River Temperature. 
307 
The Means of Observations made on the Brahmaputra and its 
small tributary the Kundeel, at Sadiyd, in September 
1836, by Dr W. Griffith (“Journal of the Bengal 
Fahrenheit Scale. 
Asiatic Society,” vol. v., p. 827). 
ee Air over the | Ai the | Water ofthe | Water of tl 
Hour. | Air in House. Rude. , Bema utte. eaiiidaciatra: Bondeel:.- 
6 A.M. 75°°6 10:3 72°°0 66° 2 75°°5 
2 P.M. 83°°9 Sioa 82°'9 67°°6 78°'6 
6 P.M. 82°°9 S122. 73°°8 67°°7 78°°4 
Mean? 79°°9 79°°8 74°°8 67°°0 dig 
From this table it appears that the cooling influence of 
the Brahmaputra on the air over it was but slight during 
the heat of the day, being at 2 p.m. only 1°. By 6 p.m. the 
air had lost 9° through the chill of the river, and it is 
apparent that the cooling was principally accomplished in 
the sunset. hours. The thermal regime of the Brahmaputra 
is of course very exceptional. Most rivers in different 
latitudes are warmer than the air at night, and the time at 
which the chill of the river ought to be most effective would 
be about sunset, when the air and water temperatures would 
be usually not far apart; whilst in the heat of the day, when 
the water is much the coolest, its chilling influence, accord- 
ing to the Brahmaputra observations, would be slight. These 
remarks certainly apply to the Senegal observations in August, 
and probably also to those of Dr Marcet on the Nile in 
March, and no doubt they are true also of most rivers that 
have a plane of temperature not far removed from that of 
the air, as in the case of our own rivers. But there are 
instances where the chilling effect would be pronounced, 
namely, as regards large rivers that, like the Upper Yangtse, 
have a relatively low plane of summer temperature in com- 
parison with the air (Blakiston). 
The following rules may be formulated from the Brahma- 
1 Estimated from the 6 A.M., 6 P.M, and the (computed) noon and mid- 
night temperatures. 
