var presentation = ["The Romance of Modern Invention\nby Archibald Williams<\/phrase>","WIRELESS TELEGRAPHY<\/word>","WIRELESS TELEGRAPHY<\/strong><\/phrase>","man<\/word>","Tawell<\/word>","Quaker<\/word>","train<\/word>","Slough Station on the Great Western Railway<\/word>","London<\/word>","charge<\/word>","foul murder<\/word>","murder<\/word>","place<\/word>","Paddington<\/word>","detective met<\/word>","convenient opportunity<\/word>","first time<\/word>","good dormant<\/word>","electric telegraph<\/word>","One day in 1845 a man<\/strong> named Tawell<\/strong>, dressed as a Quaker<\/strong>, stepped into\na train<\/strong> at Slough Station on the Great Western Railway<\/strong>, and travelled\nto London<\/strong>. When he arrived in London<\/strong> the innocent-looking Quaker<\/strong> was\narrested, much to his amazement and dismay, on the charge<\/strong> of having\ncommitted a foul murder<\/strong> in the neighbourhood of Slough. The news of\nthe murder<\/strong> and a description of the murderer had been telegraphed from\nthat place<\/strong> to Paddington<\/strong>, where a detective met<\/strong> the train<\/strong> and shadowed\nthe miscreant until a convenient opportunity<\/strong> for arresting him\noccurred. Tawell<\/strong> was tried, condemned, and hung, and the public for\nthe first time<\/strong> generally realised the power for good dormant<\/strong> in the as\nyet little developed electric telegraph<\/strong>.<\/phrase>","mid-Atlantic laden<\/word>","opposite directions<\/word>","Ireland<\/word>","Newfoundland<\/word>","electric message<\/word>","August<\/word>","New World<\/word>","Thirteen years later two vessels met in mid-Atlantic laden<\/strong> with cables\nwhich they joined and paid out in opposite directions<\/strong>, till Ireland<\/strong>\nand Newfoundland<\/strong> were reached. The first electric message<\/strong> passed on\nAugust<\/strong> 7th of that year from the New World<\/strong> to the Old. The telegraph\nhad now become a world-power.<\/phrase>","epoch-making event<\/word>","recent date<\/word>","December<\/word>","Guglielmo Marconi<\/word>","twenty-two years<\/word>","greater fame<\/word>","Hospital Point<\/word>","long wire<\/word>","delicate tube<\/word>","tiny particles<\/word>","telephone ear-piece<\/word>","far-off Cornwall<\/word>","Cornish station<\/word>","short dot signals<\/word>","mysterious ether<\/word>","strange substance<\/word>","The third epoch-making event<\/strong> in its history is of recent date<\/strong>. On\nDecember<\/strong> 12, 1901, Guglielmo Marconi<\/strong>, a young Italian, famous all over\nthe world when but twenty-two years<\/strong> old, suddenly sprang into yet\ngreater fame<\/strong>. At Hospital Point<\/strong>, Newfoundland<\/strong>, he heard by means of a\nkite, a long wire<\/strong>, a delicate tube<\/strong> full of tiny particles<\/strong> of metal,\nand a telephone ear-piece<\/strong>, signals transmitted from far-off Cornwall<\/strong>\nby his colleagues. No wires connected Poldhu, the Cornish station<\/strong>, and\nHospital Point<\/strong>. The three short dot signals<\/strong>, which in the Morse code\nsignify the letter S, had been borne from place<\/strong> to place<\/strong> by the\nlimitless, mysterious ether<\/strong>, that strange substance<\/strong> of which we now\nhear so much, of which wise men declare we know so little.<\/phrase>","great achievement<\/word>","immense importance<\/word>","report<\/word>","Atlantic<\/word>","cable companies<\/word>","use<\/word>","cable shares<\/word>","again<\/word>","time<\/word>","last<\/word>","great triumph<\/word>","Marconi's great achievement<\/strong>, which was of immense importance<\/strong>,\nnaturally astonished the world. Of course, there were not wanting\nthose who discredited the report<\/strong>. Others, on the contrary, were seized\nwith panic and showed their readiness to believe that the Atlantic<\/strong> had\nbeen spanned a\u00ebrially, by selling off their shares in cable companies<\/strong>.\nTo use<\/strong> the language of the money-market, there was a temporary \"slump\"\nin cable shares<\/strong>. The world again<\/strong> woke up--this time<\/strong> to the fact that\nexperiments of which it had heard faintly had at last<\/strong> culminated in a\ngreat triumph<\/strong>, marvellous in itself, and yet probably nothing in\ncomparison with the revolution in the transmission of news that it\nheralded.<\/phrase>","treat<\/word>","single chapter<\/word>","same time<\/word>","pass<\/word>","book<\/word>","object<\/word>","latest developments<\/word>","scientific research<\/word>","leading place<\/word>","reason<\/word>","first pages<\/word>","different systems<\/word>","The subject of Wireless Telegraphy<\/strong> is so wide that to treat<\/strong> it fully\nin the compass of a single chapter<\/strong> is impossible. At the same time<\/strong> it\nwould be equally impossible to pass<\/strong> it over in a book<\/strong> written with the\nobject<\/strong> of presenting to the reader the latest developments<\/strong> of\nscientific research<\/strong>. Indeed, the attention that it has justly\nattracted entitle it, not merely to a place<\/strong>, but to a leading place<\/strong>;\nand for this reason<\/strong> these first pages<\/strong> will be devoted to a short\naccount of the history and theory of Wireless Telegraphy<\/strong>, with some\nmention of the different systems<\/strong> by which signals have been sent\nthrough space.<\/phrase>","point<\/word>","attack<\/word>","great topic<\/word>","ether<\/word>","science<\/word>","more attention<\/word>","many phenomena<\/word>","present<\/word>","uncertain origin<\/word>","On casting about for a point<\/strong> at which to begin, the writer is tempted\nto attack<\/strong> the great topic<\/strong> of the ether<\/strong>, to which experimenters in many\nbranches of science<\/strong> are now devoting more and more attention<\/strong>, hoping\nto find in it an explanation of and connection between many phenomena<\/strong>\nwhich at present<\/strong> are of uncertain origin<\/strong>.<\/phrase>","first place<\/word>","like<\/word>","form<\/word>","correct<\/word>","touch<\/word>","matter<\/word>","What is Ether<\/strong>? In the first place<\/strong>, its very existence is merely\nassumed, like<\/strong> that of the atom and the molecule. Nobody can say that\nhe has actually seen or had any experience of it. The assumption that\nthere is such a thing is justified only in so far as that assumption\nexplains and reconciles phenomena of which we have experience, and\nenables us to form<\/strong> theories which can be scientifically demonstrated\ncorrect<\/strong>. What scientists now say is this: that everything which we\nsee and touch<\/strong>, the air, the infinity of space itself, is permeated by\na _something_, so subtle that, no matter<\/strong> how continuous a thing may\nseem, it is but a concourse of atoms separated by this something, the\nEther<\/strong>. Reasoning drove them to this conclusion.