58 H. F. Blanford — The Winter Bains of Northern India. [March, 



Thus in the cold weather, rain generally begins in the Punjab and 

 later on extends to the N.-W. Provinces, Behar and sometimes to Bengal. 

 As the disturbance travels eastwards, it is followed up by a wave of high 

 barometric pressure, and cool N. W. winds which usually last for a few 

 days after the rain has cleared off. 



The crucial point of the problem of the cold weather rains is, then, 

 how to account for the formation of these occasional barometric depres- 

 sions in a region where the barometer is generally high at this season. 

 It has been suggested by one writer that they travel to as from the West 

 across Afghanistan. This, however, can be only a guess in the dark, for 

 at the time it was made, there were no observatories to the West of India 

 nearer than Bushire, at the top of the Persian Gulf. There is one now 

 at Quetta, and I have examined the registers of this observatory to see 

 if they give any support to the idea, and find that, with the exception of 

 two doubtful instances, they do not. I conclude therefore that in most 

 cases, if not in all, these disturbances originate in India, and their cause 

 is to be sought for in the meteorological conditions of Northern India 

 itself. In some instances, they make their first appearance in Rajputana 

 or Central India, and there can then be no question whatever of their 

 purely local origin. 



Now the region over which the winter rains are more or less regularly 

 recurrent coincides with that in which the relative humidity of the air at 

 this season, instead of diminishing towards the interior of the country, 

 increases with the increasing distance from the coast. In any month 

 between March and December, as we proceed from the coast of Bengal 

 towards the Upper Provinces, the air becomes drier and drier, not only 

 as containing an absolutely smaller quantity of water vapour, but also in 

 virtue of its increased capacity for taking up vapour, owing to its higher 

 temperature. But from December to March, the dryness increases in- 

 land only as far as Behar. Beyond this, although the quantity of vapour 

 in the air remains very nearly the same or even undergoes a slight di- 

 minution, in virtue of the increasing cold, there is an approach to that 

 temperature at which this small quantity of vapour would begin to con- 

 dense, forming cloud or fog ; and it is in the Punjab that, in this sense, 

 the air is most damp. The result is that which our registers show to be 

 the case, viz., that from December to March it is also the most cloudy 

 province. This seems to depend very much on the stillness of the air. 

 The vapour that is always being given off from the earth's surface dif- 

 fuses gradually upwards in the still atmosphere and soon reaches such an 

 elevation that it begins to condense as cloud. When once a moderately 

 thick bank of cloud is thus formed, the equilibrium of the atmosphere is 

 speedily disturbed. It is well known as a fact from Glaisher's balloon 



