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Things to Know and Do 125 sending range and should be used if you can get alternating current to work it with. THE TELEGRAPH KEY. The purpose of the key is to break up the battery or fighting current which energizes the primary coil of the induction coil, or the transformer, into dots and dashes representing the letters of the alphabet, or International Morse Code as it is called. The key is connected in circuit with the primary of the coil and the battery or other source of current. THE BATTERY on POWER CIRCUIT. From either the one or the other the power to operate your induction coil or transformer is L E YDE/V JflR3 7'0 9531141; To GROUND Fig 3. Transmitter ready to send had. If current from a lighting circuit is used a variable resistance must be connected in the primary circuit to cut down the cur- rent to the amount required. THE SPARK-GAP. This is simply a pair of brass rods fitted with