210 Professor Joseph Larmor [May 1, 



tion of work, where the body in action remains in the same state 

 after the production as before, is in all cases accompanied by a trans- 

 mission of heat from a warm body to a cold one, it does not follow 

 that by every such transmission work is produced, for the heat may 

 be carried over by simple conduction ; and in all such cases, if the 

 transmission alone were the true equivalent of the work performed, 

 an absolute loss of mechanical force must take place in nature, which 

 is hardly conceivable. Notwithstanding this, however, he arrives at 

 the conclusion that in the present state of science the principle 

 assumed by Carnot is the most probable foundation for an investi- 

 gation on the moving force of heat. He says : ' If we forsake this 

 principle, we stumble immediately on innumerable other difficulties, 

 which, without further experimental investigations, and an entirely 

 new erection of the theory of heat, are altogether insurmountable.' 



" I believe, nevertheless, that we ought not to suffer ourselves to 

 be daunted by these difficulties ; but that, on the contrary, we must 

 look steadfastly into this theory which calls heat a motion, as in this 

 way alone can we arrive at the means of establishing it or refuting it. 

 Besides this, I do not imagine that the difficulties are so great as 

 Thomson considers them to be ; for although a certain alteration in 

 our way of regarding the subject is necessary, still I find that this is 

 in no case contradicted by p'ozW/r^fi^s. It is not even requisite to 

 cast the theory of Carnot overboard ; a thing difficult to be resolved 

 upon, inasmuch as experience to a certain extent has shown a sur- 

 prising 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 cjuantity of work produced. 

 This will be made plainer as Ave proceed ; and it will be moreover 

 shown that the inferences to be drawn from both assumptions may 

 not only exist together, but that tbey mutually support each other." 



This memoir, as Willard Gibbs justly claims in his obituary 

 notice (1889) of Clausius, laid securely the foundations of modern 

 thermodynamics. But it seems equally true that this high merit lies 

 mainly in the single remark at the end of the passage just quoted, 

 which resolved the difficulties that had stopped Thomson ; after 

 that the development, though luminously accomphshed, would have 

 been plain sailing to any first-class intellect. Thomson's great 

 memoir ' On the Dynamical Theory of Heat,' * in which he at once 

 connects Clausius' name with that of Carnot, appeared the following 

 year. After giving a demonstration of the principle of " Carnot and 

 Clausius " (§ 13), he proceeds (§ 14) to say that, about a year before, 



* Trans. R S. Edinburgh, March 1851. 



