Wireless Telegraphy and Telephony

WIRELESS TELEGRAPHY 61 produce a sound themselves. They are the wires to which the impulses are rightly tuned so that each one adds to the motion it has already acquired. We all know how a child sitting in a swing may be made to swing back and forth by giving a succession of little impulses properly timed. The small pushes are superimposed on one another, the result being a single large motion. Fig. 76.—Analogy between swinging and tuning. The “impulses” generated in the receiving aerial are exceedingly weak and in order to produce an effect must be timed so as to follow one another in proper succession. Tuning devices are for this purpose and by their means the receiving circuits and instruments may be carefully ad- justed to the same wave length or “note” as the transmitter so that the high frequency currents in the aerial will arrive at the proper time to oscillate or surge back and forth to produce the maximum results. In this way it is possible to convey intelligence over long- distances by the repetition of small impulses without it