528 



RICE 



ART. L 



he calls S. In the figure, K represents the closed surface which 

 cuts the surface S and includes part of the homogeneous masses 

 on each side; the portion of K which cuts S and is within the 

 non-homogeneous region is generated by a moving normal to S; 

 the remaining parts of K in the homogeneous masses may be 

 drawn in any convenient fashion. The portion of S referred 

 to by the letter s (m Clarendon type) is indicated by ^5 in the 

 figure, and its area is given by the italic s. CD and EF indi- 

 cate portions of the other two surfaces mentioned at the top of 

 page 220. The parts referred to in Gibbs' text by the letters, M, 

 M', M" are also indicated in the figure. In the succeeding 



K 



K 



Fig. 3 



paragraph the difficulty of defining the exact amounts of energy 

 to be attributed to masses separated from one another by a 

 surface Avhere a discontinuity exists is touched on, but, in view 

 of what has already been said above, this matter will probably 

 be easily grasped by the reader, and in the immediately follow- 

 ing pages the development follows that of the earlier parts of 

 Gibbs' treatise, i.e., on pages 65 ei seq. Great care is required 

 when we reach page 224 to observe just what Gibbs means by 

 the energy and entropy of the dividing surface S, and the 

 superficial densities of these and of the several components. 

 The definitions and arguments are quite clear, and the figure 



