THE CALMS. 67 
Among these we particularly notice high chains of mountains, 
the unequal capacity of sea and land in absorbing and re- 
taining heat, which gives rise to sea and land breezes; the 
increasing or diminishing power of the sun in different seasong 
by which the equilibrium of the air is modified in many cour- 
tries, the difference of radiation from a sandy desert or a forest, 
electrical discharges from clouds, &c. &e. 
Although subject to many of these local disturbances, the 
winds generally blow with an astonishing regularity in the 
tropical zone; while in our variable climate the polar and 
equatorial stream are engaged in a perpetual strife, now bring- 
ing us warmth and moisture from the south and west, now cold 
and dryness from the north and east. 
Thus, in the Atlantic and Pacific Ocean we find the trade- 
winds perpetually blowing from the east, the north-east trade- 
wind between 9° and 27° N. lat., and the south-east trade-wind 
between 3° N. lat and 25°S. lat. It was by their assistance that 
Columbus was enabled to discover America, and that the wretched 
barks of Magellan traversed the wide deserts of the Pacific from 
end to end. 
Between these two regions of the trade-winds lies the dreadea 
zone or girdle of the equatorial calms (doldrums), where long 
calms alternate with dreadful storms, and the sultry air weighs 
heavily upon the spirits. 
“Down dropt the breeze, the sails dropt down, 
’Twas sad as sad could be; , 
And we did speak, only to break 
The silence of the sea. 
“ Day after day, day after day, 
We stuck, nor breath, nor motion, 
As idle as a painted ship 
Upon a painted ocean.” 
On their polar limits, the trade-wind zones are again girdled 
with calm belts, the horse latitudes, whose mean breadth is 
from ten to twelve degrees. The boundaries of these alternating 
regions of winds and calms are not invariably the same, on the 
contrary, they are perpetually moving to the north or south, 
aceording to the position of the sun. 
From 40° N. lat. to the pole, westerly winds begin to be 
