of the currents will be generally the same, being modified only by the
coaction which can take place between the particles, now that they are in
metallic contact.

120. Now that the existence of these currents is known, Arago's phenomena
may be accounted for without considering them as due to the formation in
the copper, of a pole of the opposite kind to that approximated, surrounded
by a diffuse polarity of the same kind (82.); neither is it essential that
the plate should acquire and lose its state in a finite time; nor on the
other hand does it seem necessary that any repulsive force should be
admitted as the cause of the rotation (82.).

121. The effect is precisely of the same kind as the electromagnetic
rotations which I had the good fortune to discover some years ago[A].
According to the experiments then made which have since been abundantly
confirmed, if a wire (PN fig. 26.) be connected with the positive and
negative ends of a voltaic buttery, so that the positive electricity shall
pass from P to N, and a marked magnetic pole N be placed near the wire
between it and the spectator, the pole will move in a direction tangential
to the wire, i.e. towards the right, and the wire will move tangentially
towards the left, according to the directions of the arrows. This is
exactly what takes place in the rotation of a plate beneath a magnetic
pole; for let N (fig. 27.) be a marked pole above the circular plate, the
latter being rotated in the direction of the arrow: immediately currents of
positive electricity set from the central parts in the general direction of
the radii by the pole to the parts of the circumference _a_ on the other
side of that pole (99. 119.), and are therefore exactly in the same
relation to it as the current in the wire (PN, fig. 26.), and therefore the
pole in the same manner moves to the right hand.