1884.] H. F. Blanford— The Winter Rains of Northern India. 59 



observations and is also a consequence of the dynamic theory of heat, 

 that the vertical decrease of temperature in a cloud-laden atmosphere is 

 much slower (about one-third) than that in a clear atmosphere. This 

 initial disturbance will suffice then to cause an indraught of air from 

 around, an ascending current is set up, the barometer falls ; warm vapour- 

 laden winds pour in from the South and we have all the conditions of 

 the winter rains. 



If this view be just, the stillness of the atmosphere combined with 

 the pressure of a moderate evaporation must be accepted as the condition 

 which primarily determines the formation of barometric minima and the 

 winter rains of, Northern India. And this stillness is obviously due to 

 the existence of the lofty mountain ranges which surround Northern 

 India, leaving free access to the plains open only to the South. 



Were the Himalayan chain absent and replaced by an unbroken 

 plain, stretching up to the Gobi desert, it is probable that the winter rains 

 of Northern India would cease ; any local evaporation in the Punjab and 

 Gangetic valley would be swept away by strong dry north-east winds 

 blowing from the seat of high pressure, which, in the winter months, 

 lies in Central Asia, and instead of the mild weather and gentle breezes, 

 which now prevail at that season on the Arabian Sea, it would be the 

 theatre of a boisterous and even stormy monsoon, such as is its local 

 equivalent of the China Seas. 



Mr. Eliot thought that Mr. Blanford's paper was a most valuable 

 one. It dealt with a subject of the greatest interest to Indian meteoro- 

 logists. It was moreover one of very considerable difficulty and on 

 which opinions differed greatly. The winter rains in Northern India 

 occurred under entirely opposite conditions to those of the summer or 

 south-west monsoon rains where the lower air current was a sea- current 

 charged with moisture. The winter rains occur during a period when 

 the lower air currents are land winds, and very dry — and advancing from 

 a region of low temperature to one of higher temperature. The rain 

 accompanies disturbances the conditions and features of which are very 

 clearly and fully stated by Mr. Blanford. He points out that Mr. 

 Chambers, Meteorological Reporter to the Government of Bombay, has 

 asserted that these disturbances are due to the passage of barometric 

 depressions from Beluchistan and Afghanistan, and shows that this is in 

 the majority, if not all the instances, not the case. Mr. Blanford's evi- 

 dence establishing that they originate in India is a very valuable point 

 gained, as it localizes the whole phenomenon. Mr. Eliot was not quite 

 certain whether the upper atmospheric current might not have more to 

 do with the phenomena than appeared from the resume of the paper. 

 He looked forward with much interest to the publication of the complete 



