Frost and the Prevention of Damage by It. 



21 



The plan of using small oil heaters which burn slowly and setting 

 them directly under the trees has not met with much success up to 

 the present time. There is always danger of severely injuring the 

 tree if the heater burns too high, and the problem of distributing the 

 heat uniformly throughout the tree has not yet been solved. 



Protection by Direct Radiation From Heaters. Though protec- 

 tion from frost is afforded mainly through raising the temperature 

 of the air by mixing with the hot gases from the heaters, direct 



FIG. 7. Two types of high-stack oil heaters. Air is admitted through a draft opening 

 in the cover of the bowl, supporting combustion at the surface of the oil. The hot 

 gases then burn while rising through the stack, the necessary air being admitted 

 through the perforations near the base. At the left of the heater on the right is 

 shown a lighting torch of the type in most general use. It consists of an ordinary 

 oil can with a long spout, into the end of which is inserted a wick of asbestos 

 wrapped in small mesh wire screen. The lighting fluid is ignited while flowing 

 through and around the wick and falls in flaming drops. 



radiation of heat to the plants or trees is important in some cases. 

 This is particularly true when the high-stack heaters are used. When 

 these are burned at a moderate rate at least a portion of the stack is 

 likely to be heated to redness. The heat radiated from the stack to 

 the fruit and foliage serves to counterbalance the loss of heat through 

 outgoing radiation. The amount of radiant heat reaching the tree 



