442 



The Physical Condition of 



[Oct. 



the radiation of heat from extensive wastes of sand is prevented by the 

 freshes which cover them, and the volume of water increased, as well 

 as the rapidity of the rivers by the melting of the snow ; the rivers then 

 present a temperature much beneath that of the atmosphere whose 

 heat they now contribute to lessen, just as they promoted an opposite 

 effect during the cold season. Nor is this influence of large bodies of 

 water upon climate confined to Assam ; it applies equally to all great 

 valleys similarly situated, and especially to those inland provinces of 

 China whose productions are so similar. 



From what I could learn regarding the temperature of the hot sea- 

 son, it would appear that82o Fahr. at Suddya, is considered as exces- 

 sive as 96° in Calcutta ; and although the quantity of rain that falls 

 during the year may be supposed from a combination of circumstances, 

 to be much in excess of what falls in Bengal, yet there is reason to sup- 

 pose that during the months of July, August, and September, the quan- 

 tity in Assam may be no greater than elsewhere ; the absence of any 

 season of perfect drought being the peculiar feature of the climate. If 

 however the theory by which I have endeavoured to account for the pe- 

 culiarity of wind, during the S. W. monsoon be correct, it is difficult to 

 conceive that clouds and showers should not be frequent, or at least 

 occasional during the months of April and May.* 



From these general observations on the climate of Assam, we may 

 venture to infer that in regard to heat and moisture, it possesses many 

 peculiarities when compared with the open plains of Bengal. 



Looking down from the Kossia mountains into the valley, in 

 November, it presented the appearance of one vast lake, from the 

 sheet of vapour under which it was concealed for several hours daily, f 

 "While ascending the Bramaputra in December, the weather was 

 generally dark and gloomy with some rain. During the time we were 

 in the forests, which embraced the greater portion of January, we 



* On two winds of different temperatures and differently saturated coming into con- 

 tact, the result would be the formation of a cloud or the precipitation of rain according 

 to the proportion of moisture contained in the warmer vapour. See Prout's Bridge- 

 water Treatise, 



■t This was sometimes observed even for several days, and may be considered to have 

 been actually the case during the greater part of the two following months, but being 

 then in the valley we could not perceive it otherwise than by the shade. The effects of 

 these clouds upon vegetation, and in checking extremes of temperature, may be con- 

 ceived from the circumstance that when they were first observed from the Kossia 

 mountains, a keen N. E. wind blew daily, and from which the valley was quite pro- 

 tected by the vapour. 



