ing
drawn directly towards the equator, to supply the place of the heated
portions raised into the sky. Consequently, at the tropical borders of
both Trades the wind is found to blow very nearly from the east point.

Since the cool air of the temperate and comparatively slow-moving
zones beyond the tropics is thus drawn towards the equator, and comes
successively in contact with parallels of latitude moving faster and
faster towards the east, there must be gradually imparted to it, by
the increased friction, a considerable degree of the increased
rotatory velocity belonging to the low latitudes it has now reached;
that is to say, there will be less and less difference of velocity
between the easterly motion of this temperate air and the easterly
motion of the earth; and, consequently, the wind, as it approaches the
equator, will appear to blow less and less directly from the
eastward. But, while the earth's rotation within the tropics is thus
acting on the slower-moving air which has travelled to it from beyond
the tropics, with increased friction at every successive moment, there
has been no such powerful counteracting influence in operation to
diminish the meridional motion impressed on the air in question; for,
although in proceeding from the tropics towards the equator, the wind
might, at first sight, be supposed to have its speed somewhat lessened
by friction along the earth's surface, the retardation due to this
cause, if there be any at all, must be inconsiderable, compared to
that which affects the motion caused by the difference in the rotatory
velocity of the earth at the different parallels. It must be
recollected, also, that there is a constant demand for fresh air from
the north and south, to occupy the place of the heated and rarefied
air which is raised up in the torrid zone; and this demand being
pretty equal, the motion it produces on the air in the direction of
the meridian must likewise be uniform.

If it be admitted that all the easterly character of the Trade-winds
is due to the difference of velocity between the rotation of the
torrid zone of the earth from west to east, and that of the air
impressed only with the slower rotatory motion to the east of the
temperate zone, it will follow, that, if this difference of velocities
between the earth and the air in contact with it be diminished or
annihilated, the easterly character of these winds will be diminished
or annihilated likewise. At the same t