RELATION TO THE DISTRIBUTION OF BAROMETRIC PRESSURE. 
343 
and to the value of gravity at latitude 45°. The isobars have been extended across the 
Bay of Bengal by means of observations extracted from ships’ logs, recently reduced 
and tabulated in the Bengal Meteorological Office. The charts given in Plate 19 are, 
therefore, identical with those for the same months attached to Mr. Blanfokd’s paper 
on the Rainfall of India,* except that the observations of one or two stations which 
seemed to me of doubtful validity have been rejected. 
On the chart for January, the resultant wind directions, on the whole, conform to 
the distribution of pressure in accordance with Buys Ballot’s law, but there are some 
exceptions. For example, at Neemuch, in Southern Rajputana, south-westerly winds 
prevail where the law would indicate an excess of easterly components. The chief 
exception is in Northern Bengal, where the winds should be easterly or south-easterly 
according to the law, whereas there is a decided prevalence of north-westerly winds 
as far a,s Chittagong. 
Elsewhere, except on the west coast, where the sea-breezes prevent observations, 
made only in the day time,t from giving the true resultant direction, the prevailing 
wind agrees closely with that given by the law ; when it is borne in mind that, near 
the Equator, the angle between the wind direction and the isobars is larger than in 
higher latitudes. 
In May, while there is close conformity to the law in Southern India, and near the 
coast generally, there is no apparent relation whatever between pressure distribution 
and wind direction over the very large area north of the parallel of 20° and west 
of the meridian of 86°. The greater portion of this area is enclosed by the very 
peculiarly curved isobar of 29 , 60", within which are two distinct areas where 
the pressure is below 29 , 55 // . One of these occupies the upper valley of the Maha- 
nadi, in the eastern part of the Central Provinces, and the other and lai’ger is in 
Upper Sindh and the Bikanir desert. Over these areas bounded by closed curves, and 
across the axis of low pressure connecting them, as well as across the isobar of 29•60" 
which runs along the southern face of the Himalaya, the westerly winds blow without 
interruption as far as Behar and Chutia Nagpur, and, at a higher level, as far as 
Darjiling; whilst the easterly winds, which should prevail, according to the law, at all 
stations north of the low pressure axis, are only felt along the base of the Himalaya 
up to Gorakhpur. These west winds have a southerly component in the Indus Valley 
and Western Rajputana, as well as at most of the Himalayan stations of 6000 or 
7000 feet elevation, whilst, over the rest of the region, they have usually a northerly 
component; but a. glance at the chart for May will show that they are probably all 
stream lines of one continuous atmospheric flow. 
The chart for July shows that the pressure gradients over the whole of India and 
the Bay are much steeper than in the other months, while the usual relation between 
the direction of the wind and the isobars holds good over nearly every part of the 
* ‘Indian Meteorological Memoirs,’ vol. 3. 
t At most stations the observations are made only at 10 a.m. and 4 p.m. 
