Annual Report of the Council. xli 



•endeavoured to do," wrote Joule, "and a discussion not being 

 invited, the communication would have passed without comment 

 if a young man had not risen in the Section, and by his 

 intelligent observations created a lively interest in the new 

 theory. The young man was William Thomson." 



Lord Kelvin has given his account of the meeting. " I 

 heard his paper read at the Section, and felt strongly impelled 

 to rise and say that it must be wrong, because the true mechanical 

 value of heat given must, for small differences of temperature, be 

 proportional to the square of its quantity. I knew from Carnot's 

 law that this must be true. But as I listened on and on, I saw 

 that though Carnot had vitally important truth not to be 

 abandoned. Joule had certainly a great truth and a great 

 discovery . . . I said my say to Joule at the end of 

 the meeting. After that I had a long talk over the whole 

 matter at one of the conversaziones, and we became friends 

 from thence forward. . . . About a fortnight later I was 

 walking down from Chamounix, and whom should I meet 

 walking up but Joule, with a long thermometer in his hand, 

 and a carriage with a lady in it not far off. He told me he had 

 been married since we parted at Oxford, and he was going to 

 try for elevation of temperature in waterfalls." 



In the following year Kelvin alludes in a footnote to Joule's 

 researches, but in 1849 his paper on Carnot's theory of the 

 Motive power of Heat contains a more definite recognition : 

 " The extremely important discoveries recently made by Mr. 

 Joule, of Manchester, that heat is evolved in every part of a 

 closed electric conductor moving in the neighbourhood of a 

 magnet ; and that heat is generated by the friction of fluids in 

 motion, seem to overturn the opinion generally held that heat 

 cannot be generated, but only produced from a source where 

 it has previously existed." Kelvin could not then reconcile 

 Joule's results with Carnot's theorem, which he considered must 

 be still accepted as most probable. But in 185 1 Kelvin read 

 his classical memoir, showing that a complete theory of 



