6 Professor Dewar on The Scientific Worh of Joule. [Jan, 24, 



consequences, if true, to science. But all my arguments were 

 insufficient to convince my friend ; and I fear that then the Eoyal 

 Society did not appreciate and publish the researches. I write from 

 memory only, for I know that, later, no society or institution honoured 

 Joule more than the Eoyal Society and its members. 



Not for one moment, however, did Joule hesitate in the accuracy 

 of his experiments or his conclusions. He once suggested to me that 

 we might take a trip together to the Falls of Niagara, not to look at 

 its beauties, but to ascertain the dijSference of temperature of the 

 water at the top and bottom of the fall. Of course the change of 

 motion into heat was a necessary consequence of his views. 



No more pleasant memory of my life remains than the fact that, 

 side by side, at my lectures in the Eoyal Institution, used to sit the 

 illustrious Dalton, with his beautiful face, so like that of Newton, and 

 the keenly intelligent Joule. I can give no other explanation than 

 the fact of organic chemistry being then a new science that two 

 philosophers of such eminence should come to the lectures of a mere 

 tyro in science. I used to look upon them as two types of the highest 

 progress in science. Newton had introduced law, order, and number 

 into the movements of masses of matter in the universe ; Dalton 

 introduced the same into the minute masses which we call atoms; 

 and Joule, with a keen insight into the operations and correlation 

 of forces, connected them together and showed their mutual equi- 

 valence. 



I do not know whether these memories are of any use to you, but, 

 such as they are, they are at your disposal for your lecture on the 

 friend of my youth. 



Yours sincerely, 



Lyon Playfair. 



