394 
VOYAGE OF THE POTOMAC. 
[June, 
north, when the southwest monsoon sets in; and often, on the 
south part of the coast, with great violence. 
This change, or reflux of air, appears to be put in motion by 
the same means as that which comes from the opposite quarter — 
for as the sun's altitude increases daily in the northern hemisphere, 
the extensive body of land in' the northeast part of Asia becomes 
hotter than the ocean ; and, consequently, a degree of rarefaction 
will be produced over that portion of the continent, while, at the 
same season, an immense body of cold air will come from the In- 
dian Ocean and the continent of Africa, in the southern hemi- 
sphere, to restore the equilibrium. 
The principal tracts of land of different temperatures on the 
two continents, bearing very nearly northeast and southwest from 
each other, will therefore become the two opposite extreme points 
of rarefaction and condensation ; and necessarily be the imme- 
diate causes of the northeast and southwest monsoons. 
The southwest monsoon blows with great strength on the Mal- 
abar coast, in April, May, June, and July ; but owing to a range 
of mountains, it is not felt with much violence on that of Coro- 
mandel, except far south. Both the northeast and southwest 
monsoons blow at first in fresh gales ; but neither of them in- 
creases to a hurricane. From natural causes, the one must die 
away before the other sets in. Hurricanes most frequently, 
indeed, it might be said always, occur near large bodies of land. 
In the Mosambique Channel, the monsoons correspond nearly 
with those on the Malabar coast ; if not in their commencement, 
at least in their duration. The southwest beginning in April, and 
continuing till November : the northeast then succeeding, and 
continuing until April. But the southwest monsoon in this 
channel is the fair season, and the wind varies sometimes towards 
the southeast and east-southeast on either coast, about the middle 
of November, when there are also generally regular land and 
seabreezes. ' ■ - 
The northeast monsoon begins early in November, near the 
Comoro Islands and the north end of Madagascar; but seldom 
extends beyond San Augustine Bay, which is near the south 
tropic. Towards the Eastern Isles, the tradewind prevails over 
the Indian Ocean, from latitude eleven to twenty-eight south; 
while to the south and east of Java and Sumatra, northwest and 
