THOMSON'S FIRST PAPER. I If 



This was not, as might naturally be supposed, inspired 

 by anything he had learned from Joule, but was obviously 

 the immediate result of the publication of Regnault's 

 researches, as affording data which enabled him to make 

 the numerical comparisons of the degrees centigrade with 

 those of the absolute scale which had been previously 

 suggested to him by Carnot's theorem. 



The paper itself is altogether pre-Joule, and serves well 

 to illustrate the state of assured error into which the 

 casuistry of the schools relating to caloric reduced the 

 minds of their most powerful and philosophical thinkers. 



It appears from a note, however, that his interview with 

 Joule had produced an effect which had not been altogether 

 obliterated by the intense occupation of the mean time. 



In his description of the foundation of Carnot's theory, 

 Sir William Thomson writes : — 



" In the present state of science no operation is known 

 by which heat can be absorbed, without either elevating the 

 temperature of matter, or becoming latent and producing 

 some alteration in the physical condition of the body into 

 which it is absorbed ; and the conversion of heat (or caloric) 

 into mechanical effect is probably impossible,* certainly 

 undiscovered. In actual engines for obtaining mechanical 

 effect through the agency of heat we must consequently 

 look for the source of power, not in any absorption or con- 

 version, but merely in a transmission of heat." 



The note to the asterisk over " impossible " is : — 



" This opinion seems to be nearly universally held by 

 those who have written on the subject. A contrary opinion, 

 however, has been advocated by Mr. Joule, of Manchester ; 

 some very remarkable discoveries which he has made with 

 reference to the generation of heat by the friction of fluids 



