Part 8 (1/2)

It has been found possible to send several le line To effect this a _distributer_ is used to put a number of transmitters at one end of the line in communication with an equal number of receivers at the other end, fed by a second distributer keeping perfect ti as a whole to any one instrument it arrives in little bits, but these follow one another so closely as to be practically continuous By working a nuh a distributer, a thousand words or le wire

The Pollak Virag system employs a punched ribbon, and the receiver traces out thestrip of sensitized photographic paper A ht from a lamp on to the strip, which is automatically developed and fixed in che the enious Messages have been transmitted by this system at the rate of 180,000 words per hour

Chapter VII

WIRELESS TELEGRAPHY

The trans apparatus--Syntonic transraphy

In our last chapter we reviewed briefly soes froh a circuit consisting partly of an insulated wire and partly of the earth itself Thecircuit, especially if it be a submarine cable, is costly to install, so that in quite the early days of telegraphy efforts were made to use the ether in the place of wire as one conductor

When a hammer strikes an anvil the air around is violently disturbed

This disturbance spreads through the molecules of the air in much the same way as ripples spread from the splash of a stone thrown into a pond When the sound waves reach the ear they agitate the tympanum, or drum membrane, and we ”hear a noise” The hammer is here the transmitter, the air the conductor, the ear the receiver

In wireless telegraphy we use the ether as the conductor of electrical disturbances[13] Marconi, Slaby, Branly, Lodge, De Forest, Popoff, and others have invented apparatus for causing disturbances of the requisite kind, and for detecting their presence

The s 59 and 61

THE TRANSMITTER APPARATUS

We will first consider the trans key, and an induction coil having its secondary circuit ter to an earth-plate, the other carried aloft on poles or suspended froe station at Poldhu, Cornwall, for transatlantic signalling, there are special wooden towers 215 feet high, bethich the aerial wires hang At their upper and lower ends respectively the earth and aerial wires terap When the operator depresses the key the induction coil charges these balls and the wires attached thereto with high-tension electricity As soon as the quantity collected exceeds the resistance of the air-gap, a discharge takes place between the balls, and the ether round the aerial wire is violently disturbed, and waves of electrical energy are propagated through it The rapidity hich the discharges follow one another, and their travelling power, depends on the strength of the induction coil, the length of the air-gap, and the capacity of the wires[14]

[Illustration: FIG 59--Sketch of the transraphy outfit]

[Illustration: FIG 60--A Marconi coherer]

RECEIVING APPARATUS

The human body is quite insensitive to these etheric waves We cannot feel, hear, or see the station there is what may be called an ”electric eye” Technically it is na 60 Inside a ss, P P, carrying terlass at both ends A sap is partly filled with nickel-silver powder If the terminals of the coherer are attached to those of a battery, practically no current will pass under ordinary conditions, as the particles of nickel-silver touch each other very lightly and make a ”bad contact”

But if the coherer is also attached to wires leading into the earth and air, and ether waves strike those wires, at every iether--and allow battery current to pass The property of cohesion of small conductive bodies when influenced by Hertzian waves was first noticed in 1874 by Professor DE

Hughes while experi with a telephone

[Illustration: FIG 61--Sketch of the receiving apparatus in a wireless telegraphy outfit]