ORCHARD HEATING 5 



Henry J. Cox (b) of the U. S. Weather Bureau working in the 

 cranberry districts of Wisconsin. . Sections of these bogs were 

 drained, sanded, cultivated, and either left bare or thinly vined. 

 This resulted in a lowering of the heat capacity of the ground. 

 The highest maximum soil temperatures for the day, the lowest 

 minimum soil temperatures for the night, and the highest 

 minimum air temperatures occurred in these sections, while in 

 the uncultivated marsh, which was poorly drained and had a 

 thick growth of vegetation on it, just the reverse was found to 

 be true; the minimum temperature of the air in the sanded 

 section being seven degrees higher than in the untreated bogs- 

 The unfortunate thing about this method when applied to 

 orchards is the fact that these differences in temperature of the 

 air above the districts mentioned disappears at a height of three 

 feet above the ground ; that is, the method is ineffective in modi- 

 fying the minimum temperature of the air at heights above 

 three feet. 



FROST AND CLEAR NIGHTS 



The earth receives heat from the sun during the day, and 

 during the night this heat is continuously lost by radiation to 

 outer space, for which reason the temperature usually falls all 

 night long, the rising of the sun starting the cycle again. It 

 has been observed that on clear nights, the minimum tempera- 

 ture is low (frosts usually occur on clear, quiet nights) while 

 on cloudy nights the air does not become so cold. The explana- 

 tion lies in the fact that the clouds act as a mantle which holds 

 the heat in and prevents it from being dissipated into space. It 

 has been proposed . that, on the occasion of a clear night when 

 the weather threatens a frost, the orchard be covered with an 

 artificial cloud or mantle. This mantle is for the purpose of 

 keeping the heat in the orchard that was stored in the ground on 

 the previous day when the sun was shining- It is also supposed 

 to keep the temperature from rising too fast the next morning 

 when the sun comes up, the feeling being that if the buds have 

 been frozen the damage would be less when the rate of thaw 

 is- slow. 



SMUDGE 



With these points in mind, various methods of smudging 

 have been practiced; a common one being that of drawing 

 through the orchard a wagon covered with wet burning straw, 

 so that the smoke and the evaporated water would hold the heat 



(b). Descriptive Meteorology, Moore pp. 108-109. 