<\/phrase>","bell<\/word>","Pump<\/word>","sound<\/word>","further side<\/word>","light<\/word>","absolute gap<\/word>","outside atmosphere<\/word>","suppose<\/word>","measure<\/word>","heat<\/word>","iron atoms<\/word>","intervening spaces<\/word>","It is obvious that an effect cannot come out of nothing. Put a clock\nunder a bell<\/strong>-glass and you hear the ticking. Pump<\/strong> out the air and the\nticking becomes inaudible. What is now not in the glass that was there\nbefore? The air. Reason<\/strong>, therefore, obliges us to conclude that air is\nthe means whereby the ticking is audible to us. No air, no sound<\/strong>.\nNext, put a lighted candle on the further side<\/strong> of the exhausted\nbell<\/strong>-glass. We can see it clearly enough. The absence of air does not\naffect light<\/strong>. But can we believe that there is an absolute gap<\/strong> between\nus and the light<\/strong>? No! It is far easier to believe that the bell<\/strong>-glass\nis as full as the outside atmosphere<\/strong> of the something that\ncommunicates the sensation of light<\/strong> from the candle to the eye. Again<\/strong>,\nsuppose<\/strong> we measure<\/strong> a bar of iron very carefully while cold and then\nheat<\/strong> it. We shall find that it has expanded a little. The iron atoms<\/strong>,\nwe say, have become more energetic than before, repel each other and\nstand further apart. What then is in the intervening spaces<\/strong>? Not air,\nwhich cannot be forced through iron whether hot or cold. No! the\nether<\/strong>: which passes easily through crevices so small as to bar the way\nto the atoms of air.<\/phrase>","Minneapolis<\/word>","[Illustration: _A Corner of M. Marconi's cabin on board S.S.\n\"Minneapolis<\/strong>,\" showing instruments used in Wireless Telegraphy<\/strong>._]<\/phrase>","end<\/word>","iron bar<\/word>","electric battery<\/word>","other end<\/word>","positive pole<\/word>","current passes<\/word>","ether gaps<\/word>","Once more, suppose<\/strong> that to one end<\/strong> of our iron bar<\/strong> we apply the\nnegative \"pole\" of an electric battery<\/strong>, and to the other end<\/strong> the\npositive pole<\/strong>. We see that a current passes<\/strong> through the bar, whether\nhot or cold, which implies that it jumps across all the ether gaps<\/strong>, or\nrather is conveyed by them from one atom to another.<\/phrase>","medium whereby heat<\/word>","electricity<\/word>","The conclusion then is that ether<\/strong> is not merely omnipresent,\npenetrating all things, but the medium whereby heat<\/strong>, light<\/strong>,\nelectricity<\/strong>, perhaps even thought itself, are transmitted from one\npoint<\/strong> to another.<\/phrase>","imagine<\/word>","ether behaving<\/word>","way void<\/word>","In what manner is the transmission effected? We cannot imagine<\/strong> the\nether behaving<\/strong> in a way void<\/strong> of all system.<\/phrase>","answer<\/word>","wave motion<\/word>","elastic solid<\/word>","call<\/word>","motion adjoining particles<\/word>","resultant movement<\/word>","The answer<\/strong> is, by a wave motion<\/strong>. The ether<\/strong> must be regarded as a very\nelastic solid<\/strong>. The agitation of a portion of it by what we call<\/strong> heat<\/strong>,\nlight<\/strong>, or electricity<\/strong>, sets in motion adjoining particles<\/strong>, until they\nare moving from side to side, but not forwards; the resultant movement<\/strong>\nresembling that of a snake tethered by the tail.<\/phrase>","sensitive instruments<\/word>","depend<\/word>","various waves<\/word>","waves number<\/word>","long<\/word>","double<\/word>","number<\/word>","violet light<\/word>","These ether<\/strong> waves vary immensely in length. Their qualities and\neffects upon our bodies or sensitive instruments<\/strong> depend<\/strong> upon their\nlength. By means of ingenious apparatus the lengths of various waves<\/strong>\nhave been measured. When the waves number<\/strong> 500 billion per second, and\nare but the 40,000th of an inch long<\/strong> they affect our eyes and are\nnamed light<\/strong>--red light<\/strong>. At double<\/strong> the number<\/strong> and half the length, they\ngive us the sensation of violet light<\/strong>.<\/phrase>","number increases<\/word>","blind<\/word>","detect<\/word>","slower vibration<\/word>","red light<\/word>","reach<\/word>","slow pace<\/word>","When the number increases<\/strong> and the waves shorten further, our bodies\nare \"blind<\/strong>\" to them; we have no sense to detect<\/strong> their presence.\nSimilarly, a slower vibration<\/strong> than that of red light<\/strong> is imperceptible\nuntil we reach<\/strong> the comparatively slow pace<\/strong> of 100 vibrations per\nsecond, when we become aware of heat<\/strong>.<\/phrase>","unknown octaves<\/word>","Thus<\/word>","electric waves<\/word>","Professor Clerk Maxwell<\/word>","wave<\/word>","subsequent research<\/word>","electric currents<\/word>","Bonn<\/word>","Ether<\/strong> waves may be compared to the notes on a piano, of which we are\nacquainted with some octaves only. The gaps, the unknown octaves<\/strong>, are\nbeing discovered slowly but surely. Thus<\/strong>, for example, the famous\nX-rays have been assigned to the topmost octave; electric waves<\/strong> to the\nnotes between light<\/strong> and heat<\/strong>. Forty years ago Professor Clerk Maxwell<\/strong>\nsuggested that light<\/strong> and electricity<\/strong> were very closely connected,\nprobably differing only in their wave<\/strong>-length. His theory has been\njustified by subsequent research<\/strong>. The velocity of light<\/strong> (185,000 miles\nper second) and that of electric currents<\/strong> have been proved identical.\nHertz, a professor in the university of Bonn<\/strong>, also showed (1887-1889)\nthat the phenomena of light<\/strong>--reflection, refraction, and concentration\nof rays--can be repeated with electric currents<\/strong>.