408 CLIMATE OF SIKKIM. Appendix F. 



This distribution of the seasons has a most important effect upon 

 vegetation, to which sufficient attention has not been paid by culti- 

 vators of alpine Indian plants ; in the first place, though English 

 winters are cold enough for such, the summers are too hot and dry ; 

 and, in the second place, the great accession of temperature, causing 

 the buds to burst in spring, occurs in the Himalaya in March, when 

 the temperature at 7000 feet rises 8° above that of February, raising 

 the radiating thermometer always above the freezing point, whence 

 the young leaves are never injured by night frost : in England the 

 corresponding rise is only 3°, and there is no such accession of 

 temperature till May, which is 8° warmer than April ; hence, the 

 young foliage of many Himalayan plants is cut off by night frosts in 

 English gardens early in the season, of which Abies Webbiana is a 

 conspicuous example. 



The greatest heat of the day occurs at Dorjiling about noon, owing 

 to the j>revalent cloud, especially during the rainy months, when the 

 sun shines only in the mornings, if at all, and the clouds accumulate 

 as the day advances. According to hourly observations of my own, 

 it occured in July at noon, in August at 1 p.m., and in September 

 (the most rainy month) there was only four-tenths of a degree differ- 

 ence between the means of noon, 1 p.m., and 2 p.m., but I must 

 refer to the abstracts at the end of this chapter for evidence of this, 

 and of the wonderful uniformity of temperature during the rainy 

 months. In the drier season again, after September, the greatest heat 

 occurs between 2 and 3 p.m. ; in Calcutta the hottest hour is about 

 2*45 p.m., throughout the year ; and in England also about 3 p.m. 



The hour whose temperature coincides with the mean of the day 

 necessarily varies with the distribution of cloud and sunshine ; it 

 is usually about 7 a.m. and 7 p.m. ; whereas in Calcutta the same 

 coincidence occurs at a little before 10 a.m., and in England at 

 about 8 a.m. 



Next to the temperature of the air, observations on that of the 

 earth are perhaps of the greatest value ; both from their application 

 to horticulture, and from the approximation they afford to the mean 

 temperature of the week or month in which they are taken. These 

 form the subject of a separate chapter. 



Nocturnal and solar radiation, the one causing the formation of 



