. Elementary and dental radiography . the armature, or revolving conductor, and the rings, or appliancefor carrying off the electricity. If the current sent out is direct insteadof alternating, a commutator instead of rings must be used. A commu-tator is an appliance which changes the alternating current induced inthe armature into a direct current as it leaves the dynamo. The electro-dynamo, an example of which is shown in Fig. 8. dif-fers in principle trc^m the magneto-dynamo o\\\\ in the kind oi magnetsused. Permanent mas^nets are used in the maerneto-dvnamo whereaselectro-magnets are used
. Elementary and dental radiography . the armature, or revolving conductor, and the rings, or appliancefor carrying off the electricity. If the current sent out is direct insteadof alternating, a commutator instead of rings must be used. A commu-tator is an appliance which changes the alternating current induced inthe armature into a direct current as it leaves the dynamo. The electro-dynamo, an example of which is shown in Fig. 8. dif-fers in principle trc^m the magneto-dynamo o\\\\ in the kind oi magnetsused. Permanent mas^nets are used in the maerneto-dvnamo whereaselectro-magnets are used in the electro-dynamo. Immense electro-dynamos, or generatc^rs, as thev are called, make 10 ELEMENTARY RADIOGRAPHY our commercial currents, steam power being used to revolve their arma-tures. By commercial current is meant the electric current supplied tous by the electric light and power companies. Let us trace a current of electricity through what is known as theelectric circuit. When the armature is revolved the potential at C, of. Fig. 9. Six Pole Direct Current Generator, parts disassembled. E, electro-magnets with polesof different denominations directly opposite one another—the field. Large alternating currentgenerators have as many as 40 poles in the field which revolves, the armature remaining stationary. A, armature. C, commutator. Fig. 7, rises. The potential of the positive wire attached to binding post-{-(which post is connected to C) is instantly raised to that of C, andthe current ceases to flow, potential being equalized between the arma-ture and the positive wire. If now the positive wire of the high poten-tial be brought in contact with the negative wire, which is of low poten-tial, the current flows into the latter. The negative wire is attached tothe negative binding post, which is connected to the magnets the current passes through the negative wire into the magnets,which have a low potential. The current will continue to flow, makinga cir
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