AGRICULTURAL EXPERIMENT STATION. 165 



the comparison given below, the minimum thermometer was four 

 feet above the ground and the terrestrial radiation thermometer 

 was within six inches of its surface. The results are based on 

 monthly averages from M:iy to October inclusive, 1889, from 

 April to October inclusive, 1890, and from April to October 

 inclusive, 1891. 



Table Showing Loss of Heat by Terrestrial Radiation. 



1889. 



May. June. July. Aug. Sept. Oct. Mean, 

 o o o o o o o 



Mean of minimum temperatures. 40.63 53.25 55. 08 53.65 49 07 33.01 48.50 



Mean of Temp, from Ter. Rad. Ther 38.48 49.20 50 50 47.06 44.00. 28.48 43.17 



Loss of heat by radiation 8.15 4.05 4.49 5.39 4.74 5.43 5.33 



1890. 



April. May. June. July. Aug. Sept. Oct. Mean 



ooo oo ooo 



Mean of minimum temperatures 29.17 42.52 48.71 53.01 53.52 45.32 36 05 44 13 



Mean of Temp, from Ter. Rad. Ther... 19.95 37.10 42.10 44.55 40.25 3S.40 27.14 36.50 



Loss of heat by radiation S.22 5.42 6.61 9.06 7.27 6.92 9.91 7.63 



1891. 



April. May. June. July. Aug. Sept. Oct. Mean 



ooooo o oo 



Mean of minimum temperatures. ...30.22 37.67 49.18 53.15 54.07 49.23 34.95 44.07 



Mean of Temp- from Ter. Kail. Ther.. 24.45 29.09 40.S7 43.94 47.40 42.22 25.60 36.23 



Loss of heat by radiation 5.77 8.58 S.31 9.2i 6.67 7.01 9.35 7.84 



On cloudy nights the difference in the reading of the two ther- 

 mometers is small, and on exceptionally clear (dry) nights it is a 

 maximum. The greatest range observed was 19°. 5. On the 

 morning of July 2, 1889, the radiation thermometer was the 

 higher, showing that the moist air resting upon the surface of the 

 ground served as a warm blanket, and that the amount of heat 

 absorbed was greater than that radiated. From the table above 

 it appears that the mean radiation for the three seasons was G°.93. 



Solar Radiation. 

 The temperature of the atmosphere does not indicate the inten- 

 sity of the sun's heat, as only a small percentage is absorbed as 

 the rays are transmitted through the air. The maximum ther- 

 mometer in the shade, therefore, does not give the intensity of 

 solar radiation ; neither does exposure of an ordinary thermometer 

 to the direct rays of the sun, in consequence of the cooling effects 



