OF FLUID PRESSURE ON THE SIDES AND BASE OF CUBICAL VESSELS. 63 



Consequently, when all the four sides of the rectangular vessel are 

 equal to one another, 



The total pressure on the upright surface, is to the 

 pressure on the bottom, as twice the length of the side is to 

 its breadth. 



Again, when all the sides of the vessel have the same breadth, and 

 the length I equal to the breadth b ; then, the vessel becomes a cube, 

 and the total pressure on the upright surface, is 



P=26 3 s, 



and that on the bottom, is 

 p = b 9 s ; 



therefore, by analogy, we obtain 



P :p :: 2 : 1. 



Hence it appears, that when the vessel is a cube, that is, when the 

 bottom and the four upright sides are equal to one another, 



The total pressure upon the four sides, is to the pressure on 

 the bottom, in the ratio of 2 to 1 . 



Since the pressure on the upright surface of a cubical vessel, is 

 double the pressure on the base ; it follows, that the entire pressure 

 which the vessel sustains, is equal to three times the pressure upon its 

 bottom ; that is, 



P+p=:'3b*s. (32). 



But the expression b*s is manifestly equal to the weight of the 

 fluid ; consequently, the total pressure upon the sides and base of 

 the vessel, 



Is equal to three times the weight of the fluid which it 

 contains. 



Now, in the case of water, where the specific gravity is represented 

 by unity, the equation marked (32) becomes 



P+p = 3b*; 



but when the dimensions of the vessel are estimated in feet, and 

 the pressure expressed in pounds avoirdupois, of which 62| are equal 

 to the weight of one cubic foot of water ; then, the above equation is 

 transformed into 



p' = 187.56 s . (33). 



COROL. This equation in its present form implies, that if the solid 

 content of the vessel in cubic feet, be multiplied by the constant 



