218 WRITINGS OF JOSEPH HENRY. [1844 



vation of the color it exhibited in comparison with Newton's 

 scale of thin plates. Although experiments of this kind 

 could only furnish approximate results, yet they showed that 

 the molecular attraction of water for water, instead of being 

 only about 53 grains to the square inch, is really several 

 hundred pounds, and is probably equal to that of the attrac- 

 tion between the molecules of ice. The effect of dissolving 

 the soap in the water is not (as might at first appear,) to 

 increase the molecular attraction, but to diminish the mo- 

 bility of the molecules, and thus to render the liquid more 

 viscid. 



ON THE COHESION OF LIQUIDS. (CONTINUED.) 



(Proceedings of the American Philosophical Society, vol. iv, pp. 84, 85.) 

 May 17, 1844. 



Professor Henry made a second communication on the 

 subject of cohesion. 



He had prosecuted his experiments on the soap-bubble to a 

 further extent, and had arrived at a number of results which 

 appeared to him of some interest in reference to capillarity, 

 a subject which had given rise to a greater diversity of 

 opinion than any other part of natural philosophy. As an 

 evidence of its present unsettled state, he mentioned the fact 

 that the last edition of the Encydopoedia Britannica con- 

 tained two articles on this subject under different names; 

 one by Dr. Young, and the other by Mr. Ivory, which ex- 

 plain the phenomena on entirely different physical prin- 

 ciples. 



According to the theory of Young and Poisson, many of 

 the phenomena of liquid cohesion, and all those of capillar- 

 ity, are due to a contractile force existing at the free surface 

 of the liquid, and which tends in all cases to urge the liquid 

 in the direction of the radius of curvature towards the 

 centre, with a force inversely as this radius. According to 

 this theory the spherical form of a dew drop is not the effect 

 of the attraction of each molecule of the water on every 



