1904.] C. Little — The recent excessive heat in Bengal, 9 



thunderstorms of the past hot season have, with a few exceptions which 

 occurred in the latter half of June, approached Calcutta from the west 

 instead of from the north-west, and have passed away eastward instead 

 of south-eastward. I have no hesitation in stating that, so far as Cal- 

 cutta is concerned, although there have been a great many thunder- 

 storms, there has not been a single nor'wester, if the scientific meaning 

 of that term of popular origin, be the same as its ordinary meaning. 



The main assumption which I make towards explaining the exces- 

 sive heat of April and May is that the upper air-current across the 

 western border of the province of Bengal was westerly instead of north- 

 westerly. This assumption is based upon the observations of cloud and 

 thunderstorms mentioned in the previous paragraphs, and receives but 

 little support from the ground level observations. 



There is another assumption which I must make, which is of the 

 nature of an inference from the previous assumption, and so far as I am 

 aware is not supported by any direct evidence, because I have no informa- 

 tion regarding the upper air movement except for Calcutta. The as- 

 sumption is that the upper westerly current is warmer than if it had been 

 from the north-west. If a line be drawn north-west from Calcutta on 

 a map it will be seen that as the crow flies we are only 400 miles from 

 the Himalayas. Allowing 20 miles an hour as the velocity of the upper 

 current (possibly an under estimate) it may be stated that the air which 

 passes over Calcutta from the north-west, may 20 hours before have 

 been, the whole or part, in the cool region of the Himalayas. With a 

 westerly current, on the other hand, there has been no cool region to pass 

 over. Instead there have been the hot plains of Central India, and the 

 air of the upper current has during its passage been steadily becoming 

 warmer by convection from the lower layers daily raised to a high 

 temperature by the hot ground surface. 



Still another assumption is required, but not one made by me. It 

 rests on the highest meteorological authority, and I give below its ex- 

 pression, as the idea of a well-known European Meteorologist in the 

 words of an equally well-known American Meteorologist. *' Summer 

 hot waves are explained as stagnant masses of air in which heat gradu- 

 ally accumulates at the ground and then increases to a great height." 

 The assumption involved is that there is a more or less stagnant mass of 

 air associated with hot summer waves. The question, therefore, is, if the 

 winds are westerly in the western districts of Bengal, where is the stag- 

 nant air which meteorological authorities appear to require ? My opin- 

 ion, for some years now, has been that during the hot weather months 

 a very gradual change takes place over Assam and Bengal, and that a re- 

 gion of comparative calm in the upper air is over East Bengal in the 

 J. II. 2 



