98 Dr. J. E. Mills on the Relation of 



where fi is a constant for any given species of molecule, m is 

 the mass of the molecule, and 5 is the average distance apart 

 of the molecules. This interpretation considers the attractive 

 force of a given molecule as a definite and constant property 

 of the molecule, not capable of indefinite multiplication by 

 the introduction of other molecules into the surrounding 

 space. This definite force is absorbed or used up at an 

 average distance s depending upon the distance apart of the 

 molecules. This view is fully discussed in the article in the 

 Journ. Phys. Chem., May 19il. 



If the law of the molecular force is known it would seem 

 on first inspection a simple matter to write the general 

 equation of state for any substance, but such is by no means 

 the case. Temperature has per se no influence upon the 

 molecular attraction. The constancy of the results shown at 

 different temperatures in Table I. for the substances examined 

 is conclusive evidence upon that point. But it should be 

 noted that while equation 1 is tested for each substance over 

 a very wide range of temperature, yet during each individual 

 test the temperature is constant, since the substance tested 

 each time simply changes from liquid to vapour under a 

 definite pressure and at a definite temperature. While, there- 

 fore, the constancy of the results at different temperatures 

 as shown in Table I. is conclusive evidence that the change 

 of temperature in the substance has not changed the attrac- 

 tive force operating between the molecules, yet the temperature 

 has heen one factor determining the vapour pressure and the 

 densities of liquid and vapour at each temperature. The 

 question to be now considered is, In what way does the effect 

 of temperature combine with the law of molecular attraction 

 in order to produce a given density under a given pressure ? 



The problem is by no means easy of solution for reasons 

 that will later appear. It seems best, therefore, first to 

 consider carefully and fully the energy relations of two 

 masses governed by the law of attraction given. Then later 

 to apply the knowledge obtained, so far as can be clone, to 

 n masses. 



The law given in equation 2 for the molecular force differs 

 in some respects from the law of gravitation, and yet I have 

 stated at length * reasons for believing that both the molecular 

 force and the gravitational force are identical in origin and 

 character and are governed by the same law. It is not 

 possible to go into this discussion here further than to say 

 that the law given in equation 2 deals with the totality of 

 the force of a given molecule or mass, while Newton's law 

 * Journ. Phvs. Chem., May 1911. 



