494 Dr. J. E. Mills on the 



back the atmosphere is readily calculated. There is a 

 surplus. Again there is no a priori method of deciding 

 whether any or all of that surplus actually did go to over- 

 come molecular attraction. It might have been used to 

 increase the kinetic energy of the individual molecules. It 

 might have been used — in part at least — to effect certain 

 chemical changes, or other interatomic actions. If no other 

 fact be taken into consideration, and no hypothesis be 

 allowed, it clearly would be impossible to determine how 

 much energy went to overcome molecular attraction, and 

 consequently the actual law of the attraction could not be 

 determined. 



In a search dor the true law of molecular attraction from 

 among the infinite suppositions which a complete ignorance 

 of the facts would make possible, two limitations exist and 

 should serve as a guide to our work. These are mentioned 

 below. 



3. The first limitation might be called the simplicity of 

 nature. The numerous compounds in the universe are made 

 up of perhaps about eighty elements. These elements, it is 

 very probable, are themselves composed of one or more very 

 much simpler bodies. These bodies have doubtless certain 

 properties as to shape, size, motion, &c, and the intricacy of 

 things as we see them is produced doubtless from the 

 action of a very few simple laws. The motions of the 

 planets are complex, but the laws that cause these motions 

 are very simple. The very fact that we search for a law of 

 molecular attraction (instead of supposing that each attraction 

 is different) is itself a recognition of the simplicity of nature. 



Has not Kleeman perhaps lost sight of the probable 

 simplicity of nature when he produces * as his fundamental 

 equation for the heat of vaporization, L, the following 

 relation : — 



m 



4 j> * 1.^4-) 



\_n,w,u,vj ' \x c I c / 



- 6 

 -1 



m \_n,w,u,vj T \X C L c / z 2 



where 



am 



c 2 = x h \/ { (n + w) 2 + u 2 + v 2 }. 

 It is not necessary to explain the meaning of the symbols. 

 * Phil. Mag. October 1911, p. 567. 



