A Consideration of Adcerse Temperatures 333 



It has been determined by O'Gara' that a lard-pail type 

 of heater having a working capacity of about 5 quarts of oil 

 (full capacity 1^ gallons) and a surface area of about 45 

 square inches at the top, will consume oil at the rate of about 

 12^ gallons to the acre an hour when used at the rate of 50 

 heaters to the acre, and that where it is practically still with 

 the wind moving not more than one or two miles an hour 

 and where the trees are of sufficient size to cover much of the 

 ground in the spread of the branches, the quantity of oil 

 stated (12^ gallons to the acre) will raise the temperature 

 4 to 5 degrees. Where the trees are smaller and the heat 

 escapes between them more freely or where the wind is 

 moving more rapidly, a correspondingly larger number of 

 heaters must be used and more oil must be consumed in a 

 given period of time in order to maintain a given temperature. 

 A rise of 3 to 5 degrees of temperature in an orchard using 50 

 to 100 heaters is generally about the limit, except under very 

 favorable conditions, though instances have been reported 

 in which the temperature inside an orchard was maintained 

 at a point 10 degrees higher than on the outside. 



For effective heating, it is necessary to provide some 

 surplus in oil-pots as a margin of safety. This is the case 

 especially since by the time about one-half the contents of 

 the pots have been burned the oil is being consumed only 

 about half as fast as in the beginning. Hence the pots are 

 then giving off only half the heat that was being generated at 

 first. The residue that accumulates in an oil-pot from the 

 burning oil also reduces its efficiency. 



In equipping an orchard for heating with oil, in addition 

 to at least 100 heaters to the acre, or their equivalent in case 



» Bull. 6, Of. of the Pathologist and Local U. S. Weather Bur. 

 Sta. for Rogue River Valley, Ore. 



