Il8 MAINTAINS INCONVERTIBILITY OF HEAT. 



in motion, and some known experiments with magneto- 

 electric machines, seeming to indicate an actual conver- 

 sion of mechanical effect into caloric. No experiment, 

 however, is adduced in which the converse operation is 

 exhibited ; but it must be confessed that as yet much is 

 involved in mystery with reference to these fundamental 

 questions of natural philosophy." 



Clearly in the interval which elapsed between the 

 meeting at Oxford and the writing of the above, Sir 

 William Thomson had been otherwise engaged than in 

 mastering Joule's researches. 



This note of Sir William Thomson's contains the first 

 comments upon Joule's work published by any physicist 

 then, or afterwards, eminent. Coming, as it did, after 

 five years of absolute silence, and standing, as it does, alone 

 for another six months, it has great interest in Joule's 

 biography. 



In itself it certainly contains but little in the way of 

 recognition of the results of Joule's 10 years' labour. It 

 contains the mistaken denial that Joule had proved the 

 conversion of heat into work ; showing that Joule had been 

 too hasty in supposing that the results which were obvious 

 to him as a simple logical deduction from his experiment on 

 air and the, previously proved, experimental relations 

 between the pressures, volumes, and temperature would be 

 equally obvious to his readers. It also contains the still 

 more mistaken denial that any experiment had proved 

 the conversion of caloric (then used as including latent heat 

 with free heat) into mechanical effect, showing that the 

 writer had overlooked the direct proof of this contained in 

 Joule's magneto-electrical experiments — a proof, the beauty 

 of which the same writer, some two years later, not only 



