COHESION OF FLUIDS. 159- 



Ae difference between the cosme and the radius, or by half tne Cohesire at- 

 versed sine^ or, it the force of the fluid be represented by the s||i^|l*" ^^^ 

 diameter, the whole versed sine will indicate the force of the iiuids, 

 solid. And the safne result foHows when the angle of tire fluid 

 is acute. Hence we may infer, that if the solid have half the 

 attractive force "of the fluid, the surfaces will be perpendicular ; 

 and this seems in itself reasonable, since two rectangular edges 

 of the solid arc equally near to the angular particles with one of 

 the fluid, and we may expect a fluid to rise and adhere to 

 the surface of every solid more than half as attractive as itself: 

 a conclusion which Clairaut has already inferred, in a diilerent 

 manner, from principles which he has but cursoril}^ investiga- 

 ted, in his trea-tjse on the figure of the earth. 



The versed sine varies as the square of the sine of half the 

 angle : the force must therefore be as the square of the height 

 to which the fluid may be elevated in contact with a horizontal 

 surface, or nearly as the square of the number of grains ex- 

 pressing the apparent cohesion. Thus, according to the expe- 

 riments of IMorveau, on the suppositions already premised, 

 wc may infer that the mutual attraction of the particles of 

 p.iercuiy being unity, that of mercury for gold will be .1 or 

 more, that of silver about .94, of tin .90, of lead .81, of bis- 

 muth .72, of zinc .21, of copper 10, of antimony .08, of iron 

 .07, and of cobalt .0004. The attracti^m of glass for mercury 

 will be about one-sixth of the mutual attraction of the par- 

 ticles of mercury ; but when the contact is perfect, it appears 

 10 be considerably greater. 



Although the v;hole of this reasoning on the attraction of 

 solids is to be considered rather as an approximation than as a 

 .strict demonstration, yet we are amply justified in concluding, 

 that all the phenomena of capillary action may be accurately 

 explained and mathematically demonstrated from the general 

 law of the equable tension of the surface of a fluid, together 

 with the consideration of the angle of contact appropriate to 

 every combination of a fluid with a Svolid. Some anomalies, 

 noticed by Musschenbroek and others, respecting in particu- 

 lar the effects of tubes of considerable lengtlis, have not been 

 considered : but there is great reason to suppose that eitlier 

 the want oi uniformity in the bore, or some similar inaccuracy, 

 has been the cause of these irregularities, which have by ny 



means 



