The art of wireless telegraphy is based upon wave motion, and an analogy is found in the wave motion of water, as the following explanation should make clear. Picture a small pond of still water, with a chip or twig floating upon its surface, mm full view of the observer. Now if a stone be thrown into the water, the sudden impact of the stone would cause ripples, or small waves, to radiate from the point of impact of the stone with the surface of the water, the waves becoming weaker as the circles become larger, i.e., as the distance from the point of impact becomes greater. As the waves arrive at the point where the chip is floating, they will impart motion to the chip; hence the observer will be aware that there has been some disturbance in the water. (See Fig. 1.) After the waves have ceased, the chip will again lie motionless upon the surface of the water. It is obvious that the distance over which the signals
