Page:The New International Encyclopædia 1st ed. v. 20.djvu/688

* WIRELESS TELEGRAPHY. 588 WIRELESS TELEGRAPHY. emitted wave the earth would then become a nodal point, and this being the ease it must neces- sarily follow that a second wire of the same length represented by 2, 3, 4, 5, A, in the diagram will, if a current is set up in it, likewise oscil- late in the antenna, 1, 6: with the wave crests at the spark-gap, 2, and the free end of the aerial wire. 1. while the wave valley will be at 6, as graphically shown by the dotted lines. In the resonator,' B, the oscillations set up in the antenna are communicated to the liorizontal auxiliary wire, having a coherer placed at a point where the amplitude of the wave is great- est, as indicated ly the dotted lines. In ac- cordance with these principles all wave lengths different from those predetermined, and to which the instruments are tuned, will dissipate their energy into the earth, since the earth at 6 no longer becomes the node of the waves. JIarconi Syntonic System. In combining open and closed circuits Guglielmo Marconi of Italy has employed radically diflferent methods from those adopted in the preceding systems. This system is, however, largely based on the prin- ciples of the syntonic jars, and may be said to be an extension of this experimental apparatus. In the diagram Fig. 10, the general arrange- ment of the radiator and resonator is shown. Re- FUJ. 16. DIAGRAM OP MARCONI BV8TEM. ferring to the sending apparatus, 1 A represents an inner metal cylinder connected to the earth at 5 ; the outer cylinder, 2, is connected to one side of the spark-gap, 3, the opposite side lead- ing to the inner cylinder and the earth at 5 tlirough the inductance. 4. When the spark takes place the current oscil- lates between the cylinders, emitting a long train of waves haying a low dampiaig factor. The resonator system of the receiver B is similar to the oscillator; the inner cylinder is connected to the earth, while the outer cylinder is connected to earth through the primary of the transformer coil, r, and the inductance, 4': the secondary of the transformer, 2', is connected with the coherer, 3'. The object of placing the latter in a separate circuit is that the free period of oscillation may not be aflfeeted by the high resistance of the coherer. When oscillations are set up in A, waves of a given length are emitted, and Uiosc impinging on B set up currents of a similar fre- (|uency, the cumulative action of which breaks down the resistance of the coherer and registers a dot or a dash as the case may be. In this system a .sensitive relay is connected in series with the coherer; the relay on being actuated closes a second local circuit which in- cludes a Morse printing register and the tajiper used for decohering the filings of the coherer. Fig. 1 on Plate IT. shows the apparatus as ar- runged in a istation. Fig. 17. diagram op BRArir SYSTEM. Bbaun's Resonance System. Another sys- tem employing resonance to effect syntonization is due to Professor Ferdinand Braun of Ger- many. The oscillator and resonator consist of distinct open and closed circuits, as shown in the diagram Fig. 17. In the oscillator, A, the high frequency currents surge through the closed cir- cuit formed by the spark-gap, s, the con- densers, C, C, and the C= primary of the trans- j| former coil, L, where ' they are impressed upon C = the secondary of the transformer, il, in the open circuit oscillator; this oscillivtor radiates waves as rapidly as the , energy is supplied to it, yet of a definite wave length ; the aerial wire, a, should be one-fourth of the wave length ; the opposite terminal, b, is. not grounded, but to maintain the relations be- tween the coefficients the wire h is made equal to a. The receiver, B, comprises the aerial wire, «', and its complementary wire, b'. separated by the condensers, C, C. This is a compound-circuit res- onator. The closed-circuit resonator is joined through c, c and the primary of a transformer, L; oscillations set up by the waves in this circuit are transformed into an open-circuit resonator through the secondary coil by the transformer,, M ; its terminals connect with two wires, d, e, each of which is one-fourth of the wave length, and equal in length to the aerial wire; the coherer is included in the circuit of the wire e, where the amplitude of the wave is greatest. An ordinary coherer of steel filings is employed in a tube which is not exhausted of its air; the tapper is operated by clockwork actuated by the relay and the message is received by a Morse printing register. Fes.sexden Tuned System. This system of syntonic wireless telegraphy is the invention of Professor R. A. Fessenden, and embodies many original features. The diagram Fig. 18 illus- trates a combined sending and receiving sys- tem. The transmitter comprises the aerial wire, 1, the induction coil, 2, spark-gap, 3, and a key, 4, for throwing the aerial wire in and out of tune; the ttining of the oscillator and resonator is aecom|)lished by a variable inductance and capacity made of a number of parallel wires or grid immersed in oil and controlled by movable contacts, 5; this eliminates condensers and coils for obtaining given values of capacity and inductance, and preserves the proper relations between these co- cincicnts. The resonator of the receiver com- prises a similar grid. 0, used for tuning an electric wave detector, actuating the tele- ))hone receiver; the Morse coile is employed, the messages being read from the clicks in the telephone receiver. The electric wave detector is novel in the art of wireless telegrajihy; it con- sists (if a sliint loop of silver wiri'. 13, Fig. 10, having a platinum core; this wire is drawn down to .002 inch: the loop is then fastened to the Icadiiig-in wires, 14; tlic tip of the silver loop i»