This section is from the book "The Boy Mechanic Vol. 1", by Popular Mechanics Co.. Also available from Amazon: 700 Things for Boys to Do.
By using the circuit shown in the sketch for short-distance telegraph lines, the extra switches and wiring found in many circuits are done away with. Closing either key will operate both sounders, and, as the resistance of the sounders is very high, the batteries do not run down for a long time. --Contributed by A. D. Stoddard, Clay Center, Kan.

Illustration: Simple Telegraph Line
 
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