WIRELESS TELEGRAPHY. 589 WIRE ROPE. then dissolved away with nitric acid, leaving the platinum core exposed; the whole is tlien sealed in a glaas bulb, 15, which is finally exhausted. acts as a tapper for restoring the coherer to its iioriiially liigh resistance. 1)15 Forest XonTuxed System. In this sys- tem of wireless telegraphy no attempt has been made to tune the circuits. The transmitter, Fig. 21, employs an ordinary transformer, 3, which Fig. 18. PESSENDEN COMBINED SENDING AND KECEIVINQ APPAHATC8. This detector operates by the current developed by the oscillators, whereas detectors of the co- herer type operate by the potential established. 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 ap- paratus. Popp-Branley Non-Syn- TONic System. In a system devised by Professor Eduard Branley, the original inventor of tlie coherer, and il. 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 in- vented by Branley. This consists of a bronze disk. Fig. 20, with three steel legs fixed on its surface form- ing a tripod at right angles to its plane. The legs are brought to a point and polished, after ■which they are oxi- ■ Battery dized by heating in ' •!■ — ^ — ' an alcohol flame and tempered : this gives them a thin insulating film of oxide, which pre- vents a low-voltage F.O. 20. DIAGEAM^OF^POPP-BRANLT p^,,.^^,,^ f,.„,„ fl„,y. ingthrough thecon- tact, but when a high-frequency oscillation surges through it the film is broken down, the direct current then follows ami indicates the signal. It is a coherer of exceptional sensitiveness and stability. On Plate II. is sho^vn the coherer mounted on the Jlorse register, which also Fig. 19. FESSENDEN ELECTRIC WAVE DE- TECTOR. Fig. 22. DE FOREST WIRE- LESS TELEGRAPHY SYS- TEM RECEIVER. FlO. 21. DE FOBEBT TRANSFORMER TRANSMITTING APPARATUS. steps up an alternating current generated by the dynamo 1 from .500 to 2.5,000 volts, which charges the Leyden jars, 7, 8, to their capacity, when they discharge through the air-gap, G, set- ting up oscillations in the aerial wire, 4, and the earthed wire, 5. The transmitting apparatus is shown on the Plate. The receiver (see diagram Fig. 22) consists of a new type of wave detector, 1', 1", a battery, V, a telephone receiver, 6' ; the receiver is connect- ed in shunt with the coherer through the con- denser, 5'. Resistances, 2' 2" and 3', are in- serted to compensate for the excess of battery current. The wave de- tector operates diamet- rically opposite to that of the coherer ; in that its resistance is in- creased by the cumula- tive action of the oscillations instead of decreased. For this reason it is termed an anti-coherer; in- stead of metallic filings placed between the con- ductor plugs of the coierer tube, an oxide of lead mixed with glycerin is employed. It is show'n on the accompanying Plate. The action is electro- lytic in character, sin«e 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, Senor .lulio Cervera Baveria of Spain, Jlonsieur E. G. Foresio of Bel- gium, and others, but these are merely modi- fications of the fir.st system operated in 1896 by Guglielmo Marconi. BiBi.ioGR.PHT. Consult: Fahie, A History of WireJess Telegraphy (3d ed., London, 1902) ; Hertz. Electric IFares (New York. 1900) ; Righi and Dessau, Die Telegraphic ohne-Draht (Berlin, 1903) ; Turpain. Les applications pratiques des ondes electriqucs (Paris, 1902); Col- lins, Wireless Telegraphy, Its History, Theory, and Practice (New York, 1904). The reader should also consult the files of the leading elec- trical 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
