1844] WRITINGS OP JOSEPH HENRY. 217 



ON THE COHESION OF LIQUIDS. 



(Proceedings of the American Philosophical Society, vol. iv, pp. 56, 57.) 



Ap?-U 5, 1844. 



Professor Henry made a verbal communication relative to 

 " the cohesion of liquids." 



He stated that very erroneous ideas are given as to the 

 constitution of matter in the ordinary'' books on Natural 

 Philosoph3^ The passage of a body from a solid to a liquid 

 state is generally attributed to the neutralization of the 

 attraction of cohesion by the repulsion of the increased 

 quantity of heat, the liquid being supposed to retain a small 

 portion of its original attraction, which is shown by the 

 force necessary to separate a surface of water from water, in 

 the well known experiment of a plate suspended from a scale 

 beam over a vessel of the liquid. It is however more in 

 accordance with all the phenomena of cohesion to suppose, 

 instead of the attraction of the liquid being neutralized by 

 the heat, that the effect of this agent is merely to neutralize 

 the polarity of the molecules so as to give them perfect free- 

 dom of motion around every imaginable axis. The small 

 amount of cohesion (53 grains to the square inch) exhibited 

 in the foregoing experiment, is due, according to the theory 

 of capillarity of Young and Poisson, to the tension of the 

 exterior film of the surface of water drawn up by the eleva- 

 tion of the plate. This film gives way first, and the strain 

 is thrown on an inner film, which in turn is ruptured, and 

 so on until the plate is entirely separated, the whole effect 

 being similar to that of tearing water apart atom by atom. 



Reflecting on this subject, he had thought that a more 

 correct idea of the magnitude of the molecular attraction 

 might be obtained by studying the tenacity of a more 

 viscid liquid than water. For this purpose he had recourse 

 to soap-water, and attempted to measure the tenacity of this 

 liquid by means of weighing the quantity of water which 

 adhered to a bubble of this substance just before it burst, 

 and by determining the thickness of the film from an obser- 



