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 not as might at first 

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

 mobility of the molecules." In fact the actual tenacity of pure water 

 is greater than that of soap-water. 



The first set of experiments was directed to determine "the 

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

 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 filled with water, by the barometric column sustained in 

 the narrower stem of the tube; the difference of level being 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 bursting. 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 force of 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 Nat. Philos. Lect. 50, vol. i. p. 627. 



f"If we attempt to draw up from the surface of water a circular disk of metal 

 say of an inch in diameter, we shall see that the water will adhere and be supported 

 several lines above the general surface. This experiment which is frequently given 

 in elementary books as a measure of the feeble attraction of water for itself, is im- 

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

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

 (Agricultural Report for 1857. p. 427. Henry's paper on Meteorology.) 



J Proceed. Am. Phil. Soc. April 5 and May 17, 1844, vol. iv. pp. 56, 57, and 84, 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 fire in 1865. 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 degree of cohesion. On the contrary, the 

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



