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Those who have facilities for carrying out experiments may prove it in the following manner: E, in the inclosed drawing, is an electro-magnet whose brushes press on two metallic bands, B and B, fixed to but insulated from the spindle, A. The band, B, is in electrical circuit with the shunt commutator, S, and the main commutator, M; while the band, B, is in contact with shunt commutator, S, and main commutator, M. This contact is made by conducting rods, as indicated.
But the action of the spirals can be annulled without sensibly diminishing the magnetism of the core by arranging a second system of spirals identical with the first, but placed in a plane at right angles therewith, or, more simply still, by having a single system of spirals comprising the coil of the electro-magnet, but distributed in a plane that is oblique with respect to the needle's position of rest.
At each selenium contact of the rectangular disk there is a corresponding contact to the battery and electro-magnet.
In fact, the deportment of the wire resembles far more that of a body moving in a resisting medium than anything else; the resistance ceasing when the motion is suspended. Let us imagine the case of a liquid so mobile that the hand may be passed through it to and fro, without encountering any sensible resistance. It resembles the motion of a conductor in the unexcited field of an electro-magnet.
"While, therefore, I claim to be the first to propose the use of the electro-magnet for telegraphic purposes, and the first to construct a telegraph on the basis of the electro-magnet, yet to Professor Henry is unquestionably due the honor of the discovery of a fact in science which proves the practicability of exciting magnetism through a long coil or at a distance, either to deflect a needle or to magnetize soft iron."
If the iron is allowed to remain there as a core, the combination of coil and core becomes an electro-magnet, that is to say, a magnet which is only a magnet so long as the current passes. A U-shaped core of soft iron is wound with insulated wire W, and when a current is sent through the wire, the core is found to become magnetic with a "north" pole in one end and a "south" pole in the other.
The arrangement may be called an electric clutch, that may be arranged in many ways, and the detail of its action is unimportant in description, so that it be borne in mind that each time a notch is passed in turning the shaft by drawing upon or relaxing the cords attached to the pencil-point, an impulse of electricity is sent to an electro-magnet and armature which allows a corresponding wheel and its shaft to turn one notch, or as many notches, as are passed at the transmitting shaft.
The remaining defect in the Morse machine, as first seen by me, was that the coil of wire around the poles of the electro-magnet consisted of but a few turns only, while, to give the greatest projectile power, the number of turns should be increased from tens to hundreds, as shown by Professor Henry in his paper published in the 'American Journal of Science, 1831.... After substituting the battery of twenty cups for that of a single cup, we added some hundred or more turns to the coil of wire around the poles of the magnet and sent a message through two hundred feet of conductors, then through one thousand feet, and then through ten miles of wire arranged on reels in my own lecture-room in the New York University in the presence of friends."
But a reference to the sketches made on board the Sully will show that the original system of signs consisted of dots and lines, and that the first conception of the means to produce these signs was by an up-and-down motion of a lever controlled by an electro-magnet.
In 1830 Hubert Recy published an account of a system of Teletatodydaxie, by which the electric spark was to ignite alcohol and indicate the signals of a code. But spark or frictional electric telegraphs were destined to give way to those actuated by the voltaic current, as the chemical mode of signalling was superseded by the electro-magnet.
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