The Rev. T. P. Kirkman's Note on Combinations. II 



ciple, that " the decomposition of a compound body occasions 

 as much cold as the combination of the elements originally pro- 

 duced heat/^ 



Mr. Joule_, in the introduction to his paper ^^ On the Heat dis- 

 engaged in Chemical Combinations/^ published in this Magazine 

 last July^ after noticing that I had proved the definite production 

 of cold by decomposition, adds, that previous to the year 1843 

 he had demonstrated '' that the heat rendered latent in the elec- 

 trolysis of water is at the expense of the heat which would other- 

 wise have been evolved in a free state by the circuit/^ But his 

 conclusions in no way interfere with mine, for he ascribes the 

 absence of heat to a cause quite different from absorption by 

 'decomposition. He reasons thus, if I understand him rightly : — A 

 current of a certain intensity passing through a conductor with 

 resistance produces a certain amount of heat. The same inten- 

 sity of current ought equally to affect water and a solid con- 

 ductor j but he proves less heat is produced by it in water ; and 

 ascribes as the reason, that a certain amount of the intensity is 

 used up in overcoming the obstruction offered by the decom- 

 position, and the residue of the current is alone concerned in 

 producing the heat. Now this explanation differs altogether 

 from that which ascribes to the decomposition itself the absorp- 

 tion of the heat. The latter is the principle I endeavoured to 

 establish in the paper published in this Magazine in October 

 1851, and by a similar process to mine, which Mr. Joule him- 

 self proves in the Number for July 1852. 



If it be true that decomposition occasions as much -cold as 

 combination of the same elements produces heat, is not Mr. 

 Joule's theory of the heat of combination being due to resistance 

 to electric conduction disproved ? 



I have the honour to be, &c., 



Thomas Woods. 



IV. Note on Combinations. 

 By the Rev. Thomas P. Kirkman, A.M. 



To the Editors of ttie Philosophical Magazine and Journal. 



Gentlemen, 



THE puzzle of the fifteen young ladies now takes rank as a 

 case of a mathematical problem, of no common interest, 

 from the analysis developed in its treatment. Mr. Anstice has 

 shown, in the Cambridge and Dublin Mathematical Journal, how 

 this kind of question may be brought under the mastery of 