<\/phrase>","different natures<\/word>","We therefore take the word of scientists that the origin of the\nphenomena called light<\/strong> and electricity<\/strong> is the same--vibration of\nether<\/strong>. It at once occurs to the reader that their behaviour is so\ndifferent that they might as well be considered of altogether\ndifferent natures<\/strong>.<\/phrase>","thinnest sheet<\/word>","convey electricity<\/word>","many corners<\/word>","please<\/word>","whereas light<\/word>","travel<\/word>","straight lines<\/word>","For instance, interpose the very thinnest sheet<\/strong> of metal between a\ncandle and the eye, and the light<\/strong> is cut off. But the sheet will very\nreadily convey electricity<\/strong>. On the contrary, glass, a substance that\nrepels electricity<\/strong>, is transparent, _i.e._ gives passage to light<\/strong>. And\nagain<\/strong>, electricity<\/strong> can be conveyed round as many corners<\/strong> as you\nplease<\/strong>, whereas light<\/strong> will travel<\/strong> in straight lines<\/strong> only.<\/phrase>","clear<\/word>","metal screen<\/word>","thin tank<\/word>","light passes<\/word>","light forces<\/word>","remember<\/word>","open space conveys<\/word>","To clear<\/strong> away our doubts we have only to take the lighted candle and\nagain<\/strong> hold up the metal screen<\/strong>. Light<\/strong> does not pass<\/strong> through, but heat<\/strong>\ndoes. Substitute for the metal a very thin tank<\/strong> filled with a solution\nof alum, and then light passes<\/strong>, but heat<\/strong> is cut off. So that heat<\/strong> and\nelectricity<\/strong> _both_ penetrate what is impenetrable to light<\/strong>; while\nlight forces<\/strong> a passage securely barred against both electricity<\/strong> and\nheat<\/strong>. And we must remember<\/strong> that open space conveys<\/strong> all alike from the\nsun to the earth.<\/phrase>","solid matter<\/word>","rapid succession<\/word>","continue<\/word>","hand<\/word>","slow<\/word>","long waves<\/word>","rapid shakes<\/word>","other words<\/word>","many bodies<\/word>","several varieties<\/word>","such thing<\/word>","absolute resistance<\/word>","delicate instruments<\/word>","On meeting what we call<\/strong> solid matter<\/strong>, ether<\/strong> waves are influenced, not\nbecause ether<\/strong> is wanting in the solid matter<\/strong>, but because the presence\nof something else than ether<\/strong> affects the intervening ether<\/strong> itself.\nConsequently glass, to take an instance, so affects ether<\/strong> that a very\nrapid succession<\/strong> of waves (light<\/strong>) are able to continue<\/strong> their way\nthrough its interstices, whereas long<\/strong> electric waves<\/strong> are so hampered\nthat they die out altogether. Metal on the other hand<\/strong> welcomes slow<\/strong>\nvibrations (_i.e._ long waves<\/strong>), but speedily kills the rapid shakes<\/strong> of\nlight<\/strong>. In other words<\/strong>, _transparency_ is not confined to light<\/strong> alone.\nAll bodies are transparent to some variety of rays, and many bodies<\/strong> to\nseveral varieties<\/strong>. It may perhaps even be proved that there is no\nsuch thing<\/strong> as absolute resistance<\/strong>, and that our inability to detect<\/strong>\npenetration is due to lack of sufficiently delicate instruments<\/strong>.<\/phrase>","cardinal points<\/word>","The cardinal points<\/strong> to be remembered are these:--<\/phrase>","universal medium<\/word>","That the ether<\/strong> is a universal medium<\/strong>, conveying all kinds and forms of\nenergy.<\/phrase>","energy differ<\/word>","That these forms of energy differ<\/strong> only in their rates of vibration.<\/phrase>","vibration determines<\/word>","That the rate of vibration determines<\/strong> what power of penetration the\nwaves shall have through any given substance.<\/phrase>","whereas matter<\/word>","close<\/word>","gentle warmth<\/word>","electric circuit<\/word>","current capable<\/word>","spark<\/word>","Metal wires<\/word>","electrical tubes<\/word>","speaking tube<\/word>","electric ear<\/word>","Now, it is generally true that whereas matter<\/strong> of any kind offers\nresistance to light<\/strong>--that is, is not so perfect a conductor as the\nether<\/strong>--many substances, especially metals, are more sensitive than\nether<\/strong> to heat<\/strong> and electricity<\/strong>. How quickly a spoon inserted into a hot\ncup of tea becomes uncomfortably hot, though the hand<\/strong> can be held very\nclose<\/strong> to the liquid without feeling more than a gentle warmth<\/strong>. And we\nall have noticed that the very least air-gap in an electric circuit<\/strong>\neffectively breaks a current capable<\/strong> of traversing miles of wire. If\nthe current is so intense that it insists on passing the gap, it leaps\nacross with a report<\/strong>, making a spark<\/strong> that is at once intensely bright\nand hot. Metal wires<\/strong> are to electricity<\/strong> what speaking tubes are to\nsound<\/strong>; they are as it were electrical tubes<\/strong> through the air and ether<\/strong>.\nBut just as a person listening outside a speaking tube<\/strong> might faintly\nhear the sounds passing through it, so an instrument gifted with an\n\"electric ear<\/strong>\" would detect<\/strong> the currents passing through the wire.\nWireless telegraphy<\/strong> is possible because mankind has discovered\ninstruments which act as _electric ears or eyes_, catching and\nrecording vibrations that had hitherto remained undetected.<\/phrase>","known form<\/word>","fire<\/word>","incredible velocity<\/word>","The earliest known form<\/strong> of wireless telegraphy<\/strong> is transmission of\nmessages by light<\/strong>. A man<\/strong> on a hill lights a lamp or a fire<\/strong>. This\nrepresents his instrument for agitating the ether<\/strong> into waves, which\nproceed straight ahead with incredible velocity<\/strong> until they reach<\/strong> the\nreceiver, the eye of a man<\/strong> watching at a point<\/strong> from which the light<\/strong> is\nvisible.<\/phrase>","electric telegraphy<\/word>","Then came electric telegraphy<\/strong>.<\/phrase>","complete circuit<\/word>","earth connection<\/word>","metallic circuit<\/word>","At first a complete circuit<\/strong> (two wires) was used. But in 1838 it was\ndiscovered that if instead of two wires only one was used, the other\nbeing replaced by an earth connection<\/strong>, not only was the effect equally\npowerful, but even double<\/strong> of what it was with the metallic circuit<\/strong>.<\/phrase>","first step<\/word>","Thus<\/strong> the first step<\/strong> had been taken towards wireless electrical\ntelegraphy.