$34 Intelligence and Miscellaneous Articles, 



to the discovery which I am sure the scientific world will allow me 

 when the matter is properly weighed, were it not for the statement 

 Mr. Joule makes at the commencement of his reply in your Maga- 

 zine for the present month. He says I mis-state the results he 

 arrived at, and that I endeavour to support my claim to an original 

 discovery by setting one part of his papers against another. 



To neither of these accusations can I silently submit. As to the 

 first, my statement is, that Mr. Joule passed a galvanic current 

 through a wire and found a certain quantity of heat generated, and 

 that he then passed it through an electrolyte and did not find the 

 same amount of heat produced for an equal resistance. There is no 

 mis-statement in this ; and Mr. Joule in his reply shows it so clearly, 

 that I have only to quote his own words to prove it. He says (p. 155 

 of the Number of this Magazine for this month), " Suppose, first, 

 we take a voltaic battery of 20 iron zinc pairs, and connect its ter- 

 minations by a metallic wire. After a certain interval of time, we 

 find 100 atoms or chemical equivalents of zinc dissolved in each cell 

 of the battery. Then the entire amount of heat evolved will be ex- 

 pressed by 100 X20= 2000. Suppose, secondly, we employ the same 

 battery to decompose water ; the virtual intensity of the entire bat- 

 tery circuit will then be 20 — 3i=16f (see p. 272 of the above- 

 mentioned memoir) ; and when 100 atoms of zinc in each cell of the 

 battery have been dissolved, or what comes to the same thing, when 

 100 atoms of hydrogen have been liberated in the decomposing 

 cell, the heat evolved by the entire circuit will be expressed by 

 100 X 16|= 1666. The difference between 2000 and 1666, or 334, 

 represents of course the heat taken up in eflfecting the separation of 

 the 100 atoms of hydrogen from 100 atoms of oxygen, and libera- 

 ting them in a gaseous state." Now here, when the metallic wire is 

 used, there are 2000 units of heat produced ; but when the electro- 

 lyte is used there are only 1666. The same amount of heat is not 

 evolved in the first and second case ; such is the result I stated he 

 arrived at, and such he says is a mis-statement. I do not under- 

 stand why he makes the assertion. There is a diflference, 334, 

 between the result of the two experiments ; and the cause of this 

 diflference, or rather the first determination of the cause, is just the 

 question at issue between Mr. Joule and me. He says, "it repre- 

 sents of course the heat taken up by the separation of the oxygen 

 and hydrogen." Of course it does; but when did Mr. 3 om\q first 

 tell the world of this simple fact ? Nine months after I published it 

 in October 1851 in this Magazine. In 1841 Mr. Joule published 

 a paper in the Philosophical Magazine proving, that the heat deve- 

 loped by a galvanic current is proportional to its intensity. When 

 the current passed through an electrolyte, Mr. Joule thought part 

 of the intensity was used up in causing electrolysis, and that the 

 remainder only was etFective in producing heat ; that for this reason 

 (to use his own example already quoted), instead of 2000 units there 

 ■were only 1666 units of heat produced ; ascribing the difference 334, 

 not to the separation of the oxygen and hydrogen, as he does now, 

 but to the diminished intensity of the battery. In this supposition, 

 however, he was quite in error. There is no loss of intensity or 



