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winds w'hich 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 
northward. Calculating the mean temperature of rainy days 
from the mean temperatures of the winds which prevail on 
those days, the result is 50°*05 ; but we have seen that the 
observed mean temperature is only 49°*63, or 0°*45 less than 
the computed. It appears, therefore, that a wind accompanied 
with rain is, in general, sensibly cooler than the same wind 
attended with fair weather, and that whatever may be the 
mode of formation of rain it may be regarded as a cooling 
process ; and this view is borne out by the fact that the mean 
temperature of the days next after days of rain is sensibly less 
than that of the days of rain. According to the Greenwich 
observations the diminution is 0°*29, and according to the 
Oxford observations it is 0°*19. But if the vapour brought 
by a rainy wind retains its latent heat up to the moment 
that actual precipitation of rain takes place, the sudden disen- 
gagement of this heat, although occurring in the higher 
regions of the atmosphere, ought to have a very sensible 
effect in raising the mean temperature of rainy days ; but as 
no such effect is produced we may conclude that the greater 
portion, if not the whole, of the moisture from which the rain 
is formed, had previously lost all its latent and also a small 
portion of its sensible heat. 
