AGRICULTURAL EXPERIMENT STATION. 161 



1890. 



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



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Mean of niininiuni temperatures 29.17 42.ij2 48.71 .53.61 .53..52 4.5..32 36.0.5 44.13 



Mean of Temp, from Ter. Rad.Ther.. 19.95 37.10 42.10 44..55 46.25 38.40 27.14 36..50 



Lose of heat by radiation 8.22 5.42 6.61 9.06 7.27 6.92 9.91 7.63 



1891. 



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

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Mean of minimum temperatures 30.22 37.H7 49.18 53.15 54.07 49 23 34.95 44.07 



Mean of Temp, from Ter. Rad.Ther.. 24.45 29.09 40.87 43.94 47.40 42 22 25.60 36.23 



Loss of heat by radiation 5.77 8.58 8.31 9.21 6.67 7.01 9..35 7.84 



1892. 



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

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Mean of minimum temperatures 30.32 39.08 50.73 54.65 .55.77 45.69 34.47 44.39 



Mean of Temp, from Ter. Rad. Ther.. 22.29 30.64 41.89 45.05 46.38 37.45 28.02 35.96 



Loss of heat by radiation 8.03 8.44 8.84 9.60 9.39 8.24 6.45 8.43 



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° Occasionally, 

 the reading of the radiation thermometer is higher than that of 

 the minimum thermometer, showing that the moist air at such 

 times, resting upon the surface of the ground, serves as a warm 

 blanket, and that the amount of heat then absorbed is greater 

 than that radiated. The table above shows that the mean radia- 

 tion for the four seasons was 7.31°. 



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 

 of draughts of air. In order to avoid the effects of currents of 

 air, the vacuum solar radiation thermometer has been devised. 

 "This consists of a blackened bulb radiation thermometer inclosed 

 in a glass tube and globe, from which all air is exhausted. Thus 

 protected from the loss of heat which would ensue if the bulb 

 were exposed, its indications are from 20° to 30° higher than when 

 placed side by side with a similar instrument with the bulb exposed 

 to the passing air." By the use of this icstrument the amounts 

 of solar radiation at different places and in different seasons at 



