down to the surface of the earth beyond the calms of the tropics,
and that it thence proceeds with an increasing eastward motion,
appearing in our northern hemisphere as the prevailing northeastward
winds. Approaching the poles with a spiral motion, the air there
rises, according to this hypothesis, in a vortex, and returns toward
the equator in the upper atmosphere, gradually acquiring a westward
motion; till, returning to the tropics, it is again brought down to
the earth, and thence proceeds, with a still increasing westward
motion, as the trade-winds. At the equator the air rises again, and,
according to Lieut. Maury, crosses to the other side, and proceeds
through a similar course in the other hemisphere.

The rising of the air at the equator is supposed to cause the
equatorial rains; and the drought of the tropics is also explained
by that descent of the air, in these latitudes, which this
hypothesis supposes.

Now although this hypothesis explains the phenomena, it has still
met with great opposition. The motions which Lieut. Maury supposes
can hardly be accounted for without resorting, as is usual in such
cases, to electricity or magnetism,--to some occult cause, or some
occult operation of a known cause. Moreover, it has been difficult
for the mechanical philosopher to understand how the winds manage to
cross each other, as Lieut. Maury supposes them to do, at the
equator and the tropics, without getting into "entangling alliances."
If this hypothesis were advanced, not as a physical explanation of
the phenomena, but, like the epicycles and eccentrics of Ptolemy,
"to save the appearances," its ingenuity would be greatly to its
author's credit; but, like the epicycles and eccentrics, though it
represents the phenomena well enough, it contradicts laws of motion,