A system of electrotherapeutics as taught by the International correspondence schools, Scranton, . through the movable secondary coils, one of which is used forthe cautery and the other for light. This is because the lines ofmagnetic force have to complete their outside paths for a longdistance through air, making the magnetic circuit one of highresistance, and therefore requiring a correspondingly heaviercurrent to produce the same results as an apparatus in whichthe lines of force may travel almost entirely through iron. Atransformer of the latter class is shown in Fig. 6. Here theprima
A system of electrotherapeutics as taught by the International correspondence schools, Scranton, . through the movable secondary coils, one of which is used forthe cautery and the other for light. This is because the lines ofmagnetic force have to complete their outside paths for a longdistance through air, making the magnetic circuit one of highresistance, and therefore requiring a correspondingly heaviercurrent to produce the same results as an apparatus in whichthe lines of force may travel almost entirely through iron. Atransformer of the latter class is shown in Fig. 6. Here theprimary and secondary coils are entirely enclosed in laminatediron. The strength of the cautery current is regulated by meansof the hand-wheel on top that moves a small lever from onebutton to another. Each button means an addition of one-half §17 PHYSICS OF LIGHT AND CAUTERY 19 volt, the maximum current having a voltage of 6 volts. Thetransformer can be attached to any ordinary lamp-socket of a55- or 110-volt circuit, the three binding-posts to the left being. FIG. 6 for that purpose. On the right are binding-posts for thecautery connections. When the direct current has to be transformed, the procedureis not quite so simple, because a motor-generator, or rotary-converter, is required in addition to the transformer. A motor-generator consists, in reality, of an electric motor that isoperated by a direct current. On the motor shaft is also a sup-plementary armature that revolves in the magnetic field of themotor and has an alternating E. M. F. produced in it, suitablefor the operation of the transformer shown in Fig. 6. In Fig. 7is a diagram showing the connections of the motor-generatorwith the lighting circuit, transformer, and cautery. A is thecurrent-tap, inserted in any lamp-socket, from which the con-ductors a, a transmit a 110-volt current to the motor brushes ofthe motor-generator B, setting its armature in rotation. An alter-nating current of 70 volts is then taken from the
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