io8 



RELATIONS OF SOIL TO WATER 



from soil is to consider in the first place the simpler case of 

 the evaporation from a water-surface. Greaves (Proc. fnstit. 

 Civil Engineers, Feb. 29, 1876) has determined for many years 

 the evaporation from a tank having one square yard of sur- 

 face ; the tank was kept floating in a stream of water, the 

 temperature of the water in the tank was thus similar to that 

 of the bulk of water surrounding it. The average amounts of 

 evaporation he observed were as follows : 



TABLE XVIH 



EVAPORATION FKOM A WATER SURFACE NEAR LONDON. 

 AVERAGE OF FOURTEEN YEARS (GREAVES) 



We see that the average amount of evaporation from the 

 water-surface has been 20-66 inches in the year. The rate of 

 evaporation is very different in the different seasons. From 

 November to February the evaporation is only 0-6-0-7 inch 

 per month. After February a rapid rise sets in, the largest 



