THE TRADE-WINDS 
summer, when they are most directly exposed to the rays of the sun. 
Over the ocean the region of high temperature and low pressure 
forms a belt, towards which winds blow more or less from the north 
and south. The direction of these winds 18, however, modified by 
the rotation of the earth, in consequence of which these winds, 
<nown as the trade-winds, blow more or less from the east, in some 
parts of the Pacific almost directly from the east, as, for example, 
where, in the language of Sir Thomas Browne, * sailing from Lima to 
Manilla . . . you may fasten up the rudder and sleep before the 
wind.” It is important, therefore, to observe and constantly to bear 
in mind that over a great width of the ocean in low latitudes extend - 
Ing on both sides far beyond the tropics, there is a strong tendency 
for the winds to blow away from the west sides of the continents and 
towards the east sides of the continents. The position of this wide 
belt, or rather of the two wide belts separated by an intermediate belt 
of calms corresponding to that of lowest pressure, is not constant. It 
moves north and south with the sun, along with the whole system of 
atmospheric pressures dependent on the height of the sun above the 
horizon. Wherever and whenever the trade-winds blow, however, 
they have a certain effect in mitigating the temperatures of the 
regions exposed to them. 
53. Outside of the trade-wind region there is normally in the 
#inter months an area of low pressure in the North Atlantic to the 
north of 60° N., and in the North Pacific a similar area more to the 
south. Towards each of these the winds tend to blow, but in con- 
sequence of the rotation of the earth not directly, but in great spirals 
in which the direction of movement is opposite to that of the hands of 
a watch. Hence south-westerly, and consequently warm, winds prevail 
at this season on nearly all the west coasts of Europe and a large part 
of the west coast of America, while northerly, and hence cold, winds 
prevail on the opposite coasts, that 1s, on the east coast of North 
America, and the east coasts of northern Asia. The contrast between 
the temperatures of these coasts in corresponding latitudes is another 
great fact constantly to be borne in mind, as well as the fact that the 
denefit of the relatively high winter temperatures is carried by the 
winds a greater or less distance inland. Warm ocean currents flowing 
0 the same direction as these winds blow help to maintain their 
temperature, but it is to be observed that without the winds these 
currents would have no effect whatever on the temperature over the 
land. In the summer months the area of low pressure still exists in 
the North Atlantic, so that in that period also south-westerly winds 
prevail, though not so strongly on the west European coasts. In the 
North Pacific during the summer months an area of low pressure can 
scarcely be said to exist. In the southern hemisphere outside of the 
irade-wind belt the conditions are greatly altered by the fact that the 
amount of land is very small. It is enough to say that there the 
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