cipate from the fact that the
declinations are in _contrary directions_ in the northern and southern
hemisphere. This is owing to the ever-varying declination of the sun.
There would be such a line, no doubt, if the axis of the earth were
perpendicular to the plane of the orbit, and the magnetic pole coincided
with the pole of rotation: for then the equator would be such a line.

MAGNETIC STORMS.

But there are also irregular fluctuations in the direction of the
magnetic needle. These depend on the moon, and are caused by the passage
of the vortices over or near to the place of observation. The action of
these vortices is proved to be of variable force, whether arising from
atmospheric conditions, or due to an increased activity of the ethereal
medium throughout the whole system, is at present immaterial. They do
vary, and sometimes the passage of a vortex will deflect the needle a
whole degree. At other times, there are magnetic storms extending over a
great part of the earth's surface; but there is reason to suppose, that
the extent of these storms has been over estimated. Thus, on the 25th of
September, 1841, a magnetic storm was observed in Toronto, and at the
same time there was one felt at the Cape of Good Hope. There is no great
mystery in this. If we suppose the axis of the central vortex, for
instance, to have passed Toronto in latitude 43d 33' north, in ordinary
positions of the moon, in her orbit, the southern portion of the axis
would be in 33d or 34d south latitude, and consequently would have
passed near the Cape of Good Hope on the same night. Now, we certainly
could not expect the northern portion of the vortex to be intensely
active, without the southern portion being in the same state of
activity. That this is the true explanation is proved by magnetic storms
in the same hemisphere being comparatively limited in extent; as,
according to Gauss and Weber, magnetic storms which were simultaneously
felt from Sicily to Upsala, did not extend from Upsala to Alten. Still
it would not be wonderful if they were felt over a vast area of
thousands of miles as a consequence of _great_ disturbance in the
elasticity of the ether in the terral vortex; as the solid earth must be
permeable to all its motions, and thus be explicable on the general
principles we have advanced.

But besides these variations which we have mentioned, there are changes
steadily going on, by which the isodynamic, isogonic and isoclinic li