. Practical radiography : a handbook for physicians, surgeons, and other users of X-rays . odifications of the original current curve ;we will first describe the more usual type which belongs tothe class of platinum interrupters (Fig. 41). An electro-magnet through which the alternating currentis flowing is mounted opposite one pole of a vibrating bar-magnet, causing the latter to be attracted as often as thepolarity of the electro-magnet is opposite to that of the Induction Coils and Interrupters 85 bar-magnet; that is to say, the bar-magnet will swing insynchronism with either the positive o
. Practical radiography : a handbook for physicians, surgeons, and other users of X-rays . odifications of the original current curve ;we will first describe the more usual type which belongs tothe class of platinum interrupters (Fig. 41). An electro-magnet through which the alternating currentis flowing is mounted opposite one pole of a vibrating bar-magnet, causing the latter to be attracted as often as thepolarity of the electro-magnet is opposite to that of the Induction Coils and Interrupters 85 bar-magnet; that is to say, the bar-magnet will swing insynchronism with either the positive or the negative phasesof the alternating current; a tension spring which permitsof adjustment usually keeps the bar away from the electro-magnet. The bar and the upright supporting it carry theplatinum studs, between which the interruptions of theprimary circuit take place, and the action may be summedup as follows :—Suppose the positive phase of the currentproduces a north pole in the electro-magnet opposite thenorth pole of the bar-magnet; then the latter, both by o o o o ,H P K K P. Fig. 42. magnetic repulsion and by the tension of the adjustingspring, is pressed back against the contact screw, andthe positive phase of the current passes through thecoil, without, however, acting inductively. When, on theother hand, the negative phase is traversing the electro-magnet, there will be the opposite polarity—and conse-quently attraction between bar and electro-magnet—withthe result that the former swings forward and in so doingbreaks contact. In this way the negative phase will actinductively in the coil. To ensure the highest possibleinductive effect, the contact screw and the tension screwmust be so adjusted that the attraction and consequentbreak takes place when the negative phase is exactly at 86 Practical Radiography- its maximum. When the adjustment has been correctlycarried out, the secondary of the coil will yield currentswhich are as nearly uni-directional as those
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