.RELATION TO THE DISTRIBUTION OE BAROMETRIC PRESSURE. 
339 
These instances abundantly prove the frequent occurrence of the condition described 
—the wind blowing from a place of low pressure to one where the pressure is slightly 
higher; but it may be objected that the places enumerated probably happen to lie 
nearly on an isobaric line, while the wind blows almost parallel to it, so that, if the 
slight disturbances of the true wind direction due to local causes were eliminated, 
there would be no anomaly to explain. The answer to this is that, at the season under 
consideration, the stations enumerated lie near the middle of a very large area of 
uniform low pressure (see Plate 19), while the winds are the strongest and steadiest of 
the year. It may be added, also, that near the equator the wind does not blow 
parallel to the isobars, even over the sea, but makes an angle of two or three points 
with them ; whilst at inland stations, where the friction coefficient is greater, the 
angle must be still greater, as Femiel has pointed out in his works on the movements 
of the atmosphere. The charts prepared from the daily telegraphic weather reports 
for India show an average angle of something like 45° between the wind directions and 
the isobars. The characteristic winds of the hot season, therefore, do really blow 
sometimes in opposition to the pressure gradient, and the cause which sets them 
in motion must be sought somewhere else than in differences of pressure at sea-level, 
or rather at the level of the plain over which they blow. 
Since, in these winds, the air-particles are not urged from west to east by any 
considerable difference of pressure at the ground-level, whilst they are retarded by 
friction, and sometimes even by an increasing pressure, as they go eastwards, their 
velocity must be gradually diminished as they approach the Bay of Bengal. This fact 
is familiarly known to residents on the plains of the Ganges. The “ hot winds,” which 
are excessively dry as well as hot—and which, therefore, serve very effectually to 
refrigerate the interiors of dwelling-houses by blowing through wet tatties, or screens 
of fragrant grass, placed in the door and window openings on the windward side — 
seldom extend as far eastwards as Monghyr, in Behar, # and their extinction takes 
place very gradually. It is a matter of extreme difficulty to obtain truly comparable 
observations of wind velocity, owing in part to slight differences in the anemometers, 
but chiefly to the impossibility of ensuring uniform conditions of exposure; but the 
following sets of stations, where the surroundings are as nearly alike as possible, show 
clearly a gradually diminishing velocity as we go eastwards during the hot weather, 
while, at other seasons there is, in some cases, a tendency for the velocity to increase 
as we approach the sea. The figures are taken from the Beport on the Meteorology 
of India for 1884. They represent the averages of many years. 
* For a short time at the hottest hours of the day westerly winds are felt in Bengal, and even in 
Assam, but they do not possess the dryness and gusty character of the winds under discussion, though 
when they blow they are probably due to similar causes. 
2x2 
