268 WIRELESS TELEGRAPHY. 



arrangement, however, is to secure a radiator having- large capacity 

 for s^'ntonic purposes, to be referred to presently. 



The vertical wire is usually of stranded copper, about one-fourth inch 

 in dianietc]', although Marconi for this purpose uses also strips of wire 

 netting sihout 2 feet broad. On land the wire or netting is supported 

 by masts of proper height, securely guyed. On ships the ordinary 

 masts suffice. It is not necessary that the wire be suspended strictly 

 vertically so long as the desired vertical height is ol)tained. The Avire 

 is thoroughl}" insulated from the mast at the top by sticks of ru])ber or 

 ebonite, and is led in througli an open window or -hatchway to the 

 room where the transmitting and receiving appai'atus are situated. 

 This thorough insulation is necessary, because, although the discharge 

 knobs of the oscillator ai'e separated by an air space of only half an 

 inch or less, the induction coil used in connection with the oscillator 

 is often capable of producing a spark that will jump 10 or 12 inches 

 through air. The actual appearance of the induction coil, discharge 

 knobs, vertical wire, etc., is well illustrated l)y the upper figure on 

 Plate III. The heavy current and high pressures in the circuits of the 

 oscillator have necessitated the employment of a much larger key for 

 manipulating the oscillator circuits than is used in ordinary Morse 

 telegraphy. 



At an early period of the practical history of Hertzian- wave teleg- 

 raphy it was seen that the usefulness of this art might l)e considerably 

 curtailed by the fact that but one message could be transmitted 

 between any two stations within the sphere or "radius" of influence 

 of a transmitter, since tlie attempt to transmit even two messages at 

 one time would result in an unintelligible mixture of both messages. 

 Several inventors have been at work trying to overcome this defect, 

 and, it is claimed, with success, notal)ly Dr. Lodge, Sig. Marconi, and 

 Dr. Slaby, The plan followed })y these gentlemen has l)een that of 

 emplo^'ing a syntonic or tuning method; that is, the transmitting and 

 recei\'ing circuits are adjusted or "attuned"" to a given rate of 

 electrical oscillations. 



It is a well-known experiment that when two' tuning forks having 

 an identical fundamental rate of vibrations are placed in suitable 

 proximity either fork may ])e set into vibration by air waves set up 

 by the other foi'k and neither will be set into vibration by another 

 fork of a difl'erent note. The tuning fork is a persistent vibrator ]>y 

 virtue of two (lualities which it possesses — elasticity and inertia. 

 When struck a smart blow, it moves from its point of rest; directly 

 its elasticity i-eturns it to its point of rest, its inertia carries it past 

 that point, its elasticity returns it to zero point, inertia carries it past, 

 and so on, until the resistance of the air and other causes stop it. 

 Analogously, an electrical circuit may be given, in almost an}' desired 



