ir
vast nautical value, in fact, as well as philosophical curiosity,
turns mainly on their uniformity, which, in spite of all the
fluctuations alluded to, gives them a very distinctive character.

Dr. Young and Hadley, the great authorities on the subject, are both
wrong in their conclusions.[3] Where Hadley obtains his "experience"
he does not tell; but certain it is, that no sailor who ever crossed
the equinoctial line could possibly have furnished him with two of his
principal statements. The Trades are not strongest near the equator,
as he states, nor when they reach that district do they blow along it,
or in a parallel direction, but almost always at right angles to it.

If the earth had no motion on its axis, but were surrounded as at
present with an atmosphere, and if the sun moved round and round it
exactly above the equator, without varying his declination, the
following effects would ensue: That portion of the earth lying, say
thirty degrees, on each side of the equator, being more exposed to the
action of the sun than those further from it, would become much
warmer; while the superincumbent air, being greatly heated by the
contact, would expand, or become specifically lighter, and would
consequently rise. The adjacent air, both on the north and south,
being cooler, and, of course, heavier, would rush in to supply the
place of the heated air. This air coming from the regions beyond the
tropics would, in its turn, be heated, and rise on reaching the warmer
equatorial regions, giving place to a fresh supply, which, it is easy
to see, must be furnished by the descent of that portion of air
formerly heated at the equator, raised into the cold regions of the
sky, and forced into a regular circuit by fresh elevations of heated
air. All these and many other interesting results are clearly
developed in Daniell's Meteorological Essays, a book which every one
at all interested in such inquiries will find it advantageous to
study. The first edition of this work was published in 1823, some
years after these speculations had been forced upon my notice by a
long course of service between the tropics.

It will be understood, that, as long as we imagine the globe at rest
while this circulation is going on, the course of the lower air along
the surface would be directly towards the equator, from due north in
one hemisphere, and from due south in the other; while in the upper
regions the currents would follow the opposite di