1884.] Uains of Nortliem India, 3 



the opposite season. It extends from Upper Sind across Rajputana and 

 the Central India plateau to Cliutia Nagpur ; the pressure along this 

 axis declining, more or less irregularly, from N. W. to S. E. To the 

 north of this ridge, a trough of relatively low pressure on the Gangetic 

 plain separates it from the higher pressure along the foot of the Hima- 

 laya, and, in most years, the pressure in the Punjab is somewhat lower 

 than that of Western Rajputana. On the other hand, to the south of 

 this axis, the pressure falls gradually down to Cape Comorin and Tra- 

 vancore ; being, however, considerably higher on the east than on the 

 west coast of the peninsula. In fact, the isobars run down the peninsula 

 almost parallel with the west coast. The low pressure area which runs 

 down the west coast of the peninsula is prolonged to the north, up the 

 Gulf of Cambay, producing a northward bend in the isobars of that 

 region very similar to that shewn by them in the summer monsoon, 

 but with reversed gradients. 



Hence the cold weather distribution of pressure may be not inaptly 

 described as a reversal of that which characterizes the summer mon- 

 soon ; but, in the first place, the barometric differences between the 

 extremes, and therefore the gradients effective in producing the monsoon 

 current, are less than half as great, and, in the second place, the axis 

 of high pressure across Northern India lies further south than its 

 opposite in the summer monsoon. It lies well across the middle of the 

 plateau to the south of the Ganges, instead of following the course of 

 the river, or, as not unfrequently happens in the case of the summer 

 trough of depression, somewhat to the north of it. Thus, both in 

 summer and winter, low pressure tends to prevail in some part or other 

 of the Gangetic valley and the Punjab ; but in the summer the gradient 

 declines towards the N. W., in the winter, to the S. E. 



There is reason to believe that this normal distribution of pressure 

 is restricted to the lower strata of the atmosphere, that is to say, to the 

 stratum less than 7,000 feet in vertical thickness, measured from the 

 sea-level. Thus, for instance, a row of stations on the plains of the 

 Punjab and Ganges, ranging from Peshawar down to Purneah, shews 

 a small, but decided, fall of pressure from I^. W. to S. E., when all the 

 mean readings are reduced to their equivalent values at the sea-level. 

 But if the mean pressures of the hill- stations, Murrec, Chakrata, and 

 Darjeeling (all of which are between 6,000 and 7,000 feet, or a little 

 over the latter elevation), be reduced to a common level of 7,000 feet, 

 the gradient at that elevation is found to be slightly, but distinctly, re- 

 versed ; Darjeelingy the easternmost station, shewing the highest pressure. 



