4 M. R. Clai\sius on the Moving Force of Heat, 



it or refuting it. Besides this, I do not imagine that the diffi- 

 culties arc so great as Thomson considers them to be ; for although 

 a certain alteration in our way of regarding the subject is neces- 

 saiy, still I find that this is in no case contradicted by proved 

 facts. It is not even requisite to cast the theory of Carnot over- 

 board ; a thing difficult to be resolved upon, inasmuch as expe- 

 rience to a certain extent has shown a surprising coincidence 

 therewith. On a nearer view of the case, we find that the new 

 theory is opposed, not to the real fundamental principle of Carnot, 

 but to the addition "no heat is lost;" for it is quite possible 

 that in the production of work both may take place at the same 

 time ; a certain portion of heat may be consumed, and a further 

 portion transmitted from a warm body to a cold one ; and both 

 portions may stand in a certain definite relation to the quantity 

 of work produced. This will be made plainer as we proceed ; 

 and it will be moreover shown, that the inferences to be drawn 

 from both assumptions may not only exist together, but that 

 they mutually support each other. 



1. Deductions from the principle of the equivalence of heat and 



work. 



We shall forbear entering at present on the nature of the 

 motion which may be supposed to exist within a body, and shall 

 assume generally that a motion of the particles does exist, and 

 that heat is the measure of their vis viva. Or yet more general, 

 we shall merely lay down one maxim which is founded on the 

 above assumption : — 



Li all cases where work is produced by heat, a quantity of heat 

 proportional to the work done is eapended; and inversely, by the 

 expenditure of a like quantity of work, the same amount of heat 

 may be produced. 



Before passing on to the mathematical treatment of this maxim, 

 a few of its more immediate consequences may be noticed, which 

 have an influence on our entire notions as to heat, and which are 

 capable of being understood, without entering upon the more 

 definite proofs by calculation which are introduced further on. 



We often hear of the total heat of bodies, and of gases and 

 vapours in particular, this tei-m being meant to express the sum 

 of the sensible and latent heat. It is assumed that this depends 

 solely upon the present condition of the body under considera- 

 tion; so that when all other physical properties thereof, its 

 temperature, density, &c. are known, the total quantity of heat 

 which the body contains may also be accurately determined. 

 According to the above maxim, however, this assumption cannot 

 be admitted. If a body in a certain state, for instance a quan- 

 tity of gas at the temperature t^ and volume Vq, be subjected to 

 various alterations as regards temperature and volume, and 



