4 THE PHYSICAL SIGNIFICANCE OF ENTROPY 



mean distance between adjacent atoms, and that between collisions 

 the mean length of the particle's path is great in comparison with 

 the average distance between the particles. Later on we will indi- 

 cate in a very general and brief way how the entropy idea may 

 be extended to other states of aggregation and to other than 

 purely thermodynamic phenomena. Mostly, therefore, we will 

 only consider states and processes in which heat phenomena and 

 mechanical occurrences take place. 



