Wireless Telegraphy and Telephony

WIRELESS TELEGRAPHY 71 chain as shown in the illustration and that it is struck at regular intervals, once every second, with a ham- mer. Every time that the hammer strikes the ball it will give it an impulse and cause it to swing slightly. If the chain is short, the ball will swing faster, while if it is long it will swing more slowly. We will suppose that the Fig. 86.—Chain and ball arranged to illustrate effect of tuning. ball is struck from such a direction that it starts to swing over toward A. The ball is so heavy and the hammer so light in comparison however that the ball does not swing very far and soon commences a return journey. If it should return to the point B just as the hammer delivers another blow the force of the blow will be expended in stopping the ball rather than adding to its motion because they are both traveling in opposite directions. However if the chain is lengthened so that it has a period of swing lasting one second, the succeeding blow will strike the ball after it has reached the point C and is on its return jour- ney, thus imparting fresh energy because both the ball and hammer come together at the right time when they are both swinging together. Proper adjustment of the length of the chain will make it possible for the hammer to always