168 COEFFICIENT OF RESISTANCE. 



But, from (1) of Art 93, 



V 



4>' 

 which in (3) gives 



stored work lost = ( -, 1 ) W. (4) 



\(fr 1 2g 



This loss of stored work corresponds to the head of water 







which we can therefore consider as the loss of head due to 

 the resistance of efflux, and we can assume that, when this 

 loss has been subtracted, the remaining portion of the head 

 is employed in producing the velocity. 



The loss of head in (5), which varies as the square of the 

 velocity, is known as the height of resistance. 



1 v 3 



The coefficient 1, by which the head of water - 



V fy 



must be multiplied in order to obtain the height of resist- 

 ance, i. e. } the ratio of the height of resistance to the head 

 of water, is called the Coefficient of Resistance. 



COR. 1. Denote the coefficient of resistance by ft- then 

 we have 



* = -!, (6) 



which in (5), and denoting the loss of head or the height of 

 resistance by z, we have 



. = * (7) 



COR. 2. For efflux through well-formed smooth orifices 

 in a thin plate, the mean value of = the mean of .96 and 

 .99 (Art. 93), = 0.975, and therefore we have, from (6), 



