required at a wireless sending station in order to operate a very sensitive receiver many miles away.
If we consider that the light chip resting upon the surface of the water has practically no inertia, it will respond to almost any wave length, and, therefore, if the water were disturbed from some other source than the stone referred to, and while signals were being sent by means of the stone, confusion would result, as the chip would respond to the waves from both sources, and, for this reason, no accurate signals could be made out by watching the motions of the chip. However, this difficulty may be overcome by employing a transmitting device which will send out waves of a certain length, and a receiving apparatus which shall respond only to the wave length of the transmitter.
4. Synchronous Wave Motion and Tuning
If a weight suspended by a spiral spring, or a rubber band, be given a blow so as to cause it to move up and down, the weight will oscillate uniformly; that is, a definite number of times per minute, the frequency depending upon the elasticity of the spring, or rubber band, and the weight of the suspended mass. Now assume this device placed over the pond of still water, as depicted at the left in Fig. 2, and set in motion as described above. On each downward movement of the weight it will touch and disturb the water, and, since
