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XXVI. On the Principles of Thermodynamics. 

 By the Rev. J. M. Heath*. 



I HA VIS for some time past been challenging the attention of 

 scientific men to the consideration of a very important ques- 

 tion : — whether some of the most elementary principles in dyna- 

 mics have not been overlooked by those who originally framed 

 the language of thermodynamics; and whether their successors 

 have not indolently adopted that language, and the notions which 

 it was formed to embody, without using sufficient care to purify 

 it of those errors which the prepossessions and imperfect know- 

 ledge of the first investigators had made almost unavoidable in 

 them. 



Mr. Rankine has replied to me, in the August Number of this 

 Journal, to the effect that the principles I contend for are (as far 

 as he understands me) right ; and I think he must be taken as 

 admitting, by his silence, that they were in fact ignored by the 

 earliest original investigators in the science. But he tells me 

 that the more modern writers, at least the best among them, had 

 long ago perceived all that I have been pointing out, and have 

 so altered their creed and their language as to be free from the 

 reproach which I appear to make against them. 



In support of this statement, Mr. Rankine has given us two 

 propositions embodying the creed which is considered orthodox 

 at the present moment. Mr. Rankine* s name is so high an 

 authority upon this point, that there can be no question that 

 we have from him an authentic statement of what the present 

 doctrine is, which it is said is in strict harmony with all that 

 I have called for. If, therefore, I myself can make a similar 

 statement of my own opinions, we shall at once be enabled to 

 judge both whether the two doctrines are essentially one and the 

 same, as is alleged, or, if different, which of them has the best 

 claim to be accepted as representing the truth of the matter. 



I understand Mr. Rankine's first proposition to be, that if the 

 elasticity of a body results from the mutual attraction or repul- 

 sion of its particles acting upon one another, any forcible com- 

 pression of such a body would result in " stored-up energy," but 

 would be wholly incapable of producing (molecular motion or) 

 heat. And I think he imagines that this is the doctrine which 

 I have only just now come to perceive for myself and am bring- 

 ing forward as somewhat of a novelty; whereas it has long ago 

 been perceived by the best writers of the present time., and they 

 are one and all careful in all cases to separate the amount of 

 energy expended in this " storing-up of energy" by " overcoming 

 the resistance of repulsive forces " from the total amount, before 

 they estimate the remainder, which alone can produce heat. 

 * Communicated by the Author. 



