elevated Rain-gauge, as caused by Wind. 431 



that by experiment he has proved rain to be sufficiently cold to 

 produce precipitation even when the air is far from being 

 saturated. 



In the Greenwich Meteorological Observations for 1843 (p. 123) 

 it is stated that, in occasional observations on the temperature of 

 the rain, " It has been always found that when the rain has been 

 warm with respect to the temperature of the air at the time, no 

 differences have existed in the quantities of rain collected at the 

 different heights ; but that when the temperature of the air has 

 been higher than the temperature of the rain, a difference has 

 always existed." It is quite surprising that these writers do not 

 perceive that their experiments tell directly against their own 

 conclusions, or at least tell nothing at all to the purpose. If it 

 is the rain in the lower gauge, as is most likely, which was found 

 to be cold, it simply proves that condensation of vapour has not 

 taken place, otherwise the rain would have been warmed thereby. 

 If, however, the rain in the higher gauge be found of a low tem- 

 perature, it tells us nothing at all to the purpose, unless we like- 

 wise prove that the same rain, on reaching the lowest gauge, is 

 of a much higher temperature. In short, we must have a change 

 of temperature observed ; and such an observation has never 

 been recorded, so far as I am aware. 



24. As a further objection to the condensation theory, it may 

 be added that Arago, in stating it*, argues that the difference of 

 the rain collected in the two gauges should be greater as the air 

 is more moist, a consequence which he confesses is not at all 

 conformable to experience. This remark is strikingly borne out 

 by the fact already stated, that the apparent increase of rain 

 between the higher and lower gauges is usually greatest during 

 the month of March. Now this is the month of prevalent dry, 

 cold, north-east winds and gales, the very circumstances under 

 which the condensation theory is most utterly inadequate or in- 

 applicable. 



25. A single secondary argument in favour of the supposed 

 increase of rain-drops remains to be disposed of. Arago has 

 remarked f that the internal supernumerary fringes of a rainbow 

 are never seen on the lower parts of the bow near the surface of 

 the earth. Now the supernumerary bows were explained by 

 Dr. Young on the theory of interference of undulations ; and 

 their appearance indicates that the drops of rain upon which the 

 bows appear are of exactly uniform size. Not observing the 



* Annuaire du Bureau des Longitudes, pour Fan 1824, p. 161. 



f " II faut done que pendant leur descente verticale, les gouttes d'eau 

 aient perdu les proprietes dont elles jouissaient d'abord; il taut qu'elles 

 soient sorties des conditions d'interference eJjUcaces ; it faut qu'elles aient 

 beaucoup grossi." 



