ME. H. F. BLA.NFOED ON THE WINDS OF NOETHEEN INDIA. 
595 
complete than could be desired. With the exception of the Lower Provinces and 
Bombay (Colaba Observatory) and two stations in the North-western Provinces, the 
available humidity-registers give observations of the day hours only ; and in order to 
obtain comparable values, I have multiplied these by factors obtained empirically from 
the registers of Benares and Roorkee (see note to Table V.). I have rejected the data 
of several stations which it would have been desirable to add, since they give results so 
much above other stations similarly situated, as to leave me in little doubt of their 
untrustworthiness. The Table of vapour elasticities is computed directly from those of 
the mean humidity and the mean temperature, except in the cases of Calcutta and 
Bombay, where the figures have been obtained from the psychrometer observations 
taken hourly and reduced for each observation. With these two exceptions the values 
are therefore in all cases somewhat too low. 
Since, as is well known, Northern India with Eastern Bengal presents in different 
parts the extreme modifications of continental and maritime climate, it might be expected 
that the range of vapour-tensions shown by a comparison of the registers would be very 
great ; and such is, indeed, the case. The extreme amounts shown in the present Table 
are furnished by Mooltan and False Point — the annual mean of the former being 0382 
inch, while that of the latter is 0862 inch*. 
But this, the geographical range, is in certain cases surpassed by the annual range at 
one and the same station. Of this the stations in the Gangetic plain offer the most 
striking examples. Thus at Patna the mean vapour-tension rises from 0-328 in January 
to 0969 in July, at Benares from 0325 in December to 0*977 in July, and at Roorkee 
from 0293 in December to 0-911 in July, the ranges being therefore 0-641, 0*652, and 
0-618 respectively. On the other hand, Bombay and Akyab, the climates of which are 
more equable than that of any other station, show a range of 0-335 and 0-374 only. 
The lowest vapour-tension occurs in January at most of the stations, coinciding with 
the minimum of . temperature. At one or two only it appears to be slightly lower in 
December. Such is the case at Cuttack, False Point, and Saugor Island, where sea- 
winds set in very early in the year (see ante , Part I. pp. 576, 578), and at Benares. 
Generally in the upper part of the Gangetic plain, in Central India, and the Punjab 
the means of December and January are almost equal. In the Gangetic delta and 
Orissa, on the coast of Arakan, and in Eastern Bengal and Lower Assam f the 
elasticity rises regularly and rapidly up to the setting in of the rains, indicating a steady 
increase in the supply of vapour as well as a rising temperature. But in the dry regions 
of the interior, where land-winds prevail throughout the spring months, the rise of 
vapour-tension is very slow, not much greater probably than would be produced by the 
actual rise of temperature on the local supply of vapour. The elevation, when the 
summer monsoon begins to be felt in June or July, is then very sudden, and the fall at 
the close of the monsoon between September and November equally strongly marked. 
* The January mean at the former station is 0-208 inch; the May mean at the latter 1-079 inch. 
t Probably also in Upper Assam; hut I have no register for that regioD. 
4 L 
MDCCCLXXIV. 
