FIG. 12. LODGE'S SYNTONIC JARS. circuit oscillator-the oscillations are very persistent, that is, it requires a much longer time for their conversion into electric waves than in the open-circuit type, but the emitted waves are much more feeble than where the oscillations are damped out rapidly. The receiving jar 1 B is connected through a spark-gap, 2, and a closed circuit, 3, 3, the induction of which is made variable by the sliding metal bar 4. When the feeble electric waves impinge upon the circuit they are transformed into electric oscillations, and by their cumulative effect the jar is charged to its sparking capacity when it breaks down the gap, thus indicating the presence of the waves. This action takes place if the jars, A, B, are in tune, i.e. if their inductance capacity and resistance are identical; but if B is not in tune or syntonized to A it will not respond. Syntonic or selective wireless telegraphy is based on these factors, but inasmuch as the open-circuit oscillations are damped out too quickly to obtain good resonance effects and the closed circuit oscillators are too feeble to cover long distances, these inherent difficulties have not been overcome with any degree of success in a practical way.

PRACTICAL CONSIDERATIONS. In ordinary wireless telegraph practice the first requisite is a powerful wave radiator and the second is a sensi

LODGE-MUIRHEAD TUNED SYSTEM. The first system of wireless telegraphy based on electric resonance was devised by Sir Oliver Lodge of England, and the oscillator and resonator are illustrated diagrammatically in Fig. 13. Recent improvements, to be described, have been added to the original Lodge system both by Dr. Lodge and Dr. Alexander Muirhead; the complete apparatus is shown in the accompanying plate.

Referring to the diagram, A and B represent the sending and receiving circuits respectively; 1, 2, and 1', 2', are capacity areas made of sheet metal in the form of cones; 1 and 2 are connected to the induction coil through the inductances, 5, 5, and the condensers, 4, 4; hese are provided for the purpose of increasing the capacity of the oscillator and for prolonging the oscillations in the circuit and to establish a definite frequency of oscillation and the generation of long electric waves. The capacity areas l' and 2', B, are similar to those of A; they are connected to the primary of a transformer coil, 6; the secondary coil, 7, of the transformer is connected with the coherer, 8; the local battery circuits and indicating appliances are not shown in the diagram, but are clearly shown on the accompanying plate. The coherer of which Fig. 14 is a diagrammatic view is of new type. It consists of a small steel disk a, rotating on a column of mercury, b, contained in the cup d; connection is made through the binding screw h and the platinum wire c; a copper brush, k, bearing on the shaft forms connection with the disk, a, thus completing the circuit. No relay is employed, but the coherer is connected direct to a siphon recorder.

d

h

LODGE

FIG. 14. COHERER.

The capacity areas and instruments are insulated from the earth by the supports 9, 9, A. B. In this system there are no earthed terminals; the object in eliminating the earth as a factor is that it represents a variable capacity, and by loading it on the oscillator and resonator tuning becomes exceedingly difficult.

SLABY-ARCO MULTIPLE SYSTEM. That the earth which seems so necessary to the successful transmission of electric waves over long distances could be employed, Dr. Adolph Slaby and

+6

FIG. 13. DIAGRAM OF LODGE TUNED SYSTEM.
A, transmitter; B, receiver.

tive wave detector. For this reason high aerial wires are employed, and both oscillator and resonator are of the open-circuit type. Excellent results are assured without regard to the coefficients of the circuits, for in this type of apparatus the periodicity of the oscillations and the length of the emitted wave may vary considerably without any untoward results.

The apparatus shown in Fig. 6 was the first form of wireless telegraph employed by Marconi, and has been found to be the most practical to the present time. All the succeeding systems, whether syntonic or non-syntonic, are modifica tions of this type.

emitted wave the earth would then become a nodal point, and this being the case it must necessarily 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 oscillate 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 horizontal auxiliary wire, having a coherer placed at a point where the amplitude of the wave is greatest, as indicated by the dotted lines. In accordance 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.

MARCONI SYNTONIC SYSTEM. In combining open and closed circuits William Marconi of Italy has employed radically different methods from those adopted in the preceding systems. This system is, however, largely based on the principles of the syntonic jars, and may be said to be an extension of this experimental apparatus. In the diagram Fig. 16, the general arrangement of the radiator and resonator is shown. Re

FIG. 16.

DIAGRAM OF MARCONI SYSTEM.

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 leading to the inner cylinder and the earth at 5 through the inductance, 4.

When the spark takes place the current oscillates between the cylinders, emitting a long train of waves having a low damping 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, l', 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 so that the free period of oscillation may not be affected by the high resistance of the coherer. When oscillations are set up in A, waves of a given length are emitted, and these impinging on B set up currents of a similar frequency, 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 includes a Morse printing register and the tapper used for decohering the filings of the coherer. Fig. 1 on plate II. shows the apparatus as arranged in a station.

