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Pacinotti, of Florence, constructed a magneto-electric machine in which the current flows always in one direction without a commutator. It has what is known as a ring armature, and is the mother of all dynamos built upon that principle. It is exceedingly ingenious in construction, and for certain purposes in the arts is extensively used.
He suggested the cutting out of the mica pieces almost to the bottom, leaving the commutator bars separated by air-spaces. This scheme was objected to on the ground that particles of graphite would fill these air-spaces and cause a short-circuit.
He caused the current, after it had been rectified by the commutator, to return again into coils of wire round the legs of his field magnets, as shown in the diagram. This induced in them a new supply of magnetism, and this of course intensified the current from the armature.
The port foremost motor was sparking like the devil, rings of cursed sparks shooting round the commutator, but this was no time for ceremony. I relentlessly ordered the field current to be still further reduced.
The commutator, e, is arranged to prevent sparking when the brushes leave a contact piece. This is done by splitting up the brushes into several parts and inserting resistances between the part which leaves the contact piece last and the rest of the circuit. This resistance checks the current ere the final rupture of contact takes place. Figs. 6 and 7 will explain the structure of the commutator.
The pile was covered with a copper jacket whose upper parts supported two Swan lamps. Upon putting on the cover a contact was formed with the electrodes, and it was possible by means of a commutator key with three eccentrics to light or extinguish one of the lamps or both at once. A single element would have sufficed to keep one Swan lamp of feeble resistance lighted for 20 hours.
These wires are connected with the brushes of a commutator, K, on the engine-shaft, which commutator is in electrical connection with the poles of a battery, dynamo-electric machine, or other source of electricity. Instead of two wires to produce a spark, a single wire may be arranged to become incandescent at the proper time for ignition.
It was all very well being able to tell a spark-plug from a commutator at sight, but when it came to a contest in an affair of the heart with a man like Roland, Albert was in his proper place, third at the pole. Probably, if he could have gone on merely being engaged, Roland would never have wearied of the experience.
The reflector is represented by a portion of an ellipse so calculated that one of the foci corresponds to the lamp and the other to the extremity of the instrument. A commutator, B, permits of establishing or interrupting the current at will.
The heat, of whatever origin, is applied from below, and the shaft being revolved, four of the armatures lose their magnetism constantly, while the other four gain it, so to speak. As the moving part revolves, therefore, currents of electricity are set up in the wires of the armatures and are collected by a commutator, as in an ordinary dynamo, placed on the upper end of the central shaft.
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