Wireless Telegraphy and Telephony

io8 WIRELESS TELEGRAPHY each note of each particular instrument. If the fluctuations in pressure of a sound wave are irregular and non-periodic, the sound is called a noise; if they are cyclic, and follow a regular and sufficiently rapid periodic lag, the sound is musical. We may easily satisfy ourselves that in every instance in which the sensation of sound is produced the body from FORK Fig. 123. Experiment showing sounding bodies are in vibration. whence the sound comes must have been thrown into a state of rapid tremor, implying the existence of a motion to and fro of the particles of which it consists. If the face of a tuning fork prong be touched with a small ball of cork suspended from a fine silk fiber, after the fork has been struck and caused to emit its note, the cork will be violently repelled from the latter. Why? Be- cause the prong of the fork is in vibration. If a small wire or bristle is fastened to the prong of the fork and a piece of smoked glass drawn across it while the fork is giving forth a sound, the trace of the point will appear as a wavy line, showing that while the glass was drawn along the prong went to and fro many times.