or lac, when _they_ intervene in
the line of magnetic action? The answer to this is at present merely
conjectural. I have long thought there must be a particular condition of
such bodies corresponding to the state which causes currents in metals and
other conductors (26. 53. 191. 201. 213.); and considering that the bodies
are insulators one would expect that state to be one of tension. I have by
rotating non-conducting bodies near magnetic poles and poles near them, and
also by causing powerful electric currents to be suddenly formed and to
cease around and about insulators in various directions, endeavoured to
make some such state sensible, but have not succeeded. Nevertheless, as any
such state must be of exceedingly low intensity, because of the feeble
intensity of the currents which are used to induce it, it may well be that
the state may exist, and may be discoverable by some more expert
experimentalist, though I have not been able to make it sensible.

1729. It appears to me possible, therefore, and even probable, that
magnetic action may be communicated to a distance by the action of the
intervening particles, in a manner having a relation to the way in which
the inductive forces of static electricity are transferred to a distance
(1677.); the intervening particles assuming for the time more or less of a
peculiar condition, which (though with a very imperfect idea) I have
several times expressed by the term _electro-tonic state_ (60. 242. 1114.
1661.). I hope it will not be understood that I hold the settled opinion
that such is the case. I would rather in fact have proved the contrary,
namely, that magnetic forces are quite independent of the matter
intervening between the inductric and the inductions bodies; but I cannot
get over the difficulty presented by such substances as copper, silver,
lead, gold, carbon, and even aqueous solutions (201. 213.), which though
they are known to assume a peculiar state whilst intervening between the
bodies acting and acted upon (1727.), no more interfere with the final
result than those which have as yet had no peculiarity of condition
discovered in them.

1730. A remark important to the whole of this investigation ought to be
made here. Although I think the galvanometer used as I have described it
(1711. 1720.) is quite sufficient to prove that the final amount of action
on each of the two coils or the two cores A and B (1713. 1719.) is equal,
yet there is an effect which