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Updated: May 17, 2025
Siemens also originated the mechanical idea of hollowing out the legs of the magnet on the inside for the armature to turn in close to the magnet, almost fitting. It was the first time any of these things had been done, and their author probably had no idea that they would be prominent features of the dynamo of a little later time, in all essentials closely imitated.
This was his announcement before a meeting of the Royal Society, held on February 14, 1867, of the discovery of the principle of reinforcing the field magnetism of magneto-electric generators by part or the whole of the current generated in the revolving armature a principle which has been applied in the dynamo-electric machines, now so much used for producing electric light and effecting the transmission of power to a distance by means of the electric current.
These poles are therefore able to attract a separate piece of soft iron or armature A. When the current is stopped, however, the core ceases to be a magnet and the armature drops away.
This neat little instrument is shown in figure 50, where M is the electromagnet, and A is the armature which chatters up and down between two metal stops, as the current is made and broken by the sending-key, and the operator listening to the sounds interprets the message letter by letter and word by word.
This difficulty was solved by dividing the battery at each station into two unequal parts, the smaller battery being always in circuit with the pole-changer ready to have its polarity reversed on the main line to operate the distant polar relay, but the spring retracting the armature of the neutral relay is made so stiff as to resist these weak currents.
At the generating station at Menlo Park four Z dynamos of 110 volts were used, connected two in series, in multiple arc, giving a line voltage of 220. "The motor was located in the front part of the locomotive, on its side, with the armature shaft across the frames, or parallel with the driving axles.
When the machine is first started the current is feeble, because the field of the magnets in which the armature revolves is merely that due to the dregs or "residual magnetism" left in the soft iron cores of the magnet since the last time the machine was used.
But instead of being connected with each other at the posterier end of the armature, as in the Siemens system, they are connected according to chords that correspond to a fourth, a sixth, or any equal fraction whatever of the circumference.
The field coils surround the armature, and there is a laminated iron field structure completing the magnetic circuit. I may say here that surrounding the armature of a dynamo by the field coils, though very recently put forth as a new departure, was described in various Thomson-Houston patents, and to a certain extent all Thomson-Houston machines embody this feature.
My first instrument was made up of an old picture or canvas frame fastened to a table; the wheels of an old wooden clock moved by a weight to carry the paper forward; three wooden drums, upon one of which the paper was wound and passed over the other two; a wooden pendulum, suspended to the top piece of the picture or stretching-frame, and vibrating across the paper as it passes over the centre wooden drum; a pencil at the lower end of the pendulum in contact with the paper; an electro-magnet fastened to a shelf across the picture or stretching frame, opposite to an armature made fast to the pendulum; a type rule and type, for breaking the circuit, resting on an endless band composed of carpet-binding; which passed over two wooden rollers, moved by a wooden crank, and carried forward by points projecting from the bottom of the rule downward into the carpet-binding; a lever, with a small weight on the upper side, and a tooth projecting downward at one end, operated on by the type, and a metallic fork, also projecting downward, over two mercury cups; and a short circuit of wire embracing the helices of the electro-magnet connected with the positive and negative poles of the battery and terminating in the mercury cups."
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