1890.] Relations between the Hills and Plains of Northern India. 39 



plain stations during the fine clear weather which followed 

 the storm. The lowest maximum temperatures were observed 

 in the Punjab on the 9th and in East Bengal on the 12bh. 

 This may be summed up by assuming the eastward passage 

 of a cold wave along the plains of Northern India. 

 2nd. — The lowest night temperatures of the period were registered 

 in the hills on the 6th and 7th during the storm, and in the 

 plains during the fine clear weather which followed in the 

 rear of the storm. Thus the lowest minimum temperatures oc- 

 curred in the Punjab on the 9th, in the North- Western Pro- 

 vinces on the 9th and 10th, in Behar on the 10th and 11th 

 and in Bengal on the 11th and 12th. This further proves the 

 passage of a wave of cold eastwards along the length of the 

 plains of Northern India, at a rate of about 300 miles per 

 diem. 



3rd. — The period immediately following the breaking up of the 

 storm was one of large diurnal range of temperature. The 

 effect of the dry weather which followed in increasing the 

 daily range was shewn most strikingly in Bengal. The daily 

 range at Calcutta increased from 13/4° on the 7th to 25T° on 

 the 12th and at Dacca from 226° on the 7th to 304° on the 

 11th. 



4<th. — There was a large temporary increase in the air motion, which 

 was first shewn at the western stations and extended east- 

 wards. It occurred at the Bengal stations two or three days 

 later than in the Punjab and Western districts of the North- 

 Western Provinces. These winds were the cool westerly winds 

 which followed in the rear of the storm and accompanied the 

 setting in of fine clear dry weather. 

 5th. — The most important change was in the amount of vapour and 

 the humidity of the atmosphere. This was far more marked 

 in Bengal than in the Gangetic area. In Bengal local 

 damp sea winds prevailed during the existence of the cold 

 weather storm, and after it disappeared they were l-eplaced by 

 dry land westerly winds. The humidity at Calcutta decreased 

 from 85 to 33 and at Dacca from 90 to 33 in 24 hours. The 

 aqueous vapour pressure data shew that this was due to a large 

 reduction in the amount of vapour pressure and hence to the 

 displacement of the previous winds by an air current of op- 

 posite characteristics. The amount of vapour in the air at Cal- 

 cutta on the 10th was less than a fourth of that present in it 

 on the 7th. 