<\/phrase>","other wire<\/word>","The second was, of course, to abolish the other wire<\/strong>.<\/phrase>","Professor Morse<\/word>","sent signals<\/word>","Susquehanna River<\/word>","metallic connections<\/word>","one wire<\/word>","receiving instrument<\/word>","large copper plate sunk<\/word>","water<\/word>","enough messages<\/word>","indefinite distance<\/word>","current passing<\/word>","large portion<\/word>","This was first effected by Professor Morse<\/strong>, who, in 1842, sent signals<\/strong>\nacross the Susquehanna River<\/strong> without metallic connections<\/strong> of any sort.\nAlong each bank of the river was stretched a wire three times as long<\/strong>\nas the river was broad. In the one wire<\/strong> a battery and transmitter were\ninserted, in the other a receiving instrument<\/strong> or galvanometer. Each\nwire terminated at each end<\/strong> in a large copper plate sunk<\/strong> in the water<\/strong>.\nMorse's conclusions were that provided the wires were long<\/strong> enough and\nthe plates large enough messages<\/strong> could be transmitted for an\nindefinite distance<\/strong>; the current passing<\/strong> from plate to plate, though a\nlarge portion<\/strong> of it would be lost in the water<\/strong>.[1]<\/phrase>","observe<\/word>","electrical systems<\/word>","meant telegraphy<\/word>","improved methods<\/word>","[1] It is here proper to observe<\/strong> that the term _wireless_\n telegraphy, as applied to electrical systems<\/strong>, is misleading,\n since it implies the absence of wires; whereas in all systems\n wires are used. But since it is generally understood that by\n wireless telegraphy<\/strong> is meant telegraphy<\/strong> without _metal\n connections_, and because the more improved methods<\/strong> lessen more\n and more the amount of wire used, the phrase has been allowed\n to stand.<\/phrase>","same date<\/word>","Scotchman<\/word>","James Bowman Lindsay of Dundee<\/word>","intellectual attainments<\/word>","similar manner<\/word>","River Tay<\/word>","September<\/word>","Association at Dundee<\/word>","Great Britain<\/word>","square feet<\/word>","immersed sheets<\/word>","coil<\/word>","Want<\/word>","poor scholar<\/word>","obtain<\/word>","public support<\/word>","face<\/word>","electrical discoveries<\/word>","gigantic dictionary<\/word>","fifty<\/word>","About the same date<\/strong> a Scotchman<\/strong>, James Bowman Lindsay of Dundee<\/strong>, a man<\/strong>\nas rich in intellectual attainments<\/strong> as he was pecuniarily poor, sent\nsignals in a similar manner<\/strong> across the River Tay<\/strong>. In September<\/strong>, 1859,\nLindsay read a paper before the British Association at Dundee<\/strong>, in\nwhich he maintained that his experiments and calculations assured him\nthat by running wires along the coasts of America and Great Britain<\/strong>,\nby using a battery having an acting surface of 130 square feet<\/strong> and\nimmersed sheets<\/strong> of 3000 square feet<\/strong>, and a coil<\/strong> weighing 300 lbs., he\ncould send messages from Britain to America. Want<\/strong> of money prevented\nthe poor scholar<\/strong> of Dundee from carrying out his experiments on a\nlarge enough scale to obtain<\/strong> public support<\/strong>. He died in 1862, leaving\nbehind him the reputation of a man<\/strong> who in the face<\/strong> of the greatest\ndifficulties made extraordinary electrical discoveries<\/strong> at the cost of\nunceasing labour; and this in spite of the fact that he had undertaken\nand partly executed a gigantic dictionary<\/strong> in fifty<\/strong> different\nlanguages!<\/phrase>","[Illustration: _M. Marconi's Travelling Station for Wireless\nTelegraphy._]<\/phrase>","electrical signals<\/word>","Hertzian waves<\/word>","The transmission of electrical signals<\/strong> through matter<\/strong>, metal, earth,\nor water<\/strong>, is effected by _conduction_, or the _leading_ of the\ncurrents in a circuit. When we come to deal with a\u00ebrial transmission,\n_i.e._ where one or both wires are replaced by the ether<\/strong>, then two\nmethods are possible, those of _induction_ and Hertzian waves<\/strong>.<\/phrase>","induction method<\/word>","wire magnetism<\/word>","magnetic field<\/word>","magnetic waves<\/word>","extend<\/word>","electrified wire<\/word>","Wherever<\/word>","telephone<\/word>","To take the induction method<\/strong> first. Whenever a current is sent through\na wire magnetism<\/strong> is set up in the ether<\/strong> surrounding the wire, which\nbecomes the core of a \"magnetic field<\/strong>.\" The magnetic waves<\/strong> extend<\/strong> for\nan indefinite distance<\/strong> on all sides, and on meeting a wire _parallel_\nto the electrified wire<\/strong> _induce_ in it a _dynamical_ current similar\nto that which caused them. Wherever<\/strong> electricity<\/strong> is present<\/strong> there is\nmagnetism also, and _vice vers\u00e2_. Electricity<\/strong>--produces\nmagnetism--produces electricity<\/strong>. The invention of the Bell<\/strong> telephone<\/strong>\nenabled telegraphers to take advantage of this law.<\/phrase>","Sir William Preece<\/word>","electrical engineer<\/word>","General Post-Office<\/word>","Newcastle<\/word>","mile apart<\/word>","parallel telegraph<\/word>","regular communication<\/word>","Flatholm<\/word>","island fort<\/word>","Bristol Channel<\/word>","Welsh<\/word>","coast<\/word>","3-1\/3 miles<\/word>","In 1885 Sir William Preece<\/strong>, now consulting electrical engineer<\/strong> to the\nGeneral Post-Office<\/strong>, erected near Newcastle<\/strong> two insulated squares of\nwire, each side 440 yards long<\/strong>. The squares were horizontal, parallel,\nand a quarter of a mile apart<\/strong>. On currents being sent through the one,\ncurrents were detected in the other by means of a telephone<\/strong>, which\nremained active even when the squares were separated by 1000 yards.\nSir William Preece<\/strong> thus<\/strong> demonstrated that signals could be sent\nwithout even an earth connection<\/strong>, _i.e._ entirely through the ether<\/strong>.\nIn 1886 he sent signals<\/strong> between two parallel telegraph<\/strong> wires 4-1\/2\nmiles apart. And in 1892 established a regular communication<\/strong> between\nFlatholm<\/strong>, an island fort<\/strong> in the Bristol Channel<\/strong>, and Lavernock, a\npoint<\/strong> on the Welsh<\/strong> coast<\/strong> 3-1\/3 miles<\/strong> distant.