EVAPORATION AND PLANT DEVELOPMENT. 



271 



The atmometer used in these studies was a modifica- 

 tion of the instrument described in Publication No. 50 of the 

 Carnegie Institution- It consists essentially of an exposed 

 porous clay cup connected with a reservoir at a lower level. 

 The cup is about thirteen centimeters long by two and a half 

 centimeters in diameter, closed and rounded at one end, and 



Figure 54. Sketch showing the arrangement of the parts of the new instru- 

 ment for measuring evaporation. 



reinforced at the other by a thickened rim. The wall is 

 about four millimeters in thickness. The open end is closed 

 by means of a perforated rubber stopper bearing a glass 

 tube some thirty centimeters in length, which extends through 



