ON THE PHYSICAL VIEW OF NATURE. 117 

 still earlier writings of Sadi Carnot and Clapeyron in is. 



Sadi Carnot. 



France. Thomson's interest in the subject dates from 

 the middle of the 'forties. He was then occupied with 

 finding a method for measuring heat on the absolute 

 scale. Mohr, Mayer, and Helmholtz all approached the 

 thermo-dynamical problem in the medical or physiological 

 interest. Trained in the school of liebig and Johannes 

 Miiller, they were led to study the economics of organic 

 processes and the mechanism of the physiological pheno- 

 mena of animal heat, of motion, and of nutrition. Sadi 

 Carnot, as after him Clapeyron in France and Joule in 

 Manchester, approached the thermo-dynamical problem 

 from the side of practical interests, created by the intro- 

 duction and universal application of steam in the useful 

 arts. The great change worked by the steam-engine, 

 especially in England, the utilisation of coal and iron- 

 stone, the foundation of England's growing industrial 

 wealth, seemed to Sadi Carnot to be concentrated in the 

 problem of the motive power of heat; as to Liebig, the 

 key which would unlock the mysteries of vegetable 

 growth, of animal nutrition, and of human labour, with 

 their economic, industrial, and political aspects, lay in 

 the problem of combustion. As in the domain of electri- 

 cal science, so in that of thermotics, the first thing to 

 do was to arrive at a correct method of measuring heat 

 as distinguished from temperature. It was a problem of 

 applied mathematics. About the same time Gauss had 

 established the system of absolute measurement from a 

 universal point of view, and he and Weber had applied 

 it to magnetic and electrical phenomena. Thomson 

 set himself to do the same thing in thermotics, and 



