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Updated: June 13, 2025
It will be observed that the current excited in the armature also flows through the coils of the electro-magnets, and thus keeps up their strength.
Manufacturers of electro-magnets for telegraphic instruments are very careful to choose the softest iron and thoroughly anneal it; but very few recognize the importance as regards the position of the iron while annealing it under the earth's directing influence. The fact, however, has long since been observed. Dr.
Platinum is non-magnetic. It is simply a soft iron hollow ball, plated with platinum. Whichever set of electro-magnets is energized attracts the ball and by this simple method it is in the power of the operator to let the ball go to red or black as he may wish. Other similar arrangements control the odd or even, and other combinations from other push buttons.
For this reason the system has been given the form of a hexagonal prism, whose faces are formed of flat electro-magnets, A, A, xxx, constituting the inductors. The internal angles of this prism are filled by polar expansions, P, P, xxx, alternately north and south, that thus form in the interior of the apparatus an inscribed cylinder designed to receive the armature.
In 1837, Professor Stratingh, of Groninque, Holland, devised a telegraph in which the signals were made by electro-magnets actuating the hammers of two gongs or bells of different tone; and M. Amyot invented an automatic sending key in the nature of a musical box.
Communication between the engine rooms and boiler rooms was through watertight doors, which could all be closed instantly from the captain's bridge: a single switch, controlling powerful electro-magnets, operated them. They could also be closed by hand with a lever, and in case the floor below them was flooded by accident, a float underneath the flooring shut them automatically.
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