The device requires three wires, two for connecting the lamp with the battery, and one for maneuvering the apparatus through a closing of the contact, B.
With Mr. Mareschal's system, bichromate of potassa piles may be utilized in a large number of cases where a light of but short duration is required until the battery is exhausted, without the tedious maneuvering of a winch and without inconvenience. The jack permits of a large number of lightings and extinctions being effected before it becomes necessary to wind up its clockwork movement. This operation, however, is very simple, and may be performed every time the battery is visited in order to see what state it is in.
We regard Mr. Mareschal's apparatus as an indispensable addition to every case of domestic electric lighting in which bichromate of potassa piles are used, and, in general, to all cases where the pile becomes uselessly exhausted in open circuit. It will likewise find an application in laboratories, where the bichromate pile is in much demand because of its powerful qualities, and where it is often necessary to order it from quite a distant point.--_La Nature_.
The remarkable researches and experiments of Professor Hughes clearly show that magnetism is totally independent of iron, and that its molecules, particles, or polarities are capable of rotation in that metal. It would also appear that by reason of the friction between magnetism and iron, the molecules of the latter are only partially moved, such movement being the result of the tendency of iron to retard magnetic change.
I have found that the magnetic molecules also possess inertia, that they are capable of acquiring momentum, and that their rotation continues for a considerable time after the exciting cause of their rotation has ceased.
These facts may be proved in a very evident manner, inasmuch as induced electric currents are generated by this _after_ rotation, which may be made to light incandescent lamps.
In this case the magnetic rotations are produced in an electro magnet by means of alternate currents supplied by alternating Gramme machine.
In order to better explain the action, it will be necessary to refer to a new electro-motor, which was the subject of an article in the _Electrical Review_ of February 19 last. It is of that type of motor in which the field magnet and armature poles are alternately arranged, and which requires a periodical reversibility of magnetism in the armature to cause the latter to revolve, as in the Griscom motor. The insulating strips in the commutator are sufficiently wide to demagnetize the whole of the machine before reversibility in the armature takes place, and this demagnetization sets up a _direct_ induced current, which is caught in a shunt circuit by the aid of a second commutator, which only comes into action when the first commutator goes out.