4 BULLETIE" 821, U. S. DEPARTMEIiI"T OF AGRICULTURE. 



to provide a more complete combustion of fuel with a consequent 

 small amomit of smoke or smudge, were tried during this period, 

 but they were abandoned later, owing to mechanical difficulties and 

 other causes. 



Usually one heater for every tree was provided, and in some cases 

 two rows of heaters were arranged on the north and west sides of the 

 orchards. The heaters were usually placed in the center of the 

 square made by four trees, as shown in figure 3, so as to avoid as far 

 as possible injuries to the fohage and fruits from the flames or from 



Fig. 2. — The type of heaterin most common use in the Corona district. From left toright in the fore- 

 ground are shown a gasoline torch for lighting the orchard heaters, a can for distributing oil to the 

 heaters, and a style of heater of about 9 gallons' capacity. In the background stands a small oil 

 tank. The oil is drawn off from the tank through a valve at its base, shown at the right. 



close contact with the heaters. They were Ughted, as a rule, when 

 the temperature in the orchards dropped to 31° F., although the 

 temperatures at which lighting began depended somewhat upon other 

 conditions than those of temperature and the time of night at which 

 the low temperature was reached. For example, if the temperature 

 dropped to 32° F. before midnight the heaters were usually lighted 

 at this temperature. If the temperature did not drop below freezing 

 until the early morning, as was frequently the case, the heaters were 

 usually lighted at 30° F. In some cases \fhen the temperature did 

 not drop too near the danger point until 5 to 6 a. m. the heaters were 

 not hghted until the thermometer reached 29° or 28° F. 



