 

 of heat which would be generated by the mechanical combination 

 of the earth and sun proves this (see 22). But in 1848 he pub- 

 lished a complete development of his theory, and his essay is now 

 readily accessible since its translation by Dr. Debus for the Philo- 

 sophical Magazine *. There could scarcely be a closer coincidence 

 between two independent scientific memoirs than that subsisting 

 between the essay of Dr. Mayer and the paper of Prof. Thomson, 

 published six years subsequently f. Thomson considers and 

 rejects the assumption that the sun is a heated body, losing 

 heat ; Mayer did the same. Thomson considers and rejects the 

 assumption that the heat of the sun is due to chemical action ; 

 so did Mayer. Thomson considers and embraces the theory 

 that meteors falling into the sun give rise to his heat ; so did 

 Mayer. Thomson arrives at the conclusion that the main source 

 of solar light and heat is the zodiacal light. This was also 

 Mayer's conclusion. Their calculations run parallel, and their 

 deductions from them are the same. As an instance of coinci- 

 dence in detail the following is worthy of notice : — " A dark 

 body," writes Prof. Thomson in 1854, " of dimensions such as the 

 sun, in any part of space, might, by entering a cloud of meteors, 

 become incandescent as intensely in a few seconds, as it could 

 in years of continuance of the same meteoric circumstances, and 

 again getting to a position in space comparatively free from 

 meteors, it might almost as suddenly become dark again. It is 

 far from improbable that this is the explanation of the appear- 

 * Vol. xxv. pp. 241, 387, 417. 

 t Phil. Mag. vol. viii. p. 409. 



