COHESION OF FLUIDS, "^O 



tn the case of the elevation of a fluid in contact with a hori- Application of 



zontal surface, tlve ordinate may be determined from the *'^'-' ^o<^tn«fi it<^ 



'' particular > 



weight required to produce a separation ; and the appropriate fluids. y;.^,,ii 



rectangle may be found in this manner also, the angle of con- • : 



tact being properly considered, in this as well as in the former 

 case. It will appear that these experiments by no means ex- 

 hibit an immediate measure of the mutual attraction of the 

 solid and fluid, as some authors have supposed. 



Sir Isaac Newton asserts, in his Queries, that water ascends 

 between two plates of glass at the distance of one hundredth 

 of an inch, to the height of about one inch ; the product of 

 the distance and the height being about .01 ; but this appears 

 to be much too littk. In the best experiment of Mussehen' 

 broek, with a tube, half of the product was .0195; in several 

 of Weitbrecht, apparently very accurate, 0214. In Monge's 

 experiments on plates, the product was 2.6 or 2.7 lines, about 

 ,0210, Mr. Atu'ood says that for tubes, the product is .0530, 

 half of which is .0265. Untill more accurate experiments 

 :jhail have been made, we may be contented to assunw .02 

 for the rectangle appropriate to water, and .O* for the pro- 

 duct of the height in a tube by its bore. Hence, when the 

 curve becomes infinite, its greatest ordinate is .2, and the height 

 of the vertical portion, or the height of ascent against a 

 single vertical plane .14, or nearly one-seventh ofan inch. 



Now when a horizontal surface is raised from a vessel of 

 vater, the surfac^e of the water is formed into a lintearia to 

 %\hich the solid is a tangent at its highest point, and if the solid 

 be still further raised, the water will separate: the surface vof 

 the water, being horizontal at the point of contact, cannot^dd 

 to the weight tending to depress the solid, which is therefore 

 simply the hydrostatic pressure of a column of water equal 

 in height to the elevation, in this case one-fifth of an inch, 

 and standing on the given surface. The weight of such a 

 column will be 50 grains and a half for each square inch ; and 

 in Taylor's well known experiment the weight required was 

 59 grains. But when the solid employed is small, the curva* 

 ture of the horizontal section of the water, which is convex 

 i^xternally, will tend to counteract the vertical curvature, and 

 to diminish the hoight of separation ; thus if a disc of an inch 

 in diameter were employed, the curvature in this direction 



would 



