Frost and the Prevention of Damage by It. 45 



but fairly satisfactory method of sheltering a thermometer which is 

 used only at night is to place a large thin flat board horizontally 

 directly above it. The thermometer should be placed close up under 

 the board so as to cut off as much of the sky as possible. 



In reading a thermometer on a cold night, care should be taken not 

 to breathe directly on it. Whenever possible, an electric flash-light 



FIG. 19. Types of thermometers used by the Weather Bureau to register the highest and 



lowest temperature. 



should be used in making readings. When matches or candles are 

 used to illuminate the thermometer, the temperature may be raised 

 a degree or more before the reading can be made, which may in some 

 cases results in loss of fruit through not lighting the heaters in time. 

 Every orchardist who has frost-fighting equipment should have at 

 least one accurate dependable thermometer to be placed in the coldest 

 part of the orchard, preferably one which will register the minimum 

 temperature. (See fig. 19.) Cheaper thermometers can be scat- 

 tered throughout the remainder of the orchard. These should be 

 carefully compared with the standard thermometer at least once each 

 year and inaccuracies noted. Those which are found to be in error 

 more than one degree near the freezing point should be discarded. 

 Cards showing the corrections to be applied at different points on the 



