236 Intelligence and Miscellaneous Articles. 



about it I would point to that paper. In the first place, he does not 

 speak of it ; and in the second place, when about to calculate the 

 amount of heat produced in the cell of a voltaic pair composed of 

 zinc and silver, he says (p. 266 of the paper he refers to in vol. xix. 

 Phil. Mag. 1841), "Before I proceed to give an account of some 

 experiments on heat evolved in cells of voltaic pairs, it is important 

 to observe that every kind of action not essentially electrolytic must 

 be eliminated," &c. He then, in calculating the heat produced, 

 makes allowance for the combination of the oxide of zinc and sul- 

 phuric acid, but does not at all mention the absorption of heat pro- 

 duced by decomposition of the water, which is of greater amount, in 

 the opposite direction. 



The several data to be taken into account in calculating the amount 

 of heat produced by the solution of zinc in sulphuric acid are, — the 

 oxidation of the zinc, the combination of the oxide of zinc and acid, 

 and the absorption of heat by decomposition. This last Mr. Joule 

 does not allude to at all ; and when it is considered that he sets 

 out with the determination to eliminate all actions which might in- 

 terfere with the proper amount of heat being arrived at, it must be 

 concluded that at that time he did not know that heat was absorbed 

 by decomposition. 



Now as to Mr. Joule's second charge, that I set up one part of 

 his papers against another, I can only say I merely quote his own 

 words to show that opinions he once held he afterwards altered, and 

 that I endeavoured to show his first opinions were correct. If any 

 contradiction appears, he should rather blame himself than me. He 

 says I erroneously suppose he contradicts himself. The matter stands 

 thus : — Mr. Joule proved experimentally (vol. xx. Phil. Mag. 1842) 

 that the amount of heat produced by oxidation might be taken as a 

 measure of the intensity of the attraction of affinity between the 

 combining bodies ; but in a subsequent paper (Phil. Mag. vol. xxiii. 

 p. 442) he says that " it is not precisely the attraction of affinity, &c. 

 which determines the intensity of the current and consequently the 

 amount of heat evolved." This is the contradiction he says I erro- 

 neously imagine. Without being aware that these papers had been 

 published, I had myself proved experimentally the first proposition ; 

 and when Mr. Joule claimed it, I at once, on referring to his first 

 publication, admitted his claim ; but added, that if the proposition 

 were true I should still consider I established it, as that although he 

 first held, he afterwards rejected it. 



In endeavouring to establish a claim to a disputed discovery, it is 

 impossible not to make reference to previous papers written by the 

 disputing parties. I have done so without having the least wish to 

 take any undue advantage of anything which has been written, or 

 which has not, but which ought to have been written if the truth 

 had been recognized. I trust that nothing I have said can make it 

 appear that I have not the highest respect for such a philosopher as 

 Mr. Joule, of whose high talents and achievements in science his 

 , country ought to feel proud; or that I am not deeply grateful for 



