Frost and the Prevention of Damage bij It. 



23 



these heaters are placed one to a tree. The remainder of the orchard 

 is divided into checks 16 trees square and a double row of heaters 

 is distributed along each check line. The remainder of 3,800 heaters 

 are placed one to each tree in the colder parts of the orchard and 

 one to two trees in the remainder of the orchard. 



"When the time to fire arrives, the direction of the air drift is 

 noted, and the outside row to windward is fired first so that the heat 



One 



_ Two freaterj per free,. 

 Three. footers per free. 



rn;. s. Diagram of 40-acre orange grove owned by Willis S. Jones, near Claremont, 

 Calif., illustrating his system of firing orchard heaters along check lines. Dots repre- 

 sent orango trees, spaced 20 feet apart on the square. Tho normal- direction of the air 

 drift on cold nights is shown by the arrows. 



is carried into the orchard. (See fig. 9.) Three more east and west 

 lines are fired immediately afterwards, and if the temperature con- 

 tinues to fall, three north and south lines are fired. The 40 acres 

 are then divided into 16 checks of 256 trees each, surrounded on all 

 sides except the extreme west and south by lines of fires '20 feet apart. 

 If the temperature still remains low in the colder parts of the orchard, 



