Faraday, Michael, 1791-1867; Physicists -- Great Britain -- Biography
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 magnet or at a distance from
it. Faraday finds distance to be perfectly immaterial so long as the
number of lines intersected is the same. For example, when the loop
connecting the equator and the pole of his barmagnet performs one
complete revolution round the magnet, it is manifest that all the lines
of force issuing from the magnet are once intersected. Now it matters
not whether the loop be ten feet or ten inches in length, it matters
not how it may be twisted and contorted, it matters not how near to the
magnet or how distant from it the loop may be, one revolution always
produces the same amount of current electricity, because in all
these cases all the lines of force issuing from the magnet are once
intersected and no more.
From the external portion of the circuit he passes in idea to the
internal, and follows the lines of force into the body of the magnet
itself. His conclusion is that there exist lines of force within the
magnet of the same nature as those without. What is more, they are
exactly equal in amount to those without. They have a relation in
direction to those without; and in fact are continuations of them....
'Every line of force, therefore, at whatever distance it may be taken
from the magnet, must be considered as a closed circuit, passing in some
part of its course through the magnet, and having an equal amount of
force in every part of its course.'
Public-domain text, read in full here on John Shaqi.
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