INDUCTION METHOD. Another method for wire less telegraphy and one that is ideal in its sim plicity is based on induction. Two coils of wire, A. B. Fig. 4. are arranged parallel with each other and at some little dis tance apart. When the key is depressed a direct current will How through the circuit A and a mag netic field of force will be produced around the coil of wire. the curved lines proceeding at right an gles from the coil itself, and these will extend to a considerable distance; some of these magnetic lines will thread through the receiving coil B, and alternating currents hay ing the same frequency phase and amplitude will manifest themselves, but owing to the fact that the magnetic energy decreases as the square of the distance. the poten tial as well as tlm current impressed upon the receiving coil will be very much less in accord ance with the laws of magnetic induction.
In this method of wireless telegraphy the distance to which signals may be transmitted depends ou several factors, including the num winding, I, of the induction coil a is connected in series with a telegraph key, 2, and a battery, 3, as shown in A, Fig. 5; the secondary terminals
of the coils are connected to the elevated con denser or capacity area, 6, and the earthed plate, 7; the receiver comprises an electro-statie telephone receiver. 9, mad' of two thin diaphragms of metal and placed very closely together, form ing an air condenser, these being arranged in a telephone receiver: the two diaphragms are con nected to the capacities area, the earthed plates, S and lO. respectively.
The theory of the action taking place when the instruments are operative is that the earth is charged at the sending station to a certain posi tive potential and the receiving apparatus to an equal negative potential, producing a difference of potential betMveen the two stations when a cur rent will flow from one to the other. the receiver or indicating device responding to the surging current as the ditTerenee of potential is equalized.