THE PEAIEIES 



201 



The relative humidity of the air varied at the several stations 

 as indicated in the followinsr table : 



The psyehrometer record for August 13tli is incomplete, and is 

 omitted. 



The foregoing results sho^v clearly that evaporation is much 

 more rapid in the exposed prairie areas than from areas protected 

 by topography or forest. 



The relation which meteorological conditions, influenced by to- 

 pography, bear to evaporation is well illustrated by the results 

 which were obtained at station 1 and represented in part graph- 

 ically in plates XII and XIII. Each of the figures on these 

 plates presents three curves : The full line (A) represents the 

 amount of evaporation from a Piche evaporimeter, measured in 

 tenths of a cubic inch, the latter forming the ordinates of the 

 curve; the broken line (B) represents the velocity of the wind in 

 miles per hour, the latter forming the ordinates of the curve ; 

 and the dotted line (C) represents the temperature in Fahren- 

 heit degrees, the latter also forming the ordinates of the curve. 



In all cases the hours of the day between 7 o'clock A. M. and 

 7 o'clock P. 'M. form the abscissas of the curves, each space rep- 

 resenting one hour. 



VOL VI — 1. 15 



