ter. The letters S and N designate the
south and north ends of the needle when affected merely by terrestrial
magnetism; the end N is therefore the marked pole (44.). The whole
instrument was protected by a glass jar, and stood, as to position and
distance relative to the large magnet, under the same circumstances as
before (45.).

88. All these arrangements being made, the copper disc was adjusted as in
fig. 7, the small magnetic poles being about half an inch apart, and the
edge of the plate inserted about half their width between them. One of the
galvanometer wires was passed twice or thrice loosely round the brass axis
of the plate, and the other attached to a conductor (86.), which itself was
retained by the hand in contact with the amalgamated edge of the disc at
the part immediately between the magnetic poles. Under these circumstances
all was quiescent, and the galvanometer exhibited no effect. But the
instant the plate moved, the galvanometer was influenced, and by revolving
the plate quickly the needle could be deflected 90 deg. or more.

89. It was difficult under the circumstances to make the contact between
the conductor and the edge of the revolving disc uniformly good and
extensive; it was also difficult in the first experiments to obtain a
regular velocity of rotation: both these causes tended to retain the needle
in a continual state of vibration; but no difficulty existed in
ascertaining to which side it was deflected, or generally, about what line
it vibrated. Afterwards, when the experiments were made more carefully, a
permanent deflection of the needle of nearly 45 deg. could be sustained.

90. Here therefore was demonstrated the production of a permanent current
of electricity by ordinary magnets (57.).

91. When the motion of the disc was reversed, every other circumstance
remaining the same, the galvanometer needle was deflected with equal power
as before; but the deflection was on the opposite side, and the current of
electricity evolved, therefore, the reverse of the former.

92. When the conductor was placed on the edge of the disc a little to the
right or left, as in the dotted positions fig. 9, the current of
electricity was still evolved, and in the same direction as at first (88.
91.). This occurred to a considerable distance, i.e. 50 deg. or 60 deg. on each
side of the place of the magnetic poles. The current gathered by the
conductor and conveyed to the galvanometer was of the same ki