44 BULLETIN NO. 161 



cloths. This was done when the temperature of the surrounding 

 area was cooling and it was found that the treated area cooled 

 at the same rate as the untreated area. 



7. Electric heaters were placed in the bottom of an approxi- 

 mately air-tight box, two and one-half feet by four and one-half 

 feet and seven and one-third feet deep, and they gave a rise in 

 temperature of 14. lo F. With 22 pounds of carbon dioxide 

 (three times the volume of the box) which had been warmed to 

 the same temperature as the box before it entered, the heaters 

 gave a rise of 2.8o F. more than with no smudge, the gas being 

 liberated in 15 minutes. A test of the air inside of the box show- 

 ed three per cent carbon dioxide there. This result was dupli- 

 cated on a larger scale by heating (with electric heaters) an 

 area 500 square feet surrounded by walls. 



8. During April the upper two or three inches of the ground 

 is only slightly warmer than the air. This condition lasts only 

 a few hours during the night, so that the rate of transfer of 

 heat upward is slow and spring frosts usually occur several 

 nights in succession with the intervening days comparatively 

 cool; hence, smudging would be quite ineffective on the second 

 and third night, and we think smudging is entirely unsatisfactory 

 unless heat be supplied with it. 



9. Tests to see the effect of spraying warm water over the 

 tree which would liberate heat on cooling and on freezing and 

 should help retain heat of: the earth by acting as a smudge did 

 not prove that the practice was satisfactory. The sediment in 

 the water, clogged the really fine spray and the coarse spray 

 even though the water was warm before leaving it, collected in 

 the fruit buds and froze them, producing the same effect as a 

 storm of sleet. 



10. One hundred horse-power of electrical energy when con- 

 verted into heat in the open air gave a temperature rise of 20o 

 F., the temperature outside being 70o F. It required approxi- 

 mately 14 watts per square foot to obtain lo F. rise in tem- 

 perature. 



11. On clear, quiet, frosty nights the out-doors can be heat- 

 ed with pots because the heated air only rises 50 to 75 feet, due 

 to the temperature inversion layer. 



12. A table containing results of 15 investigations of other 

 stations shows that with 100 heaters to an acre the orchard will 

 remain about 4o F. warmer than the surrounding unheated 

 area. Winds of ten miles an hour reduce this to less than one 



