time. Many of the original stations have been discontinued be- 

 cause of unfavorable site conditions or other causes. The location 

 and status of each station are shown on Plate 1, entitled "General 

 Locations of Agro climatic Stations, 1954-60." A more detailed de- 

 scription of each of the agroclimatlc stations is presented in 

 Table A-1 of Appendix A. 



Instrumentation at Agroclimatlc Stations 

 Two types of equipment were utilized to measure evapora- 

 tion potential; the Livingston spherical atmometer, and the U. S, 

 VJeather Bureau Standard Class A evaporation pan. U. S. Forest 

 Service precipitation gages, approximately 8 Inches in diameter 

 and 10,5 inches in height, were installed at all agroclimatlc 

 stations at the same elevation above ground as prescribed for a 

 standard U, S, Weather Bureau nonrecording rain gage. Following 

 is a description of evaporation equipment in use and methods of 

 installation. 



A tmo meters 



A Livingston spherical atmometer is a specialized instru- 

 ment used for measurement of evaporation. The atmometer is a hol- 

 low porous porcelain sphere 5 centimeters in diameter. In a typical 

 assembly the sphere is mounted on a 1-gallon water supply bottle 

 by means of a small-diameter glass tube. The sphere and connecting 

 tube ar'e filled with distilled water, with the lower end of the tube 

 extending nearly to the bottom of the reservoir bottle. Thus, there 

 is a continuous water system from the reservoir bottle to the outer 

 surface of the porous sphere, where evaporation takes place. 



