THE WATER HAM. jOj. 



by the height it passes through, and the product of these tvi^o 

 numbers is the expression of the power. Thus I may kiiow 

 with precision the quantity of the power I have at my dis- 

 posal. 



As I give the name of power to the product of the mass of Author's u:;* of 

 ,.,.,, , , . , r • ,^ 11 r 1-. • ■ 1 the terms poicef 

 water multiphcd by the height of its fall, 1 likewise giye tlic ^nd effect. 



name of cft'oct to the product of the mass of water raised, 

 multiplied by the height to which it is carried. This is the 

 cfibct or useful product of the machine. 



This second quantity can never be equal to the first, because The effect is 

 in the motion oi the machine a part of the poiver is ^.Iways "^^^""^^^ J^ , 

 expended [in generating velocity, and] in overcoming friction, duciiig it. 

 ind in useless movements : but we may bring them considera- 

 I'ly nearer to an equality, by diminishing, as much as possible, 

 ■-?, last two impediments of which I have been speaking, and 

 ■ IS I have in part cftectcd in the water ram. 



Thus to estimate the value of a machine, we must find the Ground of the 

 ratio of the power expended, or of the mass of water that falls e3atf!>7 

 multiplied by the height of the fall, to the effect produced, or machines, 

 the mass of water raised multiplied by the height of its ascent. 

 The comparison of these two quantities gives the true mea- 

 sure of Ihe c-xcelieuce of the machine. 



will be sufficient ro measure the aperture, and the height from the 

 midiie of the aperture to the surface of the water. By multiply-r 

 ins;, tiie surface of tlie aperture by the velocit}^ the water would 

 acquire in falling from the surface to the middle of the aperture, 

 and takint^ two-thirds ot the product, wc shall have nearly the 

 quantity discharged. Tf we had a brook or a rivulet to measure 

 where there was no full, we may observe the height to which the 

 water would rise against an obstacle opposed to the stream, such 

 as a slip of wood two inches wide and half an iuch thick, and cal- 

 culating the velocity as in the preceding case, multiplying it by the 

 surface of a section of the river perpendicular to the current^, and 

 this would give the mass of the flowing water. 



The velocity of the water may also be better estimated by that of 

 any floating body, following it a little time with a watch in the 

 liand. If we have a small spring to measure, and a reservoir at 

 our disposal, it would be a much more certam method to calcu- 

 late the capacity of the reservoir, and observe the time it took to 

 ftU. (Tlwise last give rough estimates only. N.) 



The 



