48 THE HUMAN MOTOR 



in the dynamic sense of that form of energy. Henry Le Chatelier 

 has given it concrete expression in the law of the displacement of 

 equilibrium or Le Chatelier's law : "Any system producing work 

 is the seat of a disturbance of equilibrium. Conversely, wherever 

 there can be re-establishment of that equilibrium, there can be 

 production of work." ( l ) Carnot had shown the disturbance of 

 thermal equilibrium in the difference .of temperature between 

 the steam coming out of the boiler and the water going into 

 the condenser, a difference analogous, in the fall of water, to 

 the vertical distance between the head and tail race, by virtue 

 of which the water does work. There are two components of 

 each kind of energy, thus : Mechanical energy = force (or 

 weight) X the distance traversed ; heat energy = entropy ( 2 ) 

 X difference of temperature. 



Entropy is a quantity which varies with the absolute tempera- 

 ture as gravity varies on the surface of the earth with the distance 

 from the centre. When a substance takes in or gives out heat 

 it is said to change its entropy. 



Electric energy quantity of electricity X difference of the 

 potential ( 3 ) 



Chemical energy mass x chemical potential. 



The chemical potential expresses what is also understood by 

 the term "affinity," now obsolete. 



To return to calorific energy : it has been said that it is pro- 

 portional to the change of temperature. If, therefore, it is 

 transformed into mechanical energy, this in its turn will be 

 proportional to the same change of temperature. Now, steam 

 increases in pressure with the temperature by | of its value 

 for 1 degree C ; if in a heat engine, the temperature of the con- 

 denser is reduced by 1 , 2, 3 . . . degrees, the work will increase 

 by 



J_ JL JL 



273' 273' 273 



of its value. In cooling to 273, all the heat will be transformed 

 into work. A condenser at 273C would be at absolute zero ; 

 a fictitious temperature serving as the basis of an absolute scale. 

 Thus 15 centigrade represents an absolute temperature of 



288 = 273 + 15. 



(*) Henry Le Chateliu, Lecons sur le Carbone. We have drawn largely 

 on the ideas set forth in this authoritative work. 



( 2 ) The conception of entropy is due to a learned German physicist, 

 Clausius (1857). 



( 3 ) We say briefly : intensity X potential, or if we use the corresponding 

 electrical units : amperes volts. 



