s, the first being 13 1/2 hours and the last 10 1/2
hours. The morning minimum should also be less marked than the evening
minimum, and this also is a fact. The effect also should be greater in
the tropics than in high latitudes, which again also obtains; being 1.32
French lines at the equator, and only 0.18 at latitude 70d. Had the
earth no obliquity, the effect would be as the squares of the cosines of
the latitude; but the ratio is diminished by the inclination of the
axis. But there are other variations of the barometer of longer period,
apparently depending on the phases of the moon, but which cannot be
reconciled to the attracting power of the moon as an atmospheric tide;
and Arago concluded that they were due to some _special cause_, of which
the nature and mode of action are unknown. Perhaps this theory will
obviate the difficulty, as although the central vortex comes to the
meridian at the same time as the moon, its effect will be different on
the inferior meridian to what it is on the superior one; whereas the
moon's attraction should be the same on both. That the passage of a
vortex over or near a particular place should affect the barometer, is
too obvious to need explanation, and therefore we may say that the
theory will explain all those varieties both small and great, which have
caused so much speculation for the last fifty years.

TERRESTRIAL MAGNETISM.

In applying the theory to the magnetism of the earth, we must bear in
mind that the earth is probably magnetic by induction, and not in virtue
of its own specific action. The rotation of the surrounding ether, and
the consequent production of a radial stream, calls the ether into
motion within the earth's interior, as well as on the surface; but it
does not follow that the ether shall also enter the earth at its poles
and escape at its equator, for the obliquity of the vortex would
interfere with this result. It is sufficient that this does occur in the
terral vortex immediately surrounding the earth. From late experiments
it is pretty well established that the axial direction of the needle,
(and of other bodies also,) is due to peculiar internal arrangement in
laminae or layers, the existence of which is favorable to the passage of
the magnetic current.

According to the experiments[27] of Dr. Tyndal, it is found that the
magnetism of a body is strongest along the line of greatest density. As,
therefore, the laminae of bodies may be considered plane