REPORT ON CAPILLARY ATTRACTION. S57 



Hauksbee records an experiment by wliich it appears that if 

 a large tube of glass be closely filled with ashes, and one end be 

 dipped in water, in the space of a week or fortnight the water 

 will rise within the tube to 30 or 40 inches above the level of 

 the water without. Newton, in noticing this experiment, says 

 correctly, that the rise is owing " to the action only of those 

 particles of the ashes which are upon the surface of the elevated 

 water, the particles which are within the water attracting or re- 

 pelling it as much downwards as upwards." 



Another experiment by Hauksbee shows that a drop of wa- 

 ter inserted between two plates inclined to each other at a very 

 small angle, and touching at their edges, is attracted to the junc- 

 tion of the edges by a force varying inversely as the square of 

 the distance from it. Newton attempts to account for this phae- 

 nomenon, but unsuccessfully. The true explanation was reserved 

 for Dr. Young and Laplace. 



When two planes inclined at a small angle are immersed in 

 water, with the line of their junction vertical, the outliYie of the 

 water that rises between them is on each plane nearly an hyper- 

 bola, of which the asymptotes are the line of intersection of the 

 plane with the horizontal surface of the fluid, and the line of 

 junction of the two planes. Taylor first ascertained this by 

 measurement*. It is a simple consequence of the law accounted 

 for by Newton, of the rise of water between parallel planes to a 

 height inversely proportional to the interval between them ; for 

 the planes being inclined at a very small angle, opposite elements 

 of them may be considered parallel. 



The early theories of capillary attraction were defective in two 

 respects : they contained no calculation founded on the hypo- 

 thesis of an attraction sensible only at insensible distances from 

 the attracting centres, although the existence of such forces was 

 already recognised, and Newton had given an example of calcu- 

 lation made with reference to force of this nature in the instance 

 of the passage of light through a dense medium ; and they took 

 no account of the cohesive attraction of the parts of the fluid 

 for each other. The necessity of considering the mutual at- 

 traction of the particles of the fluid would seem to be very evi- 

 dent when once the law of attraction, sensible only at insensible 

 distances, was admitted; for supposing the capillary tube to 

 attract only the fluid particles at insensible distances from its 

 surface, a column of water of sensible breadth could not be 

 suspended except by the intervention of a cohesive power resi- 



* Philosophical Transactions, 1712, No. 336, p. 538. 

 1834. s 



