36 W. & L. E. GURLEY, TROY, NEW YORK 



Tin- details of rating a current meter and of preparing the 

 mrtrr ratini: < m\ and table are given in "River Discharge."* 

 Tin- rating should be done at a rating station, properly equipped 

 to carry on tin- work. The rating station should be allowed 

 ample time-, usually about two weeks, to make the rating and to 

 compute the rating table. The following table gives a list of 

 rating stations and the cost of rating a meter: 



STATION ADDRESS RATING I I 



U. S. Bureau of Standards, Washington, D. C. $10 for each head 



Rensselaer Pol\ tr. lmi<- Institute, Troy, N. Y. $10 for each head 



rester PoKtrrlmir Institute, Worcester, Mass. 

 Cornell University, Ithaca, N. Y. 



University of Michigan, 



Naval Tank, Ann Arbor, Mich. 

 Imperial Valley Development Co., Calexico, Cal. 

 University of Toronto, Toronto, Ontario. 



Irrigation Branch, Department 



of the Interior, Calgary, Alberta. 



Theoretically, the wheel of a differential-action meter, when 

 carried through still water, should revolve as a wheel revolves 

 in passing over the ground. That is, in going a given distance 

 it should make practically the same number of revolutions, 

 regardless of speed. The rating of a great many small Gurley 

 electric meters shows this number to be from 42 to 44 revolu- 

 tions in going 100 ft. 



The true number of revolutions of the wheel should equal 

 the distance of the run divided by the effective circumference 

 of the wheel multiplied by a coefficient which depends on the 

 retarding effect due to the pressure on the convex surface of the 

 cups and their blanketing effect. Assuming the effective cir- 

 cumference to be the circle passing through the points of the 

 cups, which is 0.7854 ft., and the true number of revolutions 

 to be 43/4 per 100 ft. run; then the coefficient would be 0.342. 

 Although complete data are not available to confirm this theory, 

 the working of the meter shows that it holds very closely to it. 



The foregoing shows that the theoretical meter-rating curve 

 is a straight line passing through the origin. If the true num- 

 lirr of revolutions made in going 100 ft. is 43/^2, the equation 

 of this curve will be X = 2.3 Y, where X = velocity, in feet 

 per second, and Y : - revolutions per second. 



" Kiv-r JUsrhnrp-". y Iloyt :ml Gn>V< ULte 1-y W. 4 v I,, ]:. 



c;nrl.-y. 



