1873.] H. F. Blanford— On the Climate of Bengal 183 



from recent investigations, that, however well known at sea, the character 

 and origin of the monsoons on the land have been very generally misunder- 

 stood. The monsoons are not two undivided currents, flowing to and from 

 Central Asia during about equal periods of the year ; but appear rather to 

 consist, at each period, of at least two principal currents, the one tending 

 to or from Northern India, the other to or from the interior of China ; and 

 there are probably other minor currents originating or terminating at other 

 centres. The Indian branch of the winter monsoon originates in the plains 

 of the Panjab, the Gangetic valley, and the uplands of Central India ; also in 

 upper Asam ; and blows as a very gentle wind towards the two great 

 bays that wash the East and West coasts of the Peninsula. During this 

 season, a Southerly wind prevails steadily on the Himalaya at heights above 

 6000 or 8000 feet, descending lower on the Western than on the Central 

 part of the range. This appears to be the upper return current of the win- 

 ter monsoon, and corresponds to the anti-trade of the trade wind 

 region. It descends on the plains of Upper India, where the atmos- 

 phere is characteristically calm at this season ; and brings the winter 

 rains. It is less frequently felt in Lower Bengal, where the wind is 

 variable from North and North- West ; but to the eastward in Kachar, 

 southerly winds are very prevalent at the winter season. In Northern 

 India the two branches of the northerly monsoon appear to diverge towards 

 the opposite coasts, from a line characterized hj a ridge of higher mean 

 barometric pressure, which passes from the Panjab through Banaras to 

 Katak. This monsoon ceases on the coast line of Bengal in the month of 

 February, when in the lower atmosphere, sea winds set in. At first these 

 are restricted to the immediate neighbourhood of the coast ; but as the sea- 

 son advances and the heat of the interior plains rises under the influence of 

 the returning sun, they penetrate further and further inland, and are drawn 

 from greater distances at sea. In the interior of India, the wind becomes 

 more Westerly, and blows towards Lower Bengal and Chutia Nagptir, not 

 as a steady current, but as day winds, which in April and May are highly 

 heated by the parched and heated soil, and constitute the well known hot 

 winds of those months. Where these two currents meet, the thunder-storms 

 well known as North- Westers are generated. Like the thunder-storms of 

 Europe and the dust-storms of the Panj.ib, they are due to convection cur- 

 rents ; and in Bengal owe their prevailing movement from the West or North- 

 West quarter to the strength of the land wind, which maintains its course 

 in the upper atmosphere above the opposite sea-wind which is felt at the 

 land surface. At this time the N. W. wind continues to blow unsteadily in 

 the South of the Bay ; but calms are not infrequent ; and it is not till June 

 that the Southerly winds of the bay become continuous with the South East 

 Trades of the South Indian Ocean, and that the South West monsoon, pro- 



