ON THE THEORY OP RAIN. 



403 



Greenwich Observations. 



Year 



Number 



of 



Rainy Days 



Mean Temp. 



of 

 Rainy Days 



Mean Temp. 



of 



the Year 



1852 

 1853 

 1854 



152 



184 



51*39 



47-62 

 48-80 



50-66 . 



47*49 

 48-80 



General Means. 



160-3 



49-27 



48-98 



Oxford Observations. 



Year 



Number 



of 



Rainy Days 



Mean Temp. 



of 

 Rainy Days 



Mean Temp. 



of 



the Year 



1855 

 1856 



1857 



140 



154 

 146 



49-84 

 49-09 

 49-96 



47-10 

 48-70 

 50-40 



Greneral Means. 



146-6 



49*63 



48-73 



It appears, therefore, that the excess of mean tempera- 

 ture of rainy days, over the mean temperature of the year, 

 on an average of three years, is only o°*29 by the Green- 

 wich observations, and o°'go by the Oxford observations ; 

 but as the winds which bring rain come principally from 

 warmer latitudes, the mean temperature of rainy days 

 ought, on that account alone, to be greater than the mean 

 temperature of the year. Dividing the winds into two 

 groups, northerly and southerly, it appears from the 

 Oxford observations that out of 218*5 days of fair weather 

 in the year, the wind was from the northern half of the 

 compass on 131 "5 days, and from the southern on the 

 remaining 87; but out of 146*5 rainy days the wind was 

 from the northern half on only 64*5 days, and from the 

 southern on 82. Moreover, the quantity of rain which 

 fell with winds from the southward was nearly four-tenths 

 greater than that which fell with winds from the north- 

 ward. Calculating the mean temperature of rainy days 

 from the mean temperatures of the winds which prevail 

 on those days, the result is 5o'''05 ; but we have seen that 



