re of any distinct
_facts_ which authorize the conclusion that it is in a particular state.

* * * * *

243. In considering the nature of the cause assigned in these papers to
account for the mutual influence of magnets and moving metals (120.), and
comparing it with that heretofore admitted, namely, the induction of a
feeble magnetism like that produced in iron, it occurred to me that a most
decisive experimental test of the two views could be applied (215.).

244. No other known power has like direction with that exerted between an
electric current and a magnetic pole; it is tangential, while all other
forces, acting at a distance, are direct. Hence, if a magnetic pole on one
side of a revolving plate follow its course by reason of its obedience to
the tangential force exerted upon it by the very current of electricity
which it has itself caused, a similar pole on the opposite side of the
plate should immediately set it free from this force; for the currents
which tend to be formed by the action of the two poles are in opposite
directions; or rather no current tends to be formed, or no magnetic curves
are intersected (114.); and therefore the magnet should remain at rest. On
the contrary, if the action of a north magnetic pole were to produce a
southness in the nearest part of the copper plate, and a diffuse northness
elsewhere (82.), as is really the case with iron; then the use of another
north pole on the opposite side of the same part of the plate should double
the effect instead of destroying it, and double the tendency of the first
magnet to move with the plate.

245. A thick copper plate (85.) was therefore fixed on a vertical axis, a
bar magnet was suspended by a plaited silk cord, so that its marked pole
hung over the edge of the plate, and a sheet of paper being interposed, the
plate was revolved; immediately the magnetic pole obeyed its motion and
passed off in the same direction. A second magnet of equal size and
strength was then attached to the first, so that its marked pole should
hang _beneath_ the edge of the copper plate in a corresponding position to
that above, and at an equal distance (fig. 37.). Then a paper sheath or
screen being interposed as before, and the plate revolved, the poles were
found entirely indifferent to its motion, although either of them alone
would have followed the course of rotation.

246. On turning one magnet round, so that _opposite_ poles