[farmer] determination OF COEFFICIENT OF DISCHARGE 



59 



From each of these curves four dilferent vanes are derived. These 

 were got by cutting off the surfaces at sections distant approximately 1^, 

 3, 4^ and 6 inches from the apex of the curve. The total angles through 

 which the water was turned before leaving the vane was in the several cases : 



Vane I. Ih" deep 

 Vane II. 3" " 

 Vane III. U" " 

 Vane IV. 6" " 



Circular 

 Section. 



132^=" 

 151' 

 166 

 180" 



Elliptic 

 Section. 



134i^ 

 1491° 

 154r 

 lo9h° 



Parabolic 

 Section. 



134i" 

 145^° 

 149 

 152? 



It will be noticed that the relative sizes of the vanes and of the im- 

 pinging jets differed very considerably from those met with in practice. 

 The etfect due to friction was therefore very much exaggerated under the 

 conditions obtaining in these experiments. Assuming that the water 

 passed over the vane without being broken up, if the final velocity were 

 equal to the initial, this would mean in some cases that the water would 



$0' 40" SO* 

 /fSAO 20 feer 



Diagram VI. 

 only form a sheet -005" thick on the surface of the vane. The frictional 

 resistance on water moving with a considerable velocity under such cir- 

 cumstances must be enormous and in the experiment it could be seen that 

 the etfect was to greatly reduce, and in some cases almost entirely destroy 

 the initial velocity. 



In the following table the coetftcients for flat plates are included for 

 the sake of comparison. The coefficients in this table are those based on 

 the total force acting under the conditions of the experiments ; no attempt 

 was made as in the previous tables, to eliminate the effect of gravity or 

 other ettects, which must be small compared with the total amount. 



