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The resulting arc is spread by powerful electro-magnets, so." And he illustrated with his eight acid-stained fingers. "Spread out like a disk or sphere of flame, of electric fire, you see." "Yes, and what then?" demanded Flint, while his partner, forgetting now to smile, sat there by the window scrutinizing him.
In the "magneto-electric" machine the FIELD MAGNETS are simply steel bars permanently magnetised, but in the ordinary dynamo the field magnets are electro-magnets excited to a high pitch by means of the current generated in the moving conductor or armature. In the "series-wound" machine the whole of the current generated in the armature also goes through the coils of the field magnets.
That night and far into the morning Kennedy was working in the laboratory on a peculiarly complicated piece of mechanism consisting of electro-magnets, rolls, and a stylus and numerous other contrivances which did not suggest to my mind anything he had ever used before in our adventures. I killed time as best I could watching him adjust the thing with the most minute care and precision.
The ease with which powerful electro-magnets can be constructed has led many to believe that the power of an electro-motor can be increased almost infinitely, without a corresponding increase of energy spent. The strongest magnet can be produced with an exceedingly small current, if we only wind sufficient wire upon an iron core.
In all the earlier machines permanent magnets of steel were used. The next important step was to use electro-magnets of soft iron, excited by a current flowing through many turns of wire wound around the legs of the magnet. These could be made much more strongly magnetic than the permanent magnets.
The coils, both in the armature and electro-magnets, are packed as closely as they may to each other, and have thus a compressed or quadrilateral shape. The arrangement is shown in Figs. 1 and 2, which represent, in side view and plan, the armature pulley with the soft iron rim and coils attached.
He saw, during the appearance of the aurora borealis of November 17, 1848, the soft iron armatures employed in the electric telegraph between Florence and Pisa remain attached to their electro-magnets, as if the latter were powerfully magnetized, without, however, the apparatus being in action, and without the currents in the battery being set in action.
His researches on the dynamo caused him to devise what he calls an 'harmonic engine. It consists of a tuning-fork, kept in vibration by two small electro-magnets, excited with three or four battery cells. It is capable of working a small pump, but is little more than a scientific curiosity.
He invited all the reporters to Menlo Park, and, after elaborately explaining the merits of a new catarrh remedy, showed some lines on a piece of paper, which, he said, represented huge electro-magnets, which he proposed to set up along the coast, say, near Barnegat. When the enemy's iron ships appeared, he proposed to excite these magnets, and draw the vessels on the rocks.
We could get even more than 7 horse power out of this machine, by either running it at an excessive speed, or by using excessive currents; in both cases, however, we should shorten the life of the apparatus. An electro-motor consists, generally, of two or more electro-magnets so arranged that they continually attract each other, and thereby convey power.
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