Page:The New International Encyclopædia 1st ed. v. 20.djvu/682

* WIRELESS TELEGBAPHY. 584 WIRELESS TELEGRAPHY. through the primary circuit when the key is de- pressed and the interrupter rapidly makes and breaks the circuit which sets up alternating cur- rents in the secondary circuit. It was found that alternating currents propagated the electric im- pulses to a greater distance than direct currents. The receiving end is similar to that in Fig. 1. 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. ^Yhen the key is depressed a direct current will flow 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 hav- 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 the 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 on several factors, including the num- FlG, 4. INDUCTION METHOD. B B VWWM ^ll Fio. 7 10 5. ELECTIIO-STATIC METHOD. ber of turns of wire on the coils, on the size of the latter and their distance apart, etc. Electko-Static Method. In the electro-static method of signaling through space the iiriiiiaiy winding, 1, 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 comieeted to the elevated con- denser or capacity area, 6, and the earthed plate, 7 ; the receiver comprises an electrostatic telephone receiver, 1), made of two thin diapliragnis 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, 8 and 10, respectively. The theory of the action taking place when the instruments are operative is that the earth is cliarged at the sending station to a certain posi- tive potential and the receiving apparatus to an equal negative potential, producing a difference of potential bcMveen the two stations when a cur- rent will How from one to the other, the receiver or indicating device responding to the surging current as the difference of potential is equalized. Electric W.we Method. The last and most practical method employs electric waves. The apparatus for the emission and reception of elec- tric waves in its simplest form consists of a sending instrument similar to the one just de- scribed in the electro-static method, but having the additional factor of the disruptive discharge included in the transmitter, together with a coherer in the receiver. These devices are illustrated in Fig. 6, and all workable wireless telegraph apparatus are con- structed upon fundamental principles involved in the electric wave method and are modifications of that shown in the diagram. The sending apparatus. A, consists of an induc- tion coil, (/, the primary winding of the coil, l. Qo] B -(=rf=h nf-o- 13 14 9 "II Fig. 6. ELECTIIIC WAVE METHOD. being included in a circuit with a battei'y, 2, an interrupter, 3. and a Morse key, 4: a condenser, 5, is shunted around the interrupter, 3. The ter- minals of the secondary coil, 6, lead to the spark- gap, 7, one side of which leads to the aerial wire, 8, and the opposite side to the earth at 9. The receiving device. B, consists of similarly elevated and earthed wires. 10 and 11, connected to a wave-detector. 12. usually of tlic coherer type. The local battery circuit includes the coherer. 12, a battery. 13. ami a telephone receiver, 14. When in action the function of the transmitter is to radiate electromagnetic waves (see Electricity; Wave.s) ; this is accomplished by a series of transformations of the primary electric current generated by tile liattery. This low-voltage di- rect current is rendered intermittent by the in- terrupter, 3. and for every iininilsc through the primary winding of the induetiuu coil an alter-
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