<\/phrase>","inductive method<\/word>","greater successes<\/word>","formidable rival<\/word>","The inductive method<\/strong> might have attained to greater successes<\/strong> had not\na formidable rival<\/strong> appeared in the Hertzian waves<\/strong>.<\/phrase>","Professor Hertz<\/word>","Leyden<\/word>","complete circle<\/word>","electric eye<\/word>","screw<\/word>","certain width<\/word>","great facts<\/word>","In 1887 Professor Hertz<\/strong> discovered that if the discharge from a Leyden<\/strong>\njar were passed through wires containing an air-gap across which the\ndischarge had to pass<\/strong>, sparks would also pass<\/strong> across a gap in an\nalmost complete circle<\/strong> or square of wire held at some distance from\nthe jar. This \"electric eye<\/strong>,\" or detector, could have its gap so\nregulated by means of a screw<\/strong> that at a certain width<\/strong> its effect would\nbe most pronounced, under which condition the detector, or receiver,\nwas \"in tune\" with the exciter, or transmitter. Hertz thus<\/strong> established\nthree great facts<\/strong>, that--<\/phrase>","(_a_) A discharge of static (_i.e._ collected) electricity<\/strong>\n across an air-gap produced strong electric waves<\/strong> in the ether<\/strong>\n on all sides.<\/phrase>","(_b_) That these waves could be _caught_.<\/phrase>","certain conditions<\/word>","(_c_) That under certain conditions<\/strong> the catcher worked most\n effectively.<\/phrase>","latest phase<\/word>","Signor Marconi<\/word>","Professors Branly of Paris<\/word>","Popoff of Cronstadt<\/word>","many others<\/word>","improved means<\/word>","Out of these three discoveries has sprung the latest phase<\/strong> of wireless\ntelegraphy, as exploited by Signor Marconi<\/strong>. He, in common with\nProfessors Branly of Paris<\/strong>, Popoff of Cronstadt<\/strong>, and Slaby of\nCharlottenburg, besides many others<\/strong>, have devoted their attention to\nthe production of improved means<\/strong> of sending and receiving the Hertzian\nwaves. Their experiments have shown that two things are required in\nwireless telegraphy<\/strong>--<\/phrase>","(i.) That the waves shall have great penetrating power, so as\n to pierce any obstacle.<\/phrase>","original force<\/word>","(ii.) That they shall retain their energy, so that a _maximum_\n of their original force<\/strong> shall reach<\/strong> the receiver.<\/phrase>","first condition<\/word>","great length<\/word>","greatest frequency<\/word>","telegraphic results<\/word>","light waves<\/word>","many thousands<\/word>","1-1\/2 yards<\/word>","The first condition<\/strong> is fulfilled best by waves of great length<\/strong>; the\nsecond by those which, like<\/strong> light<\/strong>, are of greatest frequency<\/strong>. For best\ntelegraphic results<\/strong> a compromise must be effected between these\nextremes, neither the thousand-mile long waves<\/strong> of an alternating\ndynamo nor the light waves<\/strong> of many thousands<\/strong> to an inch being of use<\/strong>.\nThe Hertzian waves<\/strong> are estimated to be 230,000,000 per second; at\nwhich rate they would be 1-1\/2 yards<\/strong> long<\/strong>. They vary considerably,\nhowever, on both sides of this rate and dimension.<\/phrase>","brass balls<\/word>","many millions<\/word>","found<\/word>","aluminium wire<\/word>","Marconi's transmitter consists of three parts--a battery; an induction\ncoil<\/strong>, terminating in a pair of brass balls<\/strong>, one on each side of the\nair-gap; and a Morse transmitting-key. Upon the key being depressed, a\ncurrent from the battery passes through the coil<\/strong> and accumulates\nelectricity<\/strong> on the brass balls<\/strong> until its tension causes it to leap\nfrom one to the other many millions<\/strong> of times in what is called a\nspark<\/strong>. The longer the air-gap the greater must be the accumulation\nbefore the leap takes place<\/strong>, and the greater the power of the\nvibrations set up. Marconi found<\/strong> that by connecting a kite or balloon\ncovered with tinfoil by an aluminium wire<\/strong> with one of the balls, the\neffect of the waves was greatly increased. Sometimes he replaced the\nkite or balloon by a conductor placed on poles two or three hundred\nfeet high, or by the mast of a ship.<\/phrase>","turn<\/word>","We now turn<\/strong> to the receiver.<\/phrase>","several feet<\/word>","simplest form<\/word>","loose connection<\/word>","flow<\/word>","metal microphone stuck<\/word>","carbon microphone<\/word>","former position<\/word>","loose contact<\/word>","wave effect<\/word>","In 1879 Professor D. E. Hughes observed that a microphone, in\nconnection with a telephone<\/strong>, produced sounds in the latter even when\nthe microphone was at a distance of several feet<\/strong> from coils through\nwhich a current was passing. A microphone, it may be explained, is in\nits simplest form<\/strong> a loose connection<\/strong> in an electric circuit<\/strong>, which\ncauses the current to flow<\/strong> in fits and starts at very frequent\nintervals. He discovered that a metal microphone stuck<\/strong>, or cohered,\nafter a wave<\/strong> had influenced it, but that a carbon microphone<\/strong> was\nself-restoring, _i.e._ regained its former position<\/strong> of loose contact<\/strong>\nas soon as a wave effect<\/strong> had ceased.<\/phrase>","Professor Branly of Paris<\/word>","name<\/word>","own<\/word>","In 1891 Professor Branly of Paris<\/strong> produced a \"coherer,\" which was\nnothing more than a microphone under another name<\/strong>. Five years later\nMarconi somewhat altered Branly's contrivance, and took out a patent\nfor a coherer of his own<\/strong>.<\/phrase>","tiny glass tube<\/word>","wire enters<\/word>","silver plugs<\/word>","bore<\/word>","special filings<\/word>","merest trace<\/word>","It is a tiny glass tube<\/strong>, about two inches long<\/strong> and a tenth of an inch\nin diameter inside. A wire enters<\/strong> it at each end<\/strong>, the wires\nterminating in two silver plugs<\/strong> fitting the bore<\/strong> of the tube. A space\nof 1\/32 inch is left between the plugs, and this space is filled with\nspecial filings<\/strong>, a mixture of 96 parts of nickel to 4 of silver, and\nthe merest trace<\/strong> of mercury. The tube is exhausted of almost all its\nair before being sealed.<\/phrase>","little gap<\/word>","electric wave<\/word>","practical purposes<\/word>","metal particles<\/word>","offer<\/word>","great resistance<\/word>","This little gap<\/strong> filled with filings is, except when struck by an\nelectric wave<\/strong>, to all practical purposes<\/strong> a non-conductor of\nelectricity<\/strong>. The metal particles<\/strong> touch<\/strong> each other so lightly that they\noffer<\/strong> great resistance<\/strong> to a current.