610 
MR. H. F. BLANFORD ON THE WINDS OF NORTHERN INDIA. 
region in which the rains are pretty regular, but they are felt occasionally up to the 
isotherm of 70°, and even beyond. 
When the sea-winds set in on the coasts of Bengal and Orissa in the early spring 
months — winds which I have said are at first restricted to the lowest stratum of the 
atmosphere — they bring the vapour, which is precipitated as the spring rains, chiefly 
in the form of storms. It is at the beginning of this season that hail-storms are most 
frequent. In Lower Bengal two or three such storms generally occur in the month of 
March, and may be traced to the meeting of the land- and sea-winds, and probably to 
the dynamic cooling of ascending currents*. The heavier rains of Eastern Bengal are 
determined probably by the character of the country — hills for the most part covered 
with forest, and with marshes extending up to their foot. The evaporation is such as 
to keep the ground and superincumbent air lower in temperature and more humid than 
anywhere in Western Bengal. 
In the rains as well as in the hot weather the winds are checked on reaching the 
coast-line, as is evident from the great difference in the mean diurnal movement of the 
air at Saugor Island and Calcutta ; and there must accordingly be an ascending stream 
or eddy, which causes a large precipitation of the vapour within the first few miles 
bordering the coast. Of this the rainfall Table and chart bear evidence. 
The strip of elevated country south of the Ganges, in which (it would appear from 
the few registers that have been kept in this tract) the rainfall averages more than 
50 inches, coincides with the trough of low pressure described at page 604 and indicated 
on the charts for the summer months, especially May and August. It coincides also 
approximately with the line separating the westerly monsoon current of Central India 
from the easterly monsoon of the Ganges valley. 
The Central Provinces to the south of the Satpooras, and even for some distance to 
the north of that chain, receive their rains wholly from the west coast. Much of this 
country is very hilly, but it is not all of this character ; and the numerous feeders of the 
Godavery drain a system of plains, wdiich have a mean elevation of less than 1000 feet 
above the sea, and fall away to the south-east. Yet the rainfall is here heavier than on 
the Deccan plateau nearer the Ghats, which must of course be crossed by the rain- 
bearing winds, excepting such portions as may pass up the valleys of the Taptee and 
Nerbudda. This appears anomalous ; but I think the explanation may be found partly 
in the facts to which General Strachey drew attention in the paper I have before 
referred to (page 596). He there showed that the distribution of vapour vertically in the 
atmosphere, on the hypothesis of independent atmospheres of dry air and water-vapour, 
is inconsistent with the known ratio of temperature decrement with elevation, inasmuch 
as such a distribution would require the existence at comparatively moderate heights of 
* The storms of this time of year are well known as nor’-westers. They are generally accompanied by 
violent electrical discharges, and the barometric column invariably rises rapidly on their approach, sometimes 
to the extent of 0-1 inch ; so that, on looking back through a series of diurnal barometric curves, it is easy to 
detect these days -on which storms have occurred. They occur most frequently about 5 or 6 in the afternoon. 
