REPORT ON ATMOSPHERIC CIRCULATION. 61 



the coasts laden with the moisture of the oceans they have crossed, the result being 

 the large rainfall of southern and eastern Asia. The heaviest of these rains are where 

 mountain ranges lie across the path of the monsoon, and they penetrate farthest inland 

 where the river valleys lie approximately in the course of the monsoon. 



The July isobars of India are of more than ordinary interest, implying, as they do, 

 the utmost practical advantages to the empire. From Cutch southward pressure is 

 everywhere higher in the west than in the east of the same latitudes, represented by 

 the south-easterly slant of the lines as they cross India. The difference is about half a 

 tenth of an inch, and the same difference also holds good in Ceylon. The consequence 

 of this peculiarity in the distribution of the pressure is that the summer monsoon blows 

 more directly from the ocean than would have been the case if the isobars had lain due 

 west and east. A much more important consequence, however, follows from the 

 location of the region of least pressure in the valley of the Indus, so that in the valley 

 of the Ganges, and in the north of India generally, pressure diminishes steadily from 

 east to west, — from Assam, up the Ganges, and westward to Jacobabad on the Indus. 

 The inevitable result of this inversion in the manner of the distribution of the pressure 

 is that the winds are no longer south-westerly, but they become southerly over the Bay 

 of Bengal, and thereafter deflected into E.S.E. winds blowing up and filling the whole 

 valley of the Ganges, and distributing in their course a generous rainfall over this 

 magnificent region. If winds there had been south-westerly, the rainfall would have 

 been meagre and inadequate, owing to the intervention of the Western Ghauts between 

 the sea and the Ganges. 



It will be observed that the low-pressure system of Asia and the anticyclonic 

 system of high pressure of the Atlantic are connected by what is virtually an unbroken 

 broad belt of westerly winds over Europe and western Asia, bearing with them much 

 vapour from the Atlantic, to which is due the summer rainfall of this part of the old 

 continent. As they advance farther into Asia they take a northerly direction as they 

 turn towards and blow round upon the region of low pressure in the Punjaub. Since, 

 as they assume a northerly direction they blow into hotter regions, it follows that 

 rain ceases to fall, and the climates are among the driest and hottest anywhere on 

 the earth. 



It also follows that Japan is one of the more highly favoured regions as regards its 

 rainfall, depending as it does on the large extent of the Pacific to the south-east, over 

 which the summer monsoon must blow before reaching the Japanese coasts. 



The same principles are illustrated by the direction of the prevailing winds and 

 distribution of the rainfall over and around the more restricted area of low summer 

 pressure in North America. On the west side of this low-pressure area the Pacific anti- 

 cyclone closely presses with its crowded isobars and arid northerly winds ; whilst on 

 the east side lies the higher pressure with its more open isobars and moist southerly 



