Relationship between Molecular Cohesion 497 



range of cohesive action must be of the general value of, 

 and proportional to, the distance between the molecular 

 centers. This distance is of the order of magnitude in most 

 liquids of io~ 8 cm. This result is so surprising that Einstein 

 says of it: "This result appears at first very unlikely, for 

 what should the radius of action of a molecule have to do with 

 the distance between neighboring molecules? The supposi- 

 tion is only reasonable in case the neighboring molecules alone 

 attract each other, but not those farther removed. " 



Sutherland 1 also came to the conclusion that the radius of 

 action was about equal to 7/ /3 . We see then, that the evi- 

 dence points to the conclusion that the radius of action of 

 the molecular forces agrees very closely with -z/ /3 , the distance 

 between the molecular centers, and varies directly with T/ /3 . 

 The only explanation of this fact appears to me to be that the 

 attraction does not extend beyond neighboring molecules 

 and, hence, must, in some way, be stopped by them. 



Mills 2 alone, so far as I can find, has reopened the question 

 whether the field is delimited by the surrounding molecules. 

 Concluding, I believe erroneously, from an empirical law, 

 that the attraction between molecules must vary inversely 

 as the square of the distance, he was driven to the second 

 conclusion that if this were the case the cohesion could not 

 penetrate matter. He assumed, hence, that the surrounding 

 molecules absorbed, or neutralized, the lines of cohesive force. 

 The direct evidence and Einstein's reasoning leaves little 

 doubt that the radius varies with the distance apart of the 

 molecules and the only possible conclusion from this is that 

 the surrounding molecules delimit the field as Mills supposes. 

 If it is a fact that the surrounding molecules delimit the 

 field as the evidence indicates, cohesion is allied at once with 

 magnetism, foi" this is the very supposition which Ewing 

 made to explain some of the phenomena of magnetism. Each 

 molecule of a ferromagnetic substance is supposed to be a 



1 Sutherland: Phil. Mag., [6] 4, 632, 636 (1902). 



2 Mills: Jour. Phys. Chem., 15, 417 (1911). 



