243 
continual arrival of fresh warm air, until the moment when 
rain began to fall ; the rise would then receive a check, and 
if the rain continued, a decided fall of temperature would 
take place. If, therefore, we take a day of rain, the day 
before, and the day after, the difference of the mean tem- 
peratures of the day of rain and the day before, ought to be 
less than that of the mean temperatures of the day of rain 
and the day after. It will be seen that this conclusion is 
borne out by the following results of the Greenwich and 
Oxford observations : — 
Mean temp. 
of day 
before Rain. 
Mean temp, 
of day 
of Rain. 
Mean temp. 
of day 
after Rain. 
Greenwich Observations.. 
Oxford ,, 
49-25 
49-50 
4°9-27 
49-63 
48- 98 
49- 44 
Should the supposition that a considerable portion of the 
aqueous vapour in the atmosphere may lose its latent heat 
without becoming visible as cloud or fog be held to be 
inadmissible, it appears to me that we shall then have no 
alternative but to conclude that the generally received theory 
of latent heat is inapplicable to meteorological phenomena, — 
a conclusion at least as questionable as the view which I 
have ventured to advance. 
