PROGRESS OF "WIRELESS" .367 



lessens the cost of working and provides a more speedy interconnection. It can be com- 

 bined with some manual interconnection in a semiautomatic system. Complete im- 

 proved Strowger automatic systems are at work in Hildesheim, Altenburg, Munich, 

 Graz and Krakow, and a semiautomatic is being prepared for Amsterdam. 



7.. WIRELESS TELEGRAPHY AND TELEPHONY 



In the increasingly important department of wireless telegraphy great progress has 

 been made by G. Marconi in overcoming the difficulties of long distance radioteltgraphy 

 so as to maintain an efficient commercial service. Although some radiotelegraphic work 

 is carried on 1 by means of the Poulsen arc generator, up to the end of 1912 by far the 

 greater part of all the wireless telegraphy in the world was conducted by the spark 

 system, employing intermittent condenser discharges to create long electromagnetic 

 waves. It has been found that for the accomplishment of long distances high antennae 

 or aerial wires are necessary, and in the principal long distance stations the height of the 

 masts or towers which carry these radiating wires is being increased. In Paris the 

 Eiffel Tower is used as a support for antenna wires nearly 1,000 feet in height, and at 

 Poldhu and elsewhere the Marconi Company employ masts 400 feet high. In these 

 wires powerful oscillatory electric currents are set up by the intermittent discharges of 

 large condensers, either air condensers (Marconi) or else glass plate condensers. 



Great improvements have been made in the form of spark gap used. Marconi 

 employs as a spark gap a rapidly revolving disk with studs on it to create several hundred 

 discharges per second in the form of a spark called a musical quenched spark. In 

 Germany a type of discharger due to M. Wien is employed, consisting of flat metal 

 plates in close proximity, which has the property of instantly arresting the electric arc 

 which tends to form between the plates. In the recent forms of spark transmitter pro- 

 ducing a quenched spark, the effect is to impart to the antenna wires a sudden electrical 

 impulse which sets up in them free electrical vibrations. These impulses are repeated 

 several hundred times a second, and result in the radiation from the antenna of corre- 

 sponding groups of electric waves. The signals are made by interrupting these inter- 

 mittent wave trains into long or short groups in accordance with the dash and dot Morse 

 code signals. At the receiving end these waves are picked up or absorbed by a receiving 

 antenna and caused to create similar oscillations in a circuit comprising an adjustable 

 condenser and inductance coil. The signals are mostly read by ear by a telephone 

 receiver, which has placed in series with it a rectifier or valve to convert the rapid 

 electrical oscillations into gushes of electricity in one direction. These gushes coming 

 at the .rate of the spark frequency in the transmitter give rise to a musical note which 

 is interrupted into long and short sound interpretable as Morse code signals. 



Much research has been carried out to discover and explain the action of these oscilla- 

 tion rectifiers. It has been found that certain crystals such as carborundum, an artificial 

 carbide of silicon, conduct electricity better in one direction, and also that a contact 

 between a metal or carbon point and certain metallic sulphides has a similar property. 

 Thus a plumbago point lightly pressed against a surface of galena (lead sulphide) will 

 rectify; also a gold point against a surface of pyrites (iron disulphide). By using a very 

 sensitive galvanometer in series with a crystal of carborundum the radiotelegraphic 

 signals can be photographed on paper slip. The action of these rectifying contacts does 

 not appear to be thermoelectric, and the full reason for the asymmetrical conductivity 

 has not yet been found. Prof. G. W. Pierce discovered that a copper point pressed 

 against a surface of molybdenite is a very excellent oscillation rectifier. 



As regards long distance radiotelegraphy Marconi has had in operation for some 

 years stations conducting transatlantic communications, one at Clifden near Galway in 

 Ireland, communicating with one at Glace Bay in Nova Scotia or with one at Cape Cod 



1 Before the Select Committee of the British House of Commons in November 1912 

 evidence was given of further results of work between San Francisco and Honolulu. But 

 here it is only possible to deal with the situation as known up to that time. See also under 

 Part I, Sect, i., "Extension of Telegraphic Communication." 