<\/phrase>","Hertzian wave<\/word>","press<\/word>","succeeding wave<\/word>","long paper tape<\/word>","But when a Hertzian wave<\/strong> flying through the ether<\/strong> strikes the coherer,\nthe particles suddenly press<\/strong> hard on one another, and make a bridge\nthrough which a current can pass<\/strong>. The current works a \"relay,\" or\ncircuit through which a stronger current passes<\/strong>, opening and closing\nit as often as the coherer is influenced by a wave<\/strong>. The relay actuates\na tapper that gently taps the tube after each wave<\/strong>-influence, causing\nthe particles to _de_cohere in readiness for the succeeding wave<\/strong>, and\nalso a Morse instrument for recording words in dots and dashes on a\nlong paper tape<\/strong>.<\/phrase>","move<\/word>","work<\/word>","The coherer may be said to resemble an engine-driver, and the \"relay\"\nan engine. The driver is not sufficiently strong to himself move<\/strong> a\ntrain<\/strong>, but he has strength enough to turn<\/strong> on steam and make the engine\ndo the work<\/strong>. The coherer is not suitable for use<\/strong> with currents of the\nintensity required to move<\/strong> a Morse recorder, but it easily switches a\npowerful current into another circuit.<\/phrase>","space forbids<\/word>","detailed account<\/word>","improved instruments<\/word>","appended list<\/word>","serve<\/word>","Want<\/strong> of space forbids<\/strong> a detailed account<\/strong> of Marconi's successes with\nhis improved instruments<\/strong>, but the appended list<\/strong> will serve<\/strong> to show\nhow he gradually increased the distance over which he sent signals<\/strong>\nthrough space.<\/phrase>","England<\/word>","Salisbury Plain<\/word>","In 1896 he came to England<\/strong>. That year he signalled from a room in the\nGeneral Post-Office<\/strong> to a station on the roof 100 yards distant.\nShortly afterwards he covered 2 miles on Salisbury Plain<\/strong>.<\/phrase>","Lavernock Point<\/word>","critical time<\/word>","same gap<\/word>","newer system<\/word>","happy inspiration<\/word>","greater length<\/word>","Brean Down<\/word>","other side<\/word>","8-2\/3 miles<\/word>","In May, 1897, he sent signals<\/strong> from Lavernock Point<\/strong> to Flatholm<\/strong>, 3-1\/3\nmiles. This success occurred at a critical time<\/strong>, for Sir W. Preece had\nalready, as we have seen, bridged the same gap<\/strong> by his induction\nmethod, and for three days Marconi failed to accomplish the feat with\nhis apparatus, so that it appeared as though the newer system<\/strong> were the\nless effective of the two. But by carrying the transmitting instrument\non to the beach below the cliff on which it had been standing, and\njoining it by a wire to the pole already erected on the top of the\ncliff, Mr. Marconi, thanks to a happy inspiration<\/strong>, did just what was\nneeded; he got a greater length<\/strong> of wire to send off his waves from.\nCommunication was at once established with Flatholm<\/strong>, and on the next\nday with Brean Down<\/strong>, on the other side<\/strong> of the Bristol Channel<\/strong>, and\n8-2\/3 miles<\/strong> distant. Then we have--<\/phrase>","Needles Hotel<\/word>","17-1\/2 miles<\/word>","Bath<\/word>","Harwich<\/word>","Isle of Wight<\/word>","Lizard<\/word>","Dec<\/word>","Needles Hotel<\/strong> to Swanage 17-1\/2 miles<\/strong>.\n Salisbury to Bath<\/strong> 34 \"\n French Coast<\/strong> to Harwich<\/strong> 90 \"\n Isle of Wight<\/strong> to The Lizard<\/strong> 196 \"\n At Sea (1901) 350 \"\n Dec<\/strong>. 17, 1901, England<\/strong> to America 2099 \"<\/phrase>","Limited<\/word>","transatlantic wireless telegraphy<\/word>","rial wires<\/word>","[Illustration: _Poldhu Towers, the Station put down by the Marconi\nWireless Telegraph Company, Limited<\/strong>, for carrying on a system of\ntransatlantic wireless telegraphy<\/strong> between England<\/strong> and America. From\nthe four towers are suspended the \u00e6rial wires<\/strong> which are carried into\nthe buildings in the centre. The towers are 215 feet in height, and\nare made of wood._]<\/phrase>","February<\/word>","Cornwall<\/word>","sufficient strength<\/word>","reply<\/word>","A more pronounced, though perhaps less sensational, success than even\nthis last<\/strong> occurred at the end<\/strong> of February<\/strong>, 1902. Mr. Marconi, during a\nvoyage to America on the s.s. _Philadelphia_ remained in communication\nwith Poldhu, Cornwall<\/strong>, until the vessel was 1550 miles distant,\nreceiving messages on a Morse recorder for any one acquainted with the\ncode to read. Signals arrived for a further 500 miles, but owing to\nhis instruments not being of sufficient strength<\/strong>, Mr. Marconi could\nnot reply<\/strong>.<\/phrase>","transatlantic achievement<\/word>","whole system<\/word>","weak points<\/word>","When the transatlantic achievement<\/strong> was announced at the end<\/strong> of 1901,\nthere was a tendency in some quarters to decry the whole system<\/strong>. The\ncritics laid their fingers on two weak points<\/strong>.<\/phrase>","good working rate<\/word>","twenty-two words<\/word>","further increase<\/word>","In the first place<\/strong>, they said, the speed at which the messages could\nbe transmitted was too slow<\/strong> to insure that the system would pay. Mr.\nMarconi replied that there had been a time<\/strong> when one word per minute\nwas considered a good working rate<\/strong> across the Atlantic<\/strong> cable; whereas\nhe had already sent twenty-two words<\/strong> per minute over very long<\/strong>\ndistances. A further increase<\/strong> of speed was only a matter<\/strong> of time<\/strong>.<\/phrase>","second objection<\/word>","many sets<\/word>","The second objection<\/strong> raised centred on the lack of secrecy resulting\nfrom signals being let loose into space to strike any instrument\nwithin their range; and also on the confusion that must arise when the\nether<\/strong> was traversed by many sets<\/strong> of electric waves<\/strong>.<\/phrase>","Italian inventor<\/word>","experiments aware<\/word>","parabolic metal screens<\/word>","required direction<\/word>","prevent<\/word>","certain length<\/word>","The young Italian inventor<\/strong> had been throughout his experiments aware<\/strong>\nof these defects and sought means to remedy them. In his earliest\nattempts we find him using parabolic metal screens<\/strong> to project his\nwaves in any required direction<\/strong> and prevent<\/strong> their going in any other.