Journal of Agricultural Research 



The results of this comparison are given in Table III, which shows that 

 the second method of computation gives the more accurate results. In 

 no class of canal section does either three-point method give as accurate 

 average results as the 0.2 and 0.8 depth method alone. In the individual 



experiments in one-seventh of the total number the — '- '— 



method gave more accurate results than the 0.2 and 0.8 depth alone. 



In one-fifth of the total number the 



0.8-1-0.6 



method gave results 



more accurate than the 0.2 and 0.8 depth alone. These were for gagings 

 in which the errors of the 0.2 and 0.8 depth method were of different 

 sign from those of the 0.6 method, so that their combination reduced the 

 actual error. These cases were generally for canals of irregular section 

 and flow, and indicate that for unfavorable conditions of current-meter 

 work the three-point method may be preferable to the two-point, but 

 that for usual conditions the two-point alone is preferable. However, 

 under unfavorable conditions of irregular velocity and cross section only 

 detail multiple-point obser^^ations can be depended upon for accurate 



results. The 



of the results to the 



0.2 + 0.8+0.6 

 3 



0.2+0.5 



method is always preferable for computation 



;+2 X0.6 



method. 



Table III. — Variation in discharge in percentage by the three-point method compared 

 with the multiple-point method 



MEASUREMENTS WITH SURFACE FLOATS 



In many experiments measurements with surface floats were made in 

 order to secure data f I'ora which the proper coefficients for use with such 

 measurements could be derived. It is often convenient to make such 

 approximate measurements by timing floats over a known length of 

 canal and applying some coefficient to the product of the velocity so 



