| "The instrument represented [at the right] is designed
to show that the action between the current and the magnet takes place
equally well when the magnet itself forms the conductor of electricity.
The lower end of the magnet, being pointed, is supported on an agate at
the bottom of a ... cup connected connected under the baseboard with the
[lower] binding screw cup. The upper end [of the magnet] is hollowed out
to receive the wire connected to the [upper cup]; the brass arm supporting
this cup is insulated from the brass pillar... To the middle of the magnet
is fixed a small ivory cistern ..., for containing mercury, into which
dips the end of [a wire projecting from the middle of the magnet]. Thus
the magnet is supported with its north pole downwards, and is free to rotate
around its vertical axis.
On [making connections to the top and middle of the magnet] with the battery, the current will flow through through the upper half of the magnet causing it to rotate rapidly. If [the middle and the bottom] form the connection, the current will traverse the lower half, equally producing revolution of the magnet. Now connect [the top and bottom with the battery, and no motion will result, because the electricity passes through the whole length of the magnet in such a manner that the tendency of one pole to rotate is counteracted by the other to move in the opposite direction. Connect [the middle] with one pole of the battery, and [the ends] both with the other pole. The magnet will now revolve; since the current will ascend in one-half of its length and descend in the other."
| By the time the 1851 edition of the Manual of Magnetism
was published, the Electro-magnet revolving around its own axis had been
added to the set of demonstration apparatus. The text notes that "the battery
current traverses the helix and one half of the bar. As the bar becomes
an electromagnet, it revolves like the [magnet revolving on its own axis],
except that the direction of the rotating is not changed by reversing the
current, since the poles are at the same time reversed. From the power
of the magnet, the motion is very rapid." (pp 220-221)
This instrument is also at Harvard, and cost $7.00. At the same time, the magnet revolving on its own axis cost $6.00.
Other examples of the magnet rotating about its own axis
can be found with electric