\nHe also employed strips of metal in conjunction with the coherer, the\nstrips or \"wings\" being of such a size as to respond most readily to\nwaves of a certain length<\/strong>.<\/phrase>","electric oscillations<\/word>","aerial wires<\/word>","great power<\/word>","loud noise<\/word>","notes results<\/word>","same pitch<\/word>","The electric oscillations<\/strong> coming from the aerial wires<\/strong> carried on\npoles, kites, &c., were of great power<\/strong>, but their energy dispersed\nvery quickly into space in a series of rapidly diminishing vibrations.\nThis fact made them affect to a greater or less degree any receiver\nthey might encounter on their wanderings. If you go into a room where\nthere is a piano and make a loud noise<\/strong> near the instrument a jangle of\nnotes results<\/strong>. But if you take a tuning-fork and after striking it\nplace<\/strong> it near the strings, only one string will respond, _i.e._ that\nof the same pitch<\/strong> as the fork.<\/phrase>","note<\/word>","What is required in wireless telegraphy<\/strong> is a system corresponding to\nthe use<\/strong> of the tuning-fork. Unfortunately, it has been discovered that\nthe syntony or tuning of transmitter and receiver reduces the distance\nover which they are effective. An electric \"noise\" is more\nfar-reaching than an electric \"note<\/strong>.\"<\/phrase>","considerable advances towards<\/word>","tuning system<\/word>","great regularity<\/word>","produce<\/word>","sufficient power<\/word>","Mr. Marconi has, however, made considerable advances towards<\/strong> combining\nthe sympathy and secrecy of the tuning system<\/strong> with the power of the\n\"noise\" system. By means of delicately adjusted \"wings\" and coils he\nhas brought it about that a series of waves having small individual\nstrength, but great regularity<\/strong>, shall produce<\/strong> on the receiver a\n_cumulative_ effect, storing, as it were, electricity<\/strong> on the surface\nof the receiver \"wings\" until it is of sufficient power<\/strong> to overcome\nthe resistance of the coherer.<\/phrase>","moderate distances<\/word>","open<\/word>","lock<\/word>","discover<\/word>","right tune<\/word>","syntonic messages<\/word>","That tuned wireless telegraphy<\/strong> is, over moderate distances<\/strong>, at least\nas secret as that through wires (which can be tapped by induction) is\nevident from the fact that during the America Cup Yacht Races Mr.\nMarconi sent daily to the _New York Herald_ messages of 4000 total\nwords, and kept them private in spite of all efforts to intercept\nthem. He claims to have as many as 250 \"tunes\"; and, indeed, there\nseems to be no limit to their number<\/strong>, so that the would-be \"tapper\" is\nin the position of a man<\/strong> trying to open<\/strong> a letter-lock<\/strong> of which he does\nnot know the cipher-word. He _may_ discover<\/strong> the right tune<\/strong>, but the\nchances are greatly against him. We may be certain that the rapid\nadvance in wireless telegraphy<\/strong> will not proceed much further before\nsyntonic messages<\/strong> can be transmitted over hundreds if not thousands of\nmiles.<\/phrase>","great prospect<\/word>","present network<\/word>","land<\/word>","fixed objects<\/word>","metallic circuits<\/word>","It is hardly necessary to dwell upon the great prospect<\/strong> that the new\ntelegraphy opens to mankind. The advantages arising out of a ready\nmeans of communication, freed from the shackles of expensive\nconnecting wires and cables are, in the main, obvious enough. We have\nonly to imagine<\/strong> all the present network<\/strong> of wires replaced or\nsupplemented by ether<\/strong>-waves, which will be able to act between points\n(_e.g._ ships and ships, ships and land<\/strong>, moving and fixed objects<\/strong>\ngenerally) which cannot be connected by metallic circuits<\/strong>.<\/phrase>","ocean voyages<\/word>","transatlantic journey<\/word>","newsless period<\/word>","play<\/word>","part<\/word>","big guns<\/word>","naval war<\/word>","maritime nation<\/word>","great empire<\/word>","electric links<\/word>","Already ocean voyages<\/strong> are being shortened as regards the time<\/strong> during\nwhich passengers are out of contact with the doings of the world. The\ntransatlantic journey<\/strong> has now a newsless period<\/strong> of but three days.\nNavies are being fitted out with instruments that may play<\/strong> as\nimportant a part<\/strong> as the big guns<\/strong> themselves in the next naval war<\/strong>. A\ngreat maritime nation<\/strong> like<\/strong> our own<\/strong> should be especially thankful that\nthe day is not far distant when our great empire<\/strong> will be connected by\ninvisible electric links<\/strong> that no enemy may discover<\/strong> and cut.<\/phrase>","romantic side<\/word>","Professor Ayrton<\/word>","The romantic side<\/strong> of wireless telegraphy<\/strong> has been admirably touched in\nsome words uttered by Professor Ayrton<\/strong> in 1899, after the reading of a\npaper by Mr. Marconi before the Institution of Electrical Engineers.<\/phrase>","electro-magnetic voice<\/word>","electro-magnetic ear<\/word>","\"If a person wished to call<\/strong> to a friend\" (said the Professor), \"he\nwould use<\/strong> a loud electro-magnetic voice<\/strong>, audible only to him who had\nthe electro-magnetic ear<\/strong>.<\/phrase>","\"'Where are you?' he would say.<\/phrase>","coal mine<\/word>","Andes<\/word>","Pacific<\/word>","\"The reply<\/strong> would come--'I am at the bottom of a coal mine<\/strong>,' or\n'Crossing the Andes<\/strong>,' or 'In the middle of the Pacific<\/strong>.' Or, perhaps,\nin spite of all the calling, no reply<\/strong> would come, and the person would\nthen know his friend was dead. Let them think of what that meant; of\nthe calling which went on every day from room to room of a house,\nand then imagine<\/strong> that calling extending from pole to pole; not a noisy\nbabble, but a call<\/strong> audible to him who wanted to hear and absolutely\nsilent to him who did not.