212 LECTURES. 



cylindrical tube as in the circumscribing prism — and hence, in the 

 case of the tube we will have 



1 



1=^- (8.) 



The results in reference to the varying distance of the plates are 

 best exhibited by two squares of glass joined at their vertical edges 

 and opened to an acute angle. The liquid is observed to stand at 

 different points, at heights inversely as the distance of the plates at 

 these points, and therefore its outline must form a hyperbole referred 

 to its asymj) totes. -Proof of this. 



(98.) In the case of two plates of glass plunged into mercury, the 

 depressing force is also found to be constant for each linear unit of the 

 width of the glass parallel to the horizon — consequently the depression 

 must be inversely as the distance of the plates, and twice as great in 

 a tube of the same diameter as the distance of the plates. 



It has been found by experiment that in a glass tube of gV^^^ o^ ^^ 

 inch in diameter the depression is one inch — hence the depression in 

 any other glass tube will be given by 



1 



d' 



%M 



and between two glass plates by (9.) 



1 



d"z=z 



136c? 



(99.) Although the capillary force is constant for the same liquid, 

 it is different for different liquids, as is shown in the following table 

 derived from experiment : 



Water 100 



Solution of common salt 84 



Nitric acid *?5 



Muriatic acid 70 



Alcohol 41 



Purified whale oil • ?>H 



This table exhibits the relative heights of the different liquids in 

 tubes of the same diameter. 



(100.) In the elevation of liquids in tubes the height is the same 

 with the same diameter, whatever may be the substance of which the tube 

 is composed, but in the case of depression the depressing force varies 

 with the substance of the tube as well as with the diameter. Expla- 

 nation of this. 



(101.) The elevation of liquids is readily explained in its general 

 features, on the principle we have already given of the adhesion of 

 the liquid to the solid and the cohesion of the liquid to itself; but to 

 explain the depression and a number of other facts connected with the 

 subject require something more. 



