WEI.LS: PHYSICAIy VS. CHEMICAI, FORCES 363 



Whatever the nature of the fields of force, the effect of neigh- 

 boring systems would be expected to be more definite the more 

 discrete the structure. Thus electronic forces are definitely 

 characteristic of the nature of the element, showing the finite 

 differences of the periodic system. Atomic forces show more 

 continuity, only two distinct types occurring, corresponding to 

 primary and secondary valence. These may be called primary 

 and secondary atomic forces. Molecular systems have lost so 

 much of their discreteness that combinations of molecules do 

 no't follow the laws of definite and multiple proportions. In 

 such phenomena as molecular association and surface structure, 

 the discreteness of atomic constitution begins to give place to 

 statistical continuity. Moreover, even in these phenomena, 

 the forces are relatively so weak that molecules are not usually 

 regarded as permanently grouped together. 



In order to avoid the troublesome conflicts which are involved 

 in the use of the words physics, physical chemistry, and chemis- 

 try, for many purposes it would be convenient to classify these 

 portions of science into molar theory or molics, molecular theory 

 or moleculics,^ atomics, and electronics. 



Molics deals only with continuous quantities and ideal dis- 

 continuities such as surfaces. This is the province of classical 

 physics. In molecules the statistical nature of molar quantities 

 must be considered. For instance, actual surfaces between 

 distinct phases are not regarded as mathematical surfaces of 

 discontinuity, but as possessing a molecular structure, so graph- 

 ically shown by Langmuir and his predecessors. Such phenom- 

 ena as molecular association, condensation and those connected 

 with colloids and ions in gases are also typically molecular in 

 that finite groups of molecules are involved and the range of 

 forces is not large compared with the distances between mole- 

 cules. Moleculics thus includes much of what is often called 

 physical-chemistry. The complexity of molecular systems lim- 

 its the application of quantitative methods, in spite of the great 

 advances in statistical mechanics. 



3 The accent might be placed upon the penult, as in monalomic. 



