DRIVEN MACHINES 



117 



pletely covered. To do this the pipes are rolled from 

 one side to the other, through a 90 degree arc to throw 

 the spray on both sides. The pipes usually are laid 

 with a grade which follows down the slope of the land. 

 A fall of one foot in fifty is sufficient. Water is always 

 admitted at the upper end of each pipe-line to flow 



25' 



50- 



50' 



SO' Z5' 



Figure 127. Overhead Irrigation. Diagram showing the arrange- 

 ment of pipes for irrigating one acre of land. The pipes are sup- 

 ported on posts six feet high. 



down by gravity, assisted by tank pressure. A pres- 

 sure of about forty pounds is needed to produce a fine 

 spray, and to send it across to meet the opposite jets. 

 The little brass nozzles are drilled with about a one- 

 eighth inch hollow. But the jet opening is small, 

 about No. 20 W. G. This gives a wire-drawn stream 

 that quickly vaporizes when it meets the resistance of 

 the atmosphere. When properly installed a fine misty 

 rain is created, which quickly takes the same tempera- 



