594 
ME. H. F. BLANFOED ON THE WINDS OF NOETHEEN INDIA. 
On the average of the whole year, Hazareebagh is then 4 0, 3 cooler than Berhampore, 
which, for a difference of 1949 feet, gives a mean of 1° Fahr. for 453 feet. The tem- 
perature-difference is least in May, when it amounts to only 0°*4 ; but Hazareebagh is 
still the cooler, and this station is therefore above the range at w 7 hich elevation produces 
an actual increase of summer temperature. The difference is greatest in October ; but 
from July to December it remains above the average of the year, and thus (in respect of 
the rainy season) contrasts strongly with the corresponding variation at hill-stations. 
The variation may, I think, be traced partly to the character of the winds, but chiefly 
to the local absorption and radiation of the solar heat. In May there is at Berhampore, 
as at all stations on the delta, a very large excess of south and east, that is to say sea- 
winds, more or less deflected ; while at Hazareebagh there is still an excess of west and 
a large proportion of north-west, that is hot land-winds. In October the preponderance 
of sea- and land-winds respectively at the two stations is similar, but the land-winds are 
at this season of the year the cooler of the two. But a further and more important 
cause tending to produce the observed variation is the difference of nocturnal radiation 
and diurnal absorption of solar heat in those months. This difference is at its minimum 
in May and its maximum in October in the former ease, and vice versd in the latter. 
The mean of three years’ observations of a Rutherford’s minimum thermometer (placed 
above the ends of the grass on forked sticks, and radiating its heat freely during the 
night time) is as follows : — 
Hazareebagh. Berhampore. Diff. B.— H. 
May ... . 72°-2 73°-5 l°-3 
October . . . 59°-8 71°-8 12°-0 
On the other hand, the mean of three years’ observations of a maximum blackened bulb- 
thermometer enclosed in a vacuum-tube and freely exposed to the sun, the observations 
having been recorded on all days, whether clear or overcast, is as follows : — 
Hazareebagh. Berhampore. Diff. H.— B. 
May ... . 160°-5 150°-8 9°-7 
October . . . 140°-3 142°*7 — 2°-4 
A similar excess of nocturnal radiation and decrease of insolation, but less in amount, 
characterizes the rainy months at Hazareebagh, and serves to explain the lower tempe- 
rature of that station. I need not pursue this subject further at present. The important 
point which is so strongly indicated by the above figures is that the temperature of the 
atmosphere over the plateau is largely affected by the absorption and radiation of the 
ground, and therefore does not represent that of the free atmosphere at an equal height 
over the plains. Any difference of temperature thus arising between two masses of air 
in the same horizontal plane must tend to produce convection-currents ; and of such 
currents tending to or from the plateaux of Central and Upper India and Western 
Bengal we have many instances. 
Vapour-tension, Humidity, and Rainfall. — The existing records of the hygrometric 
state of the atmosphere, from which I have constructed Tables IV. and V., are less 
