egarding the deflection
east and west) might then be represented by a treble link or loop, whose
nodes would vary but little from latitudes 30d and 60d. As it is, it
has, no doubt, its influence, although unimportant, when compared with
the disturbing action of the ethereal vortices.

There is another phenomenon due to the action of the radial stream,
which has given much trouble to the physicist, and which has yet never
been explained. This is the horary oscillations of the atmospheric
pressure which, in some countries are so regular that the time of day
may be ascertained by the height of the barometer. According to
Humboldt, the regularity of the ebb and flow in the torrid regions of
America, is undisturbed by storms or earthquake. It is supposed that the
maxima occur at 9 A.M. and 10 1/2 P.M., and the minima at 4 A.M. and
4 1/4 P.M. From the morning minimum to the morning maximum is,
therefore, five hours; from the evening minimum to the evening maximum
is 6 1/4 hours; from the evening maximum to the morning minimum is 5 1/2
hours, and from the morning maximum to the evening minimum is 7 1/4
hours. Again, these oscillations are greatest at the equator, and
diminish with the increase of latitude.

[Illustration: Fig. 23]

If we suppose the earth's axis perpendicular to the plane of the vortex,
and P the pole in the above figure, and SP the line joining the centre
of the earth and sun, M and m will represent the points in the earth's
equator where it is midday and midnight respectively. The solar stream
penetrates the terral vortex; and strikes the earth's atmosphere along
the lines parallel to SP. The direct effect would be to pile up the
atmosphere at N and n; and therefore, were the earth at rest, the
maximum would be at 6 A.M. and 6 P.M., and the minimum at midday and
midnight; but the earth rotating from N towards M, carries along the
accumulated atmosphere, being more sluggish in its motions than the
producing cause, which cause is still exercised to force it back to N.
From this cause the maximum is now found at K. For a like reason the
minimum at M would be found at L, but on account of the motion of the
earth being now in the same direction as the solar stream, the minimum
is found still more in advance at k; so that, according to the theory,
the interval between the morning maximum and the evening maximum, should
be greater than the interval between the evening maximum and the morning
maximum; and so it i