OF FLUID PRESSURE ON THE SIDES AND BASE OF CUBICAL VESSELS. 61 



inches, according to the numbers in the foregoing tablet, and through 

 the remote extremities of the several ordinates, trace the curve line 

 ADC, which will mark the exterior boundary of the section. 



The intelligent reader will readily perceive, that in the actual con- 

 struction of the above figure, it has been found impossible to preserve 

 the proper proportion between the several abscissse and their corre- 

 sponding ordinates ; if this had been attempted, the figure must either 

 have been enlarged to an inconvenient size, or the ordinates would 

 have been so small as to render the general appearance of the section 

 very indistinct. 



We have therefore thought it preferable to preserve the line of the 

 abscissee within moderate bounds, and to enlarge the ordinates in a 

 given constant ratio ; by this means the form of the curve is correct, 

 and the whole diagram is sufficiently distinct for practical illustration. 



In all that has hitherto been done respecting the rectangular 

 parallelogram, we have constantly considered it as being an inde* 

 pendent plane immersed in the fluid, and having its upper side 

 coincident with the surface ; but we must now observe, that whatever 

 relations have been shown to exist on such a supposition, the same 

 will hold, if the plane be considered as the side of a vessel filled with 

 the fluid by which the pressure is propagated. 



We have already alluded to this principle, at the conclusion of our 

 illustration of the fourth problem ; it therefore only remains to deter- 

 mine by it, the pressure on the bottom and sides of a vessel filled with 

 a fluid of uniform density, on the supposition that the bottom and the 

 sides are respectively rectangular planes. 



11. METHOD OF COMPARING THE PRESSURE ON THE PERPENDICULAR 

 SIDES AND ON THE BOTTOM OF ANY RECTANGULAR CISTERN, BASIN, 

 OR CANAL LOCK. 



PROBLEM X. 



75. Suppose that a vessel in form of a rectangular paral- 

 lelopipedon, is filled with fluid of uniform density, and placed 

 with its sides perpendicular to the horizon : 



It is required to compare the pressure on the upright sides 

 with that upon the bottom, both when the sides are all equal, 

 and when the opposite sides only are equal. 



