THE AIM AND ACHIEVEMENTS OF SCIENTIFIC METHOD. Ill 



transactions in which temperature changes occur in terms of 

 motions and mass-coefficients only. The critical treatment to 

 which we have subjected the concepts, kinetic energy and heat, 

 has been sufficient to show that they belong to the order not of 

 primary facts but of secondary constructions. The substantial 

 shape we give them is legitimate if we remember that it 

 makes the results of experimental or mathematical investigation 

 " psychologically available." But the identification of heat as a 

 " form " of energy has no real value; merely extending, in fact, 

 the psychological usefulness of the substantial conception of 

 energy to render intelligible the fact that a change in the value 

 of the arithmetical quantity ^mv 2 may at times be accom- 

 panied by the appearance of temperature changes under 

 conditions which are conventionally described by the statement 

 that a quantity of heat has appeared or disappeared which 

 bears a definite ratio to the change in the value of the former 

 quantity. 



52. 



The correlation of temperature states with definite 

 quantities of mechanical work theoretically effected by Lord 

 Kelvin's absolute thermodynamic scale, would appear at first 

 sight to be, in effect, equivalent to the desired reduction. 

 Lord Kelvin's argument* showed that in a reversible heat 

 engine, the "efficiency" (that is, the ratio of the quantity 

 of heat converted into work by the engine to the total 

 quantity which it draws from the " source ") depends upon 

 nothing but the actual temperatures of the source and the 

 " condenser." Suppose, then, two reversible engines drawing 

 heat from the same source A but returning it (less the 

 equivalents of the work done by each) to different condensers 

 B and C. Let the engines work until each has drawn the 

 same total quantity of heat from A. Then the amounts of 

 work done will depend merely upon the temperatures of B 



* See Preston, Theory of Heat, p. 611 et seq. 



