1881.] 



and rainfall to temperature in India. 



77 



while the influences of cloud and of the wind on which the cloudiness 

 depends, are such as tend to raise the temperature, the evaporation of rain, 

 as already pointed out, tends to lower it. That the preponderating agency 

 is that of nocturnal radiation, receives confirmation from the figures in the 

 following table, which is based on the register of the same six stations in 

 the Punjab. This shows, together with the temperature anomaly of the 

 months in question, the anomaly of the nocturnal depression of the thermo- 

 meter for terrestrial radiation, and also that of the solar thermometric 

 excess. The signs plus and minus indicate the magnitude of the effect in 

 each case, i. e., the variations of these temperature differences, as compared 

 with the corresponding respective averages. A -f sign indicates a greater 

 nocturnal depression (below the air temperature) than the average, or a 

 greater excess of the solar thermometer (above the air temperature) and 

 viee versd. The comparison is restricted to the last three years, for which 

 alone we have comparable observations of the nocturnal radiation. 





1877. 



1878. 



1879. 



Months. 



Ja 



CD 



Nocturnal de- 

 pression ano- 

 maly. 



m 



CD 



o 



O & 



m 



—25 



—3-6 



f§ 



CD 



u 2 

 •1-1 -+-> 



< 



Nocturnal de- 

 pression ano- 

 maly. 



m 



CD 



o 



<D ?*~> 



ea 



ai 



o c^ 



CD 

 U 



Nocturnal de- 

 pression ano- 

 maly. 



CO 

 GO 



CD 



CD >> 



si 



rS CI 



O cS 

 GG 



November, 



December, .... .... 



+ 4-0 

 + 0-7 



—1-6 



—1-7 



—0-6 

 —0-5 



+ 1-0 

 + 1-0 



-07 

 + 1-4 



—2 5 

 —1-0 



+ 07 

 + 0-8 



+ 1-7 

 + 0-2 



In every case, the air temperature anomaly has the opposite sio-n to 

 that of the nocturnal depression, indicating that, when the loss of heat by 

 nocturnal radiation is less than usual, the mean air temperature of the 

 month (not of the night only) is above the average ; and that when the 

 nocturnal radiation is greater than usual, the mean air temperature is below 

 the average ; and this action is sufficient to outweigh the varying intensity 

 of solar radiation. 



It is only in the months of November and December, that the air 

 temperature shows, distinctly, the predominant influence of nocturnal 

 radiation, as affected by cloud. In October, solar radiation on the one 

 hand, and evaporation on the other, seem to be more effectual in influ- 

 encing the air temperature than the variations of nocturnal radiation ; 

 and thus, an excess of cloud is more frequently accompanied with a nega- 

 11 



