490 Albert P. Mathews 



clearly the reason which led him to the conclusion that molecu- 

 lar cohesion penetrated matter like gravitation, and that the 

 attraction must, hence, decrease very rapidly with the dis- 

 tance. It will be seen that the sole reason for his decision 

 was the possible analogy between gravitation and molecular 

 cohesion. 



The very important result of the rejection by Laplace 

 of the possibility of cohesive attraction not penetrating matter 

 was that it forced him to the conclusion that the cohesive 

 force must diminish far more rapidly than gravitation as the 

 distance increases. Laplace did not make any assumption 

 as to the rate at which the cohesional attraction diminished 

 with the distance, except that it was at so rapid a rate that 

 the cohesion became negligible within all measurable dis- 

 tances. 



The great English philosopher, Thomas Young, 1 who 

 a year before Laplace had shown the true nature of surface 

 tension and practically anticipated all of Laplace's main 

 conclusions, does not appear to have raised the question in 

 a concrete form. His papers on capillarity are so condensed 

 that the reasoning is very difficult to follow. 2 



But while Young nowhere specifically puts the question 

 whether the cohesional attraction penetrates matter, he 

 made an assumption which might be taken to indicate that 

 it does not. "We may suppose," he says (p. 43), "the parti- 

 cles of liquids, and probably those of solids also, to possess 

 that power of repulsion which has been demonstratively 

 shown by Newton to exist in aeriform fluids, and which varies 

 as the simple inverse ratio of the distance of the particles 

 from each other. In air and vapors this force appears to act 



1 Young: "An Essay on the Cohesion of Fluids," Phil. Trans., 1805 

 (collected works, edited by G. Peacock, i, 418 (1855), London). 



2 A propos of this paper of Young's, Clerk Maxwell makes an interesting 

 comment. He says: "His [Young's] essay contains the solution of a great 

 number of cases including most of those afterwards solved by Laplace; but his 

 methods of demonstration, though always correct and often extremely elegant, 

 are sometimes rendered obscure by his scrupulous avoidance of mathematical 

 symbols." Ency. Brit., Article, "Capillarity." 



