High Frequency Apparatus Page 121

PHYSICIANS' OFFICE EQUIPMENT 121 the current delivered by this transformer may be varied to an astonishing degree by placing the clips attached to the flexible connecting cords on different turns of the winding. This wide range of adjustment permits the operator to so attune the apparatus that the circuits through the patient's body and the coil may be brought very closely to resonance. Reference to Fig. 4 will disclose the wiring diagram for the complete outfit. The reader will note that the leads from the condenser and the spark gap are attached to two copper tubes placed parallel with the X-Ray transformer and supported in insulating pillars secured to the top of the table. From these tubes heavy flexible cables complete the oscillation circuit through the primaries of coils 6, 7, and 8. The thoughtful reader will, of course, understand that one coil is connected in the circuit at one time; this permits of a concentration of the full output of the exciting apparatus upon the particular coil in use and obviates the necessity of dividing the energy among the several instruments, only one of which is used at one time. Two sparks gaps are specified in the assembly, Fig. 1. The gap "4" is of the conventional stationary variety with nickel steel or silver electrodes, while the gap "3" is of the rotary type with zinc stationary and aluminum rotary electrodes respectively. The rotary gap is used for the X-Ray and D'Arsonval coils, while the stationary gap is best adapted for the Oudin Coil, No. 6. The current delivered by the latter coil must be under perfect control and in certain classes of vacuum tube work it is necessary that a delicate and perfectly steady high frequency spark be employed. The stationary gap suggested will enable the operator to adjust his current with such delicacy that the spark may be brought from a velvety spray a quarter of an inch in length to a hot, 3 in., caterpillar discharge simply through an adjustment of the length of gap, variation of primary