juiyjo, I9I7 Evaporation from Water and River-Bed Materials 213 



this discussion. The number is given, together with the description, in 

 Table I. All tanks are galvanized metal. The location of each is shown 

 in figure 2. 



Tabi.B I. — Description of pans used in evaporation studies 



Throughout the work actual measurements of evaporation were made 

 by hook gage, observations being to the water surface ^vith the hook 

 gauge set at the definite and fixed datum on the rim of the tank. The 

 type of gage used is that developed by E. J. Hoff, of this Ofiice, 

 for evaporation work (24) and is shown in Plate 34, A . But two gages 

 were used throughout the progress of all the measurements, one of them 

 kept for use with tank 9 (floating) and the other for use at the labora- 



