104 Weather Charts. [Apeil, 



Meteorological Society, Vol. V, p. 213. On this latter occasion some rain 

 fell in the earlier part of the storm, and before it had quite cooled was ac- 

 companied by a distinctly hot and dry wind, which lasted, however, only for 

 a short time, and was followed, as is usual in Nor' -Westers, by a calm. 



Mr. Blanford said that having regard to all the circumstances of these 

 storms, he could not regard the rise of temperature as due to the influx of 

 a hot surface-wind, but considered it more probable that it was a case of 

 dynamic heating. As Mr. Phear had pointed out at a former meeting of 

 the Society, the strong gusty wind of a Nor'- Wester is probably a portion 

 of the upper Westerly current that strikes down to the earth. Such a 

 mass of air in descending must, according to thermo-dynamic laws, deve- 

 lop 1° of temperature for each 183 feet through which it descends. In 

 rainy storms this heat is probably used up in great part in the evaporation 

 of the accompanying rain, but in storms in which little or no rain occurs 

 during the descent, a part of this heat is retained and causes a rise of the 

 thermometer and a great fall in the humidity of the air. 



Mr. H. F. Blanpoed also exhibited a series of the charts now drawn up 

 in the Meteorological Office, which show the distribution of pressure and 

 temperature, the wind direction and the rainfall at 10 p. M. daily for the 

 whole of India. The two former elements are shown by blue and red lines 

 which respectively represent the isobars for each twentieth of an inch and 

 the isotherms for each 5° of temperature. The series began with October 

 last, and as yet it would be premature to attempt to generalize on the facts 

 they exhibit, but he drew attention to one or two cases of rainfall during 

 the cold weather months, and contrasted them with the charts exhibited 

 on a former occasion, which had been specially drawn up to show the state 

 of things that accompanied the rainfall of the S. W. monsoon. These lat- 

 ter showed that during the S. W. monsoon, barometric minima or cyclones 

 (not of a violent character) were successively formed either in the N. W. 

 corner of Bengal, or over Orissa and the country to the westward, and, 

 in 1875, moved northward or north-westward, carrying the rain with 

 them to the G-angetic valley and the Central and Upper Provinces. Dur- 

 ing the season of 1877 they had not followed this latter course, but in many 

 cases had moved towards the north-east, whence the almost entire failure of 

 the rainfall in the N. W. Provinces. 



In the cold weather months, again, the state of things was different. 

 There was a constant tendency to a high pressure in the lower Indus vaUey ; 

 but to a frequent recurrence of low-pressure areas in the Punjab, where it 

 appeared that the rain first fell. This fall was followed by a strong cool 

 current from the North- West, and the rainfall area then receded down the 

 Gangetic valley and in some cases reached Lower Bengal. 



