Law of Molecular Attraction. 495 



The expression for the internal heat of vaporization, X, as 

 actually deduced by the author and shown to be in accord 

 with the facts, is, 



X = constant 0^/ d — %y Id) . 



Here we only desire to contrast the equations as to 

 simplicity, remembering that such a test is justified by our 

 knowledge of nature and her laws. I do not mean to be 

 unfair to Kleeman. His equation is a general one, and 

 under certain conditions would, I think, reduce to mine. 

 I do mean to say that in my opinion the fundamental laws 

 of nature will prove to be simple, and that they can be 

 represented simply when they are understood. 



4. The second limitation is the limitation imposed by the 

 facts which it is possible to connect with the problem. By 

 making what I considered legitimate use of known facts, I 

 have escaped many difficulties and could approach a solution 

 of the problem of molecular attraction in a relatively simple 

 manner. 



5. I certainly agree that if we were completely ignorant 

 of other facts than a knowledge of the heat of vaporization 

 it would be impossible to deduce the law of molecular 

 attraction. But Kleeman apparently admits, or tentatively 

 admits, that our knowledge enables us to connect the internal 

 heat of vaporization, X, with the changes in density of the 

 substance p according to an equation, 



*=+G») (5) 



From this fact alone — the fact that the internal latent 

 heat is some function of the density of the substance — 

 Kleeman deduces the statement that the internal heat and 

 the density of a substance can be connected by an infinite 

 number of equations. 



It is perfectly true that both sides of equation (5) can be 

 multiplied or divided by the same quantity, or increased or 

 diminished by the same quantity, and thus an infinite 

 number of equations can be obtained. But these equations 

 are all identical, and it would certainly be misleading to 

 speak of them as an infinite number of equations connecting 

 the same two quantities. 



Moreover, a transformation of coordinates could be made, 

 or other changes could be made in our symbols of expression, 

 and thus the relation between p and X could be expressed in 

 various ways. But no one can claim that the relation 

 between p and X is changed, or that other relations between 

 p and X exist, merely because we change our symbols for 



