404 MR. JOSEPH BAXENDELL 



the observed mean temperature is only 49°'63, or o°'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 what- 

 ever 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 dimi- 

 nution is o°'29, and according to the Oxford observations 

 it is o°-i9. But if the vapour brought by a rainy wind 

 retains its latent heat up to the moment that actual preci- 

 pitation of rain takes place, the sudden disengagement 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. 



The questions now arise — ist, What becomes of the 

 enormous quantity of heat given off by the vapour which 

 is condensed in the atmosphere? and 2nd, As the mois- 

 ture which forms rain is not in the state of a true vapour, 

 is it in the ordinary liquid state, or in some other state 

 not hitherto recognised by meteorologists and chemists ? 

 With regard to the first question, it may be remarked that 

 air nearly saturated with vapour, has probably a greater 

 power of radiating lieat than dry air. The upper portion 

 of a wind charged with vapour would therefore undergo a 

 rapid cooling, and as the vapour which loses its latent heat 

 does not immediately affect the transparency of the air, 

 this process would go on unchecked for ?ome time, and 

 would gradually extend to the lower strata; the vapour 

 which had lost its latent heat would also gradually 



