. American telephone practice . other change in the direction of the 106 AMERICAN TELEPHONE PRACTICE. current, were it not for the fact that the direction of the lines offorce through the coil also changes. The same cycle of events takesplace during the next half-turn, when the coil is in the position fromwhich it started. We thus see that the current generated is an alternating one,changing its direction twice during every revolution. In practice the armature, instead of having a single turn of wire,as in Fig. JJ, has a great number of turns of fine wire wound on acast-iron core of the form s
. American telephone practice . other change in the direction of the 106 AMERICAN TELEPHONE PRACTICE. current, were it not for the fact that the direction of the lines offorce through the coil also changes. The same cycle of events takesplace during the next half-turn, when the coil is in the position fromwhich it started. We thus see that the current generated is an alternating one,changing its direction twice during every revolution. In practice the armature, instead of having a single turn of wire,as in Fig. JJ, has a great number of turns of fine wire wound on acast-iron core of the form shown in Fig. 78. In this figure, Arepresents a shuttle-shaped core of cast iron, on which the coils ofwire, w, are wrapped. One end of the wire forming the coils isfastened to the pin, p, which is fastened to and is in metallic con-nection with the core, A. The other end is fastened to the pin p,which is insulated from the core, but connects with the pin, c, pro-jecting from the end of the armature shaft and is insulated there-. A G A- FIG. 78.—ARMATURE OF MAGNETO GENERATOR. from by the fiber bushing, b. Projections, a a, integral with thecore, are turned down to form bearings for the armature. Apinion, f, is carried on the end of the shaft, in order to transmit tothe armature the motion received from a large driving-gear wheelwith which it meshes. A magneto generator in connection with a call-bell is showndiagrammatically in Fig. 79. To the poles of the permanent mag-nets, TV S, of the generator are attached cast-iron pole-pieces, P P,bored out so as to allow the armature, A, to turn freely betweenthem. The bearings of the armature are usually mounted on brassplates firmly attached to the ends of the pole-pieces, but not shownin this figure. By means of a crank attached to a suitable gearwheel engaging a pinion on the armature shaft, the armature maybe made to turn rapidly. As the currents generated are alternating, a polarized bell or MAGNETO CALLING APPARATUS. 107 ringer i
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