A

M

M

B

BRAUN'S RESONANCE SYSTEM. Another system employing resonance to effect syntonization is due to Professor Ferdinand Braun of Germany. 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 circuit formed by the spark-gap, s, the condensers, C, C, and the c primary of the transformer coil, L, where' they are impressed upon the secondary of the transformer, M, in the open circuit oscillator; this oscillator 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 between the coefficients the wire b is made equal to a.

b

e

FIG. 17. DIAGRAM OF BRAUN SYSTEM.

The receiver, B, comprises the aerial wire, a', and its complementary wire, b', separated by the condensers, C, C. This is a compound-circuit resonator. 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.

FESSENDEN 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 illustrates a combined sending and receiving system. 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 tuning of the oscillator and resonator is accomplished 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 coefficients. The resonator of the receiver comprises a similar gril, 9, used for tuning an electric wave detector, actuating the telephone receiver; the Morse code is employed, the messages being read from the clicks in the telephone receiver. The electric wave detector is novel in the art of wireless telegraphy; it consists of a short loop of silver wire, 13, Fig. 19, having a platinum core; this wire is drawn down to .002 inch; the loop is then fastened to the leading-in wires, 14; the tip of the silver loop is

FIG. 18. FESSENDEN COMBINED SENDING AND RECEIVING APPARATUS.

This detector operates by the current developed by the oscillators, whereas detectors of the coherer type operate by the potential established.

15

14

13

16

FIG. 19. FESSENDEN ELECTRIC WAVE DETECTOR.

The current wave detector is very rapid in action, and utilizes all the energy of the impressed oscillators. Fig. 3 on Plate I. is a photographic view of the Fessenden apparatus.

POPP - BRANLY NON SYNTONIC SYSTEM. In a system devised by Professor Edouard Branly, the original inventor of the coherer, and M. Victor Popp of France, the general arrangement shown in Fig. 20 is employed. The chief feature of this system lies in a new type of coherer invented by Branly. This consists of a bronze disk, D, Fig. 20, with three steel legs fixed on its surface forming a tripod at right angles to its plane. The legs are brought to a point and polished, after which they are oxidized by heating in alcohol flame and tempered; this gives them a thin insulating film of oxide, which prevents a low-voltage FIG. 20. DIAGRAM OF POPP-BRANLY current from flowing through the contact, but when a high-frequency oscillation surges through it the film is broken down, the direct current then follows and indicates the signal. It is a coherer of exceptional sensitiveness and stability. On Plate II. is shown the coherer mounted on the Morse register, which also

Battery

SYSTEM.

an

A

5

FIG. 21. DE FOREST TRANSFORMER TRANSMITTING
APPARATUS.

steps up an alternating current generated by the dynamo 1 from 500 to 25,000 volts, which charges the Leyden jars, 7, 8, to their capacity, when they discharge through the air-gap, 6, setting up oscillations in the aerial wire, 4, and the earthed wire, 5. The transmitting apparatus is shown on the plate.

9

B 9

FIG. 22. DE FOREST WIRELESS TELEGRAPHY SYSTEM RECEIVER.

The receiver (see diagram Fig. 22) consists of a new type of wave detector, 1', 1", a battery, 4', a telephone receiver, 6'; the receiver is connected in shunt with the coherer through the condenser, 5'. Resistances, 2' 2" and 3', are inserted to compensate for the excess of battery current. The wave detector operates diametrically opposite to that of the coherer; in that its resistance is increased by the cumulative action of the oscillations instead of decreased. For this reason it is termed an anti-coherer; instead of metallic filings placed between the conductor plugs of the coherer tube, an oxide of lead mixed with glycerin is employed. It is shown on the accompanying plate. The action is electrolytic in character, since the direct current from the battery builds up connecting threads and these are disrupted when the oscillations take place. Systems have been devised by Monsieur E. Ducretet of France, Señor Julio Cervera Baveria of Spain, Monsieur Emil Guarin Foresio of Belgium, and others, but these are merely modifications of the first system operated in 1896 by William Marconi.

BIBLIOGRAPHY. Consult: Fahie, A History of Wireless Telegraphy (3d ed., London, 1902); Hertz, Electric Waves (New York, 1900); Righi and Dessau, Die Telegraphie ohne Draht (Berlin 1903); Turpain, Les applications practique des ondes electriques (Paris, 1902); Collins, Wireless Telegraphy, Its History, Theory, and Practice (New York, 1904). The reader should also consult the files of the leading electrical journals both American and European, where he will find detailed descriptions of the various systems and the improvements made in them from time to time.

WIRE ROPE. Rope composed of twisted strands each composed of metal wires twisted together. Wire ropes are now used generally