Evaporation Is determined by measuring the amount of water re- 

 quired to refill the reservoir bottle to a reference mark. A 

 typical atmometer assembly Is shown on Figure 1, 



Atmometers are operated as pairs consistlnc of one 

 white and one black sphere set 15 Inches apart and ^4 Inches 

 above ground surface. Prior to 1958^ many installations had only 

 a single pair of atmometers; however, since that time three or 

 more pairs of atmometers have been Installed at each of the sta- 

 tions included in the monitoring program. 



Evaporation Pans 



U, S. Weather Bureau Standard Class A evaporation pans 

 were adopted in the agroclimatic program in 1937 and installed 

 at certain of the stations. The pans were installed in accordance 

 with the procedure prescribed in "instructions for Climatological 

 Observers," Circular B. Tenth Edition, Revised October 1955, U. S. 

 Department of Commerce. 



All stations included in the Agroclimatic Monitoring 

 Program are periodically inspected to ascertain that equipment 

 is correctly installed and properly exposed. Complete records 

 for all stations are available in the files of the department. 

 Typical agroclimatic station installations are shown in Figure 2. 



Agroclimatic Data Analysis 

 Summaries of the agroclimatic data collected during the 

 period from July 195^ through December 196O are shown in Tables 1 

 and 2. Table 1 shov;s the means of monthly evaporation from standard 



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