THE ATMOSPHERE. 
89 
southeast trades, and the same causes which operate in CaUfornia 
to prevent rain there, operate in Chih ; only the dry season in one 
place is the rainy season of the other. 
Hence we see that the weatljer side of all such mountains as 
the Andes is the wet side, and the lee side the dry. 
138. The same phenomenon, from a like cause, is repeated in 
inter-tropical India, only in that country each side of the mountain 
is made alternately the wet and the dry side by a change in the 
prevailing direction of the wind. Plate VIII. shows India to be in 
one of the monsoon regions : it is the most famous of them all. 
From October to April the northeast trades prevail. They evap- 
orate from the Bay of Bengal water enough to feed with rains, 
during this season, the western shores of this bay and the Ghauts 
range of mountains. This range holds the relation to these winds 
that the Andes of Peru 133) hold to the southeast trades; it 
first cools and then relieves them of their moisture, and they tum- 
ble down on the western slopes of the Ghauts, Peruvian-like 
(§137), cool, rainless, and dry; wherefore that narrow strip of 
country l)etween the Ghauts and the Arabian Sea would, like 
that in Peru between the Andes and the Pacific, remain without 
rain forever, were it not for other agents which are at work about 
India and not about Peru. The work of the agents to which I 
allude is felt in the monsoons, and these prevail in India and not 
in Peru. 
139. After the northeast trades have blown out their season, 
which in India ends in April (§ 138), the great arid plains of Cen- 
tral Asia, of Tartary, Thibet, and Mongolia, become heated up, 
react upon these northeast trades, turn them back, and convert 
them, during the summer and early autumn, into southwest mon- 
soons. These then come from the Indian Ocean and Sea of Ara- 
bia loaded with moisture, and striking with it perpendicularly upon 
the Ghauts, precipitate upon that narrow strip of land between 
this range and the Arabian Sea an amount of water that is truly 
astonishing. Here, then, are not only the conditions for causing 
more rain, now on the west, now on the east side of this mount- 
ain range, but the conditions also for the most copious precipita- 
tion. Accordingly, when we come to consult rain gauges, and 
to ask meteorological observers in India about the fall of rain, 
they tell us that on the western slopes of the Ghauts it some- 
