DISCOURSE OF W. B. TAYLOR. 265 



pression is found by experiment to differ very little from that of 

 water contained in a vessel,"* all the most popular text-books on 



physics continued to teach that the cohesion of the liquid state is 

 intermediate between that of the solid and the gaseous states. f It 

 seemed therefore desirable to test the question by some more direct 

 means than the resistance of liquids contained in closed vessels : and 

 for this purpose Henry employed the classical soap-bubble. ''The 

 effect of dissolving the soap in the water is nut a- might at first 

 appear, to increase the molecular attraction, lint to diminish the 

 mobility of the molecule.-." In fact the actual tenacity of pure wat< 1 

 is greater than that of soap- water. 



Tlie first -et of experiments was directed to determine "the 

 quantity of water which adhered to a bubble just before it hurst." 

 The second set of experiments was devised to measure the contractile 

 force of a soap-bubble blown on the wider end of a U-shaped glass 

 tube half tilled with water, by the barometric column sustained in 

 the narrower stem of the tube; the difference of level beine care- 

 fully observed by means of a microscope. The thickness of the 

 soap-bubble film at its top was estimated by the last of the Newton 

 rings shown previous to bur-ting. The result arrived at from both 

 sets of experiments was that water instead of having a cohesion of 

 53 grains to the square inch (as was very commonly stated), has a 



cohesive for )f several hundred pounds to the inch; or that the 



inter-molecular cohesion of a liquid is fully equal to that of the sub- 

 stance in the solid state. J 



'Young's Lectures on UTaLPhilos, Lect.50, vol. i. p. 627. 



t ■' If we attempt to draw up from the surface of water a circular disk of metal 

 saj "fail inch in diameter, we shall see that the water will adhere and be supported 

 several lines above the _•. w ral surface. This experiment which is frequently given 

 In elementary I ks as a measure of the feeble attraction of water for itself, !> im- 

 properly interpreted. It merely indicates the force of attraction of a single tilm of 

 atoms around the perpendicular surface, and not of the whole column elevated." 

 (Agricultural Report for 1^,7. p. 127.— Henry's paper on Meteorology.) 



XProcer<!. Am. Phil. Soc. April 5 and May 17, ISM, vol. iv. pp. 58, .".7. and si. 85. The 

 original notes of these interesting experiments containing the numerical results 

 obtained under a great variety of conditions, laid aside for further reductions and 

 comparisons, were destroyed by tire in 1S65. since the density of most solid sub- 

 stances differs very slightly from that of their liquid state, being indeed less In 

 many, — unless at considerably lower temperatures, (as in the case of ice, and most 

 of the metals, it appears quite- improbable that the difference between solidity and 



liquidity could depend in any case on the degr f cohesion, i m tin ntrary, the 



cohesion of water should be sensibly greater than that of ice, since its constituent 



