64 



HYDROLOGY 



culated from careful soundings and the mean velocity ascertained 

 by making measurements at different depths. By multiplying 

 the area and the velocity for each strip, its discharge value is 

 determined independently of the other, and by adding them 

 together the total is arrived at in the most accurate manner. 



Of: 



FIG. 23. Price Electric Current Meter with Telephone Sounder, 

 factured by W. & L. E. Gurley, Troy, N. Y.) 



(Manu- 



The greatest error in these estimates is generally due to inac- 

 curate determination of the mean daily gauge heights, ordinarily 

 secured from a few observations during the day or even more 

 infrequently. This has led to the introduction of automatic 

 water stage registers (see page 265), by which the varying height 

 of water may be accurately gauged and a dependable, continuous 

 record obtained. 



