34 THE APPLE 



referred to what are known as psychrometric tables, from which 

 the temperature at which dew or frost will form may be found. 



Psychrometric readings should be made late in the evening, and 

 the dew point will be approximately the lowest temperature of the 

 following night. Practice in making these readings and records 

 of the predicted dew point and lowest temperatures occurring for 

 several nights previous to the frosty time will familiarize the 

 observer with the use of the instrument. 



Heating the small home orchard. The practicability of heating 

 small orchards is often questioned. It is comparatively much easier 

 to heat a large area than a small one. But there are many home 

 orchards, both on farms and on city lots, where oftentimes the fruit 

 is more highly prized than it would be in a commercial orchard. 



After the first year's cost of installation, the cost of protecting 

 the home orchard will amount to between one and two dollars per 

 acre per hour. No estimate of the cost of labor or of oil storage is 

 given, as the owners of small tracts can easily handle the equip- 

 ment without extra labor. The oil will come in barrels and can be 

 distributed from these, so that no storage is necessary. 



Where the fruit is highly prized, this expense will not be pro- 

 hibitive, and under ordinary conditions the fruit can be saved 

 on small areas. Windbreaks will be found especially valuable in 

 protecting small areas during high winds. 



The need of thermometers. Accurate thermometers should be 

 provided. At least one high-grade tested thermometer should be 

 available in order to test less expensive ones. Faulty instruments 

 are sure to cause loss, as firing may be begun too late and injury 

 to buds result, or if the heaters are lighted before the danger 

 point is reached, fuel is lost which may be needed at a critical 

 time before sunrise. 



An electric-alarm thermometer can be secured for about twenty 

 dollars which will ring an alarm when the danger point at which it 

 is set is reached. This will save considerable loss of sleep, which 

 is valuable if several frosty nights arc experienced and when the 

 spraying season demands attention. 



It will be well to place the thermometer by which the fires are 

 to be lighted in the lowest part of the orchard. Cool air settles in 

 low places, and these are often much cooler than the higher points. 



