SECOND LAW OF THERMODYNAMICS 227 



THE SECOND LAW OF THERMODYNAMICS : ITS BASIS IN 

 INTUITION AND COMMON SENSE 1 



By Professor W. S. FRANKLIN 



LEHIGH UNIVERSITY 



IT is the object of this article to give a simple account of that funda- 

 mental principle in plrysics which is known as the second law of 

 thermodynamics. No generalization of modern physics is of greater 

 importance, not even the principle of the conservation of energy, and 

 no generalization of modern physics is based upon such deeply seated 

 and such widely diffused human intuitions. It is the purpose of this 

 article to give a sharp characterization to this widely diffused intuition. 



Thermal Equilibrium 



The most important single fact in connection with the study of the 

 phenomena of heat is that a substance settles to a quiescent state in 

 which there is no tendency to further change of any kind when it is 

 left to itself and shielded from all outside disturbing influences. This 

 quiescent state is called a state of thermal equilibrium. For example, 

 the various objects in a closed room settle to thermal equilibrium; 

 when a piece of red-hot iron is thrown into a pail of water, the mixture, 

 at first turbulent, becomes more and more quiet and finally reaches a 

 state of thermal equilibrium. A number of bodies which have settled 

 to a common state of thermal equilibrium are said to have the same 

 temperature. Thus a number of bodies left together in a closed room 

 have the same temperature. 



Atomics and Thermodynamics 



In nearly every branch of physical science there are two more or 

 less distinct modes of attack, namely, (a) a mode of attack in which 

 the effort is made to develop conceptions of the physical processes of 

 nature, and (6) a mode of attack in which the attempt is made to 

 correlate phenomena on the basis of sensible things, things that can be 

 seen and measured. In the theory of heat the first mode is represented 

 by the application of the atomic theory to the study of heat phenomena, 

 and the second mode is represented by what is called thermodynamics. 

 In the first case one tries to imagine the nature of such processes as 

 the melting of ice or the burning of coal, and in the second case one 

 is content to measure the amount of heat absorbed or given off and to 



1 The substance of this article will be incorporated in Franklin and Mac- 

 Nutt's " Elementary Theory of Heat," which is now in preparation. 



