esterly gales are to be met
with, by help of which five hundred or a thousand miles of lost
distance are speedily made up, and the rest of the passage secured.

In those regions lying beyond the southern tropic westerly winds
prevail during the greater part of the year, exactly as we find on
this side of the northern tropic. In the southern hemisphere, and far
from the land, the wind may be said to blow from the westward almost
as steadily as the Trades do from the eastward. The great object,
therefore, for an outward-bound ship is to get far enough south to
ensure this fair wind. Beyond the latitude of 30 deg., and as far as 40 deg.,
this purpose will generally be answered.

We are sufficiently familiar in England with the fact of westerly
winds prevailing in the Atlantic. From a list of the passages made by
the New York sailing packets across the Atlantic, during a period of
six years, it is shown that the average length of the voyage from
Liverpool to America, that is, towards the west, was forty days; while
the average length of the homeward passage, or that from west to east,
was only twenty-three days. And it may fix these facts more strongly
in the recollection, to mention that the passage-money from England to
America (in the days of sailing packets) was five guineas more than
that paid on the return voyage.

This prevalence of westerly winds beyond the tropics is readily
explained by the same reasoning which has been applied to the Trades
blowing within them. The swift moving air of the torrid zone, on being
rarefied and raised up, flows along towards the poles, and in a
direction from the equator, above the cooler and slower-moving air,
which, as I have already described, is drawn along the surface of the
earth from the temperate regions beyond the tropics. When the rarefied
equatorial air has travelled some thirty or forty degrees of latitude
along the upper regions of the atmosphere towards the poles it becomes
cooled, and is ready to descend again, between the latitudes of 30 deg.
and 60 deg., to supply the place of the lower air, drawn off towards the
equator by the Trade-winds. But this partially-cooled air falls on a
part of the earth's surface which is moving much more slowly towards
the east, in its diurnal rotation, than the air which has descended
upon it, and which is still impressed with a great proportion of its
eastern velocity due to the equatorial parallels of latitude, where it
was heated a