IRRIGATION 83 



The greater the pressure tjie finer the spray ; but after 

 reaching a certain pressure the spray is so fine that it 

 retards the flow of water and reduces the distance of 

 throw. It follows that when the pressure is so high as 

 to produce these results, the lines must be installed 

 slightly closer together, according to the preceding table. 

 The above pressure refers to pressure at nozzles. 



FIG. 1 8. IRRIGATION SYSTEM INSTALLED AT THE 

 PENNSYLVANIA STATE COLLEGE 



Figure 18 shows the overhead system in use at the 

 Pennsylvania State College. A lever is provided at one 

 end of each nozzle line, by means of which the entire line 

 is easily turned. When in operation, the line is kept in 

 one position until a strip of land has been sufficiently 

 watered, and then the line is turned so the spray will fall 

 on unwatered ground. It takes only a few seconds to 

 turn each line and the attendant may be engaged in other 



