juiy3o, 191 7 Evaporation from Water and River -Bed Materials 229 



The figures show that for the first set of tanks evaporation from the 

 flowing water was 107 per cent of that from the still water under exactly 

 the same conditions. For the other set, a tank 25 feet long, the evapo- 

 ration from the flowing water was 108 per cent of that from still water. 

 While this experiment was limited because of the low water velocity, 

 it would tend to show that evaporation loss from a canal would be slightly 

 greater than from a still body of water under exactly the same conditions 



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16 



Fig. 5. — Relation of evaporation and temperature, all other factors being similar. 



of exposure, temperature of water, etc. There seems to be no definite 

 relation between evaporation and velocity within the limits of the 

 experiment. 



The only previous work in this connection noted is that carried out 

 in Spain in 1849 (4), which for the short period of the experiment indi- 

 cated an evaporation from moving water, agitated but not flowing, 

 of 140 per cent of that from still water. Temperature effect was not 

 considered in this, so far as can be learned. 



