HYDRAULICS. 197 



287. The time that a cylindric vessel, (the area 

 of its base being i 2 ), requires to empty itself by a 

 hole in the bottom, of which the area is a 2 , the 

 depth at the beginning of this discharge being 



j ? j s J ; and the time that the surface takes 



to sink, from the depth d to any other depth d', is 



DAN. BERXOUILLJ, Hydrodynamica, sect. iv. 13. ; 

 BOSSUT, Hydrodyn. torn. i. 232. 



The construction of the clepsydra, or water-clock, de- 

 pends on this proposition. If the whole depth 

 through which the surface of the water sinks in 12 

 hours be divided into 144 parts, it will sink through 

 23 of these in the first hour, 21 in the second, 19 in 

 the third, and so on, according to the series of the 

 odd numbers. 



288. The vein of water, as it issues out, is con- 

 tracted ; and from that, and other causes, the actual 

 discharge of water is not so great as it is computed 

 to be in the foregoing theorems. This difference, 

 however, affects only the absolute quantities, and 

 not their proportions ; the quantities really dischar- 

 ged 



