High Frequency Apparatus Page 122

122 HIGH FREQUENCY APPARATUS turns and changes of the current regulator on the low frequency transformer. The rotary gap is intended for longcontinued treatments where the apparatus is working at aproximately full power during the entire length of time. While the stationary gap is in use, the disc of the rotary is turned so that the electrodes are opposite the open spaces in the periphery of the disc; when the rotary gap is to be used, the adjustable electrode of the stationary gap is merely opened until the spark prefers to pass by means of the rotary. A useful accessory to the apparatus is shown mounted on top of the D'Arsonval coil, 8. This is a hot wire meter that will indicate accurately the amount of current passing through the patient's body while the D'Arsonval treatment is being given. The design for a simple hot wire meter is given in the next chapter for the sake of completeness, but in view of the fact that a standard instrument of the type shown in the illustration can be purchased for $12.00, the amateur builder is scarcely justified in attempting the construction. The low frequency transformer, 2, which converts the residence lighting current into a high potential one suitable for charging the condenser of the outfit, is a standard magnetic leakage instrument with a variation in the number of turns in the primary. The alternating current supply from the house mains is connected with the knife switch shown directly above the transformer and from the switch a cable leads to the low-tension terminals of the transformer. The snap switch controls the rotary spark gap motor. The condenser is the glass plate type arranged in sections or units which may be connected in multiple one section at a time by means of the single pole knife switches shown on the top of the cabinet (5 in Fig. 1).