s last case the magnetic equator is not a great
circle, neither can we suppose its effects to be an accumulation of a
fluid which is imponderable at points 90d from the plane passing through
the centre of the earth and sun, and coincident with the plane of the
central meridian, and a depressing effect on that meridian. Its precise
influence must be, from the nature of the cause, to deflect the circular
current towards the poles, in places less than 90d from the meridian,
and a contrary effect must be produced in places greater than 90d from
the meridian. Let us assume, for argument's sake, that the magnetic
poles of the earth correspond to the poles of rotation, the parallels of
latitude will, therefore, represent the ethereal currents circulating
around the globe. Now, at sunrise, the radial stream of the solar vortex
is tangential to the surface, and, therefore, can produce no change in
these currents. As the sun ascends say about 8 or 9 A.M., the radial
stream striking only the surface of the earth perpendicularly in that
place where the sun is vertical (which we will suppose at the equator),
streams off on every side, as the meridians do from the pole, and the
circles of latitude (that is the ethereal currents) being parallel to
the equator, they are met by the radial stream obliquely, and deflected
towards either pole. By this deflection they are no longer at right
angles to the meridians. But, from the principle of reaction above
noticed, the magnetic meridians will place themselves at right angles to
the current, or, in other words, the magnetic pole will change its
position on the surface of the earth with respect to that particular
place. But, in other parts of the world, the meridians are in opposite
phases at the same instant of absolute time; therefore, the magnetic
poles are not points, but wide areas enclosing the magnetic poles of all
the countries under the sun. As this conforms to observation, it is
worthy our especial attention, and may be understood by the subjoined
figure, in which the oblique curves represent the course of the
tangential current in the different positions of the sun, the parallel
lines representing the solar radial stream.

[Illustration: Fig. 24]

As the sun gains altitude the action of the radial stream is at a
greater and greater angle to the circular currents, and attains its
maximum at noon, still acting, however, after noon; but seeing that the
circular current possesses a fo