390 Scientific Intelligence — Meteorology. 



change the temperature they had on tlieir production, which depends 

 on the height of the clouds whence they come, and the heating of 

 these on their upper surface hy the sun's rays. After the rain- 

 drops, on their first formation, by reason of the latent caloric of the 

 vapour becoming sensible, have acquired a higher temperature than 

 the surrounding medium, they still rise somewhat in temperature ; 

 whilst, as they fall through lower, warmer, and moister strata of air, 

 vapour continues to be precipitated upon them, and they increase in 

 size (Bischof, Warmelehre, S. 73) ; but this rise is compensated 

 by evaporation. Cooling of the air by rain is effected (setting aside 

 what probably belongs to the electrical processes attending thunder- 

 storms) by the drops, which are themselves of lower temperature, in 

 consequence of the place of their formation, and, farther, bring down 

 a portion of the higher colder air ; and then by moistening the 

 ground, and giving occasion to evaporation. Such are the usual re- 

 lations of the phenomenon. When, in rare cases, the rain-drops are 

 warmer than the lower strata of the atmosphere (Humboldt, Relat. 

 Hist., t. iii., p. 513), the i-eason may perhaps be sought for in su- 

 perior warmer currents, or in a higher temperature acquired by ex- 

 tended and not very dense clouds, exposed to the action of the sun s 

 rays. How, for the I'est, the phenomena of supplementary rainbows 

 (explained by the interferences of light) are connected with the size 

 of the falling drops and their increase ; and how an optical pheno- 

 menon, when rightly observed, may enlighten us in regard to a me- 

 teorological process, according to diversity of zone, has been shewn, 

 with great acuteness, by Arago, in the Annuaire for 1836, p. 300. 

 — Cosmos, No. 4, p. 443. 



2. On the Height of the Snow-Line in India. — Whilst the most 

 learned and experienced travellers in India, — Colebrooke, Webb, 

 Hodgson, Victor Jacquemont, Forbes Koyle, C Von Hiigel, and 

 Vigne, who are all familiar with the Himalaya, from personal exa- 

 mination, are agreed as to the higher elevation of the snow-limit on 

 the Thibetic declivities of the range, the fact is called in question by 

 Gerard, M'Clelland (the editor of the Calcutta Journal), and Lieut. 

 Thomas Hutton (assistant surveyor of the Agra division). The ap- 

 pearance of my work on Central Asia excited the controversy on the 

 subject anew. A number of M'Clelland and Griffith's Calcutta 

 Journal of Natural History, vol. iv., 1844, January, however, con- 

 tains a very remarkable and decisive notice of the snow-limit of the 

 Himalaya. Mr Batten (Bengal service), writes from the camp of Seni- 

 ulka, on the Cosillah river, in the province of Kumaon, as follows : — 

 " I have only, but with surprise, heard of the statements of Mr Thomas 

 Hutton, respecting the limits of perpetual snow. I feel the more 

 called upon to contradict such statements, as Mr M'Clelland goes 

 so far as to speak (Hutton, Journal of the Asiatic Society of Bengal, 

 vol. ix., Calcutta, 1840, p. 575, 678, and 580), of the honour which 

 Mr Hutton has done himself in detecting a wide-spread error. It is 



