At Proceedings of the Asiatic Society. [ Fue. 
- throughout India would have for science generally, and as means 
for the solution of this question in particular, under careful analy- 
sis and comparison? Every condition affecting the supply of 
vapour through the action of heat at the earth’s surface, is a cause 
which influences the local atmospheric pressure in a direction con- 
trary to that in which the heat alone operates, and we find such 
conditions existing in notable opposition of extreme throughout 
the countries which are immediately subject to Her Majesty’s In- 
dian Government. Need I contrast the maritime and the conti- 
nental tracts, the deltas and the inland plateaux, the plains and 
the mountain peaks which I may say are paired against each 
other from the Himalayas to Point de Galle (more than the breadth 
of the northern tropic) and from the west coast of Malabar to the 
Salween. In truth we possess in India almost unrivalled opportu- 
nities for examining and analysing the atmospheric column in all 
its parts. 
Doubtless the daily periodic changes of pressure, by their very 
nature, are ineffective to cause anything more than very limited 
oscillatory local movement of air masses. These movements, how- 
ever, are not always insignificant in themselves, as for instance the 
land and sea breezes of our coast districts, the winds on the outer 
flanks of mountain ranges and in mountain valleys and the diurnal 
modifications of the Monsoon which we experience in Calcutta. 
But the daily phenomena of this class are especially important, be- 
cause they are both the type and the material of those annual va- 
riations which are serious enough to be the governing forces in 
regard to the winds of this portion of the globe. We may in this 
matter liken the year to one long day with the solstices for mid- 
night and noon. The gradual increase of temperature which takes 
place over the greater part of the earth’s surface from a minimum 
in the winter months toa maximum in the summer months is (as 
in the case of a day of 24 hours and probably for a common reason) 
generally speaking accompanied by a double oscillation of the 
atmospheric pressure. In places of western Europe near the sea, 
where I may remark the source of vapour is unlimited, both sets of 
maxima and minima are I believe invariably strongly marked, the 
summer maximum whichis attributed to the vapour, being commonly 
