hammer is here the transmitter, the air the conductor, the ear the receiver.
In wireless telegraphy we use the ether as the conductor of electrical disturbances.13 Marconi, Slaby, Branly, Lodge, De Forest, Popoff, and others have invented apparatus for causing disturbances of the requisite kind, and for detecting their presence.
The main features of a wireless telegraphy outfit are shown in Figs. 59 and 61.
THE TRANSMITTER APPARATUS.
We will first consider the transmitting outfit (Fig. 59). It includes a battery, dispatching key, and an induction coil having its secondary circuit terminals connected with two wires, the one leading to an earth-plate, the other carried aloft on poles or suspended from a kite. In the large station at Poldhu, Cornwall, for transatlantic signalling, there are special wooden towers 215 feet high, between which the aërial wires hang. At their upper and lower ends respectively the earth and aërial wires