Manchester Memoirs, Vol. Ixv. (1921), No. 3 11 



lure and expanded to atmospheric pressure in the motor 

 cylinder. It includes a pump and a motor cylinder, and heat 

 is applied externally but internal combustion is suggested. 

 The engine is unworkable, but interesting, as it follows a type 

 which was experimentally operated by Sir George Cayley 

 many years before. Ericsson also was building an engine 

 of this type in America which he applied to a ship. Curiously 

 Joule seemed quite unaware of the existence of earlier pro- 

 posals. 



Joule's paper is interesting as showing the ideas of the 

 time as to air motive power as worked out on carefully ascer- 

 tained data. 



Thomson contributes a note to the paper on March 23rd, 

 1852, in which he calculates the Carnot cycle as applied to 

 an air engine. 



At a later date Joule and Thomson worked in conjunction 

 and discovered most important facts on the properties of air 

 and other gases during compression and expansion. 



Joule was most accurate and resourceful in the experi- 

 mental work, while Thomson was brilliant in his mathematical 

 treatment — he rapidly developed the science of thermodyna- 

 mics in its present form. With Joule he deduced the 

 universal laws as to conservation of energy, and showed 

 notwithstanding that energy was made unavailable by fall to 

 uniform temperature ; that is, there was dissipation of avail- 

 able energy although no energy was destroyed. 



Osborne Reynolds 1 was of opinion that one reason for 

 Joule's marvellous success in experiments compared with the 

 physicists of the day was due to the fact 



" That he (Joule) possessed the engineer's rather than 

 the philosopher's knowledge of mechanics proved one of 

 the happiest circumstances ; as he was thus familiar with 

 the only measure of mechanical action which directly 

 measured the mechanical effect of the physical actions he 

 was about to study." 



This is undoubtedly true, but there is a further fact which 

 aided Joule; he followed the typically English method of 

 induction and not deduction. 



The deductive method starts with a broad general theory 

 and deduces from that theory the particular facts to be 



1. I am greatly indebted to the excellent Memoir on Joule by the late 

 Professor Osborne Reynolds, published by The Manchester Literary and 

 Philosophical Society in 1892. 



