Part 8 (2/2)

We are now in a position to exa 61) First, we notice the aerial and earth wires, to which are attached other wires fronet R and through two choking coils, whose function is to prevent the Hertzian waves entering the battery The relay, when energized, brings contact D against E and closes the circuit of battery B, which is net M as well as the _tapper_, which is practically an electric bell(The tapper circuit is indicated by the dotted lines)

We will suppose the transmitter of a distant station to be at work The electric waves strike the aerial wire of the receiving station, and cause the coherer to cohere and pass current The relay is closed, and both tapper and Morse inker begin to work The tapper keeps striking the coherer and shakes the particles loose after every cohesion If this were not done the current of A would pass continuously after cohesion had once taken place When the key of the transmitter is pressed down, the waves follow one another very quickly, and the acquired conductivity of the coherer is onlythe impression of a dot by the Morse inker, contact is made and broken repeatedly; but as the armature of the inker is heavy and slow to move it does not vibrate in time with the relay and tapper Therefore the Morse instru depressions of the key at the trans station, while the tapper works rapidly in tirah M the ar an inked wheel, rises, and adrawn forward off reel R by the clockwork--or electrically-driven rollers R1 R2

SYNTONIC TRANSMISSION

If a nues sinals would affect all the receivers round, unless so a receiver sensitive only to the waves intended to influence it Also, if distinction were iht go to undesired stations

There are various ways of ”tuning” receivers and transous to that of ht is suspended froiven an upward blow, it bobs up and down a certain number of ti exactly the same duration as the rest The resistance of the air and the internal friction of the spring gradually lessen the aht finally coht scales 30 lbs, and that it naturally bobs twenty tiive it a push every three seconds you can coax it into vigorousthat every push catches it exactly on the rebound The same effect would be produced more slowly if 6 or 9 second intervals were substituted But if you strike it at 4, 5, or 7 second intervals it will gradually cease to oscillate, as the effect of one blow neutralizes that of another The sa-forks of equal pitch are mounted near one another, and one is struck The other soon picks up the note But a fork of unequal pitch would remain dumb

Now, every electrical circuit has a ”natural period of oscillation” in which its electric charge vibrates It is found possible to ”tune,” or ”syntonize,” the aerial rod or wire of a receiving station with a transth, says Professor JA Fle,[15] has a natural time period of electrical oscillation of about one-millionth of a second Therefore if waves strike this wire a million times a second they will reinforce one another and influence the coherer; whereas a less or greater frequency will leave it practically unaffected By adjusting the receiving circuit to the transraphy becomes possible

ADVANCE OF WIRELESS TELEGRAPHY

The history of wireless telegraphy may be summed up as follows:--

1842--Professor Morse sent aeriala battery and trans one bank and ”earthed” in the river at each end On the other bank was a second wire attached to a receiver and similarly earthed Whenever contact was made and broken on the battery side, the receiver on the other was affected Distance about 1 es across the Tay at Glencarse in a somewhat similar way Distance about 1/2 nalled from Lavernock Point, near Cardiff, to Steep Holm, an island in the Bristol Channel Distance about 5-1/2 miles

In all these electrical _induction_ of current was employed

1886--Hertzian waves discovered

1895--Professor A Popoff sent Hertzian wave nalled froe; 17-1/2 es sent at sea for 380 es transmitted from Poldhu, Cornwall, to Hospital Point, Newfoundland; 2,099devices that his transatlantic es do not affect receivers placed on board shi+ps crossing the ocean, unless they are purposely tuned Atlantic liners now publish daily sh space from land stations In the United States the De Forest and Fessenden syste rapidly extended to embrace the most out-of-the-way districts Every navy of iraphy, which, as was proved during the Russo-japanese War, can be of the greatest help in directing operations

[13] Named after their first discoverer, Dr Hertz of Carlsruhe, ”Hertzian waves”

[14] For long-distance transmission powerful dynamos take the place of the induction coil and battery

[15] ”Technics,” vol ii p 566

Chapter VIII

THE TELEPHONE

The Bell telephone--The Edison transement of a telephone circuit--Double-line circuits--Telephone exchanges--Submarine telephony

For the purposes of everyday life the telephone is even raph Telephones now connect one roo with another, house with house, toith town, country with country An infinitely greater number of words pass over the telephonic circuits of the world in a year than are transraph operators The telephone has become an important adjunct to the transaction of business of all sorts Its wires penetrate everywhere Withoutfrom his desk, the London citizen may hold easy converse with a Parisian, a New Yorker with a dweller in Chicago