of the bar to be moved along it towards the other end. During the
time of the pole's motion there will be an incessant change in the
magnetism of the bar, and accompanying this change we shall have an
induced current in the surrounding coil. If, instead of moving the
magnet, we move the bar and its surrounding coil past the magnetic
pole, a similar alteration of the magnetism of the bar will occur, and
a similar current will be induced in the coil. You have here the
fundamental conception which led M. Gramme to the construction of his
beautiful machine. [Footnote: 'Comptes Rendus,' 1871, p. 176. See
also Gaugain on the Gramme machine, 'Ann. de Chem. et de Phys,'
vol. xxviii. p. 324] He aimed at giving continuous motion to such
a bar as we have here described; and for this purpose he bent it into
a continuous ring, which, by a suitable mechanism, he caused to rotate
rapidly close to the poles of a horse-shoe magnet. The direction of
the current varied with the motion and with the character of the
influencing pole. The result was that the currents in the two
semicircles of the coil surrounding the ring flowed in opposite
directions. But it was easy, by the mechanical arrangement called a
commutator, to gather up the currents and cause them to flow in the
same direction. The first machines of Gramme, therefore, furnished
direct currents, similar to those yielded by the voltaic pile. M.
Gramme subsequently so modified his machine as to produce alternating
currents. Such alternating machines are employed to produce the
lights now exhibited on the Holborn Viaduct and the Thames Embankment.

Another machine of great alleged merit is that of M. Lontin. It
resembles in shape a toothed iron wheel, the teeth being used as
cores, round which are wound coils of copper wire. The wheel is
caused to rotate between the opposite poles of powerful
electromagnets. On passing each pole the core or tooth is strongly
magnetised, and instantly evokes in its surrounding coil an induced
current of corresponding strength. The currents excited in
approaching to and retreating from a pole, and in passing different
poles, move in opposite directions, but by means of a commutator these
conflicting electric streams are gathered up and caused to flow in a
common bed. The bobbins, in which the currents are induced, can be so
increased in number as to augment indefinitely the power of the
machine. To excite his electro-magnets, M. Lontin