. No doubt the space
round every magnet presented itself to his imagination as traversed by
loops of magnetic power; but he was chary in speaking of the physical
substratum of those loops. Indeed it may be doubted whether the physical
theory of lines of force presented itself with any distinctness to his
own mind. The possible complicity of the luminiferous ether in magnetic
phenomena was certainly in his thoughts. 'How the magnetic force,' he
writes, 'is transferred through bodies or through space we know not;
whether the result is merely action at a distance, as in the case of
gravity; or by some intermediate agency, as in the case of light, heat,
the electric current, and (as I believe) static electric action. The
idea of magnetic fluids, as applied by some, or of Magnetic centres of
action, does not include that of the latter kind of transmission, but
the idea of lines of force does.' And he continues thus:--'I am more
inclined to the notion that in the transmission of the [magnetic] force
there is such an action [an intermediate agency] external to the magnet,
than that the effects are merely attraction and repulsion at a distance.
Such an affection may be a function of the ether; for it is not at all
unlikely that, if there be an ether, it should have other uses than
simply the conveyance of radiations.' When he speaks of the magnet in
certain cases, 'revolving amongst its own forces,' he appears to have
some conception of this kind in view.

A great part of the investigation completed in October, 1851, was
taken up with the motions of wires round the poles of a magnet and the
converse. He carried an insulated wire along the axis of a bar magnet
from its pole to its equator, where it issued from the magnet, and was
bent up so as to connect its two ends. A complete circuit, no part of
which was in contact with the magnet, was thus obtained. He found that
when the magnet and the external wire were rotated together no current
was produced; whereas, when either of them was rotated and the other
left at rest currents were evolved. He then abandoned the axial wire,
and allowed the magnet itself to take its place; the result was the
same.[2] It was the relative motion of the magnet and the loop that was
effectual in producing a current.

The lines of force have their roots in the magnet, and though they may
expand into infinite space, they eventually return to the magnet. Now
these lines may be intersected close to the