\"<\/phrase>","[Illustration: _Guglielmo Marconi._]<\/phrase>","forecast come<\/word>","ordinary man wonders<\/word>","fear<\/word>","next development<\/word>","Lord Kelvin<\/word>","confess<\/word>","inner workings<\/word>","Nature<\/word>","When will Professor Ayrton<\/strong>'s forecast come<\/strong> true? Who can say? Science<\/strong>\nis so full of surprises that the ordinary man wonders<\/strong> with a semi-fear<\/strong>\nwhat may be the next development<\/strong>; and wise men like<\/strong> Lord Kelvin<\/strong> humbly\nconfess<\/strong> that in comparison with what has yet to be learnt about the\nmysterious inner workings<\/strong> of Nature<\/strong> their knowledge is but as\nignorance.<\/phrase>","HIGH-SPEED TELEGRAPHY.<\/phrase>","wonderful developments<\/word>","startling improvements<\/word>","ordinary wire-circuit method<\/word>","The wonderful developments<\/strong> of wireless telegraphy<\/strong> must not make us\nforget that some very interesting and startling improvements<\/strong> have been\nmade in connection with the ordinary wire-circuit method<\/strong>: notably in\nthe matter<\/strong> of speed.<\/phrase>","certain seasons<\/word>","special circumstances<\/word>","great rush<\/word>","important towns<\/word>","fifty words<\/word>","contain<\/word>","brief period<\/word>","At certain seasons<\/strong> of the year or under special circumstances<\/strong> which\ncan scarcely be foreseen, a great rush<\/strong> takes place<\/strong> to transmit\nmessages over the wires connecting important towns<\/strong>. Now, the best\ntelegraphists can with difficulty keep up a transmitting speed of even\nfifty words<\/strong> a minute for so long<\/strong> as half-an-hour. The Morse alphabet\ncontains on the average three signals for each letter, and the average\nlength of a word is six letters. Fifty words<\/strong> would therefore contain<\/strong>\nbetween them 900 signals, or fifteen a second. The strain of sending\nor noting so many for even a brief period<\/strong> is very wearisome to the\noperator.<\/phrase>","telegraph clerk<\/word>","actual signalling<\/word>","mechanical devices<\/word>","Means have been found<\/strong> of replacing the telegraph clerk<\/strong>, so far as the\nactual signalling<\/strong> is concerned, by mechanical devices<\/strong>.<\/phrase>","Alexander Bain<\/word>","Thurso<\/word>","chemical telegraph<\/word>","large metal type<\/word>","negative pole<\/word>","brush<\/word>","metal type<\/word>","receiving station<\/word>","similar brush<\/word>","similar speed<\/word>","strip<\/word>","white spaces<\/word>","contact points<\/word>","In 1842 Alexander Bain<\/strong>, a watchmaker of Thurso<\/strong>, produced what is known\nas a \"chemical telegraph<\/strong>.\" The words to be transmitted were set up in\nlarge metal type<\/strong>, all capitals, connected with the positive pole<\/strong> of\na battery, the negative pole<\/strong> of which was connected to earth. A metal\nbrush<\/strong>, divided into five points, each terminating a wire, was passed\nover the metal type<\/strong>. As often as a division of the brush<\/strong> touched metal\nit completed the electric circuit<\/strong> in the wire to which it was joined,\nand sent a current to the receiving station<\/strong>, where a similar brush<\/strong> was\npassing at similar speed<\/strong> over a strip<\/strong> of paper soaked in iodide of\npotassium. The action of the electricity<\/strong> decomposed the solution,\nturning it blue or violet. The result was a series of letters divided\nlongitudinally into five belts separated by white spaces<\/strong> representing\nthe intervals between the contact points<\/strong> of the brush<\/strong>.<\/phrase>","high-speed system<\/word>","[Illustration: _The receiving instrument<\/strong> used by Messrs. Pollak &\nVirag in their high-speed system<\/strong> of telegraphy. This instrument is\ncapable of receiving and photographically recording messages at the\nastonishing speed of 50,000 words an hour._]<\/phrase>","Bain Chemical Telegraph<\/word>","enormous number<\/word>","ten times<\/word>","general use<\/word>","The Bain Chemical Telegraph<\/strong> was able to transmit the enormous number<\/strong>\nof 1500 words per minute; that is, at ten times<\/strong> the rate of ordinary\nconversation! But even when improvements had reduced the line wires\nfrom five to one, the system, on account of the method of composing\nthe message to be sent, was not found<\/strong> sufficiently practical to come\ninto general use<\/strong>.<\/phrase>","preferable systems<\/word>","multiplex telegraphy<\/word>","Its place<\/strong> was taken by slower but preferable systems<\/strong>: those of duplex\nand multiplex telegraphy<\/strong>.<\/phrase>","actual time<\/word>","more messages<\/word>","same wire<\/word>","When a message is sent over the wires, the actual time<\/strong> of making the\nsignals is more than is required for the current to pass<\/strong> from place<\/strong> to\nplace<\/strong>. This fact has been utilised by the inventors of methods whereby\ntwo or more messages<\/strong> may not only be sent the _same_ way along the\nsame wire<\/strong>, but may also be sent in _different_ directions. Messages\nare \"duplex\" when they travel<\/strong> across one another, \"multiplex\" when\nthey travel<\/strong> together.<\/phrase>","several instruments<\/word>","The principle whereby several instruments<\/strong> are able to use<\/strong> the same\nwire is that of _distributing_ among the instruments the time<\/strong> during\nwhich they are in contact with the line.<\/phrase>","Edinburgh<\/word>","Let us suppose<\/strong> that four transmitters are sending messages\nsimultaneously from London<\/strong> to Edinburgh<\/strong>.<\/phrase>","circular contact-maker<\/word>","insulated segments<\/word>","Wires from all four instruments are led into a circular contact-maker<\/strong>,\ndivided into some hundreds of insulated segments<\/strong> connected in rotation\nwith the four transmitters. Thus<\/strong> instrument A will be joined to\nsegments 1, 5, 9, 13; instrument B to segments 2, 6, 10, 14;\ninstrument C with segments 3, 7, 11, 15; and so on.<\/phrase>","uniform rate<\/word>","top speed<\/word>","fifteen signals<\/word>","Along the top of the segments an arm, connected with the telegraph\nline to Edinburgh<\/strong>, revolves at a uniform rate<\/strong>. For about 1\/500 of a\nsecond it unites a segment with an instrument. If there are 150\nsegments on the \"distributor,\" and the arm revolves three times a\nsecond, each instrument will be put into contact with the line rather\noftener than 110 times per second. And if the top speed<\/strong> of fifty words<\/strong>\na minute is being worked to, each of the fifteen signals<\/strong> occurring in\neach second will be on the average divided among seven moments of\ncontact.<\/phrase>","similar apparatus<\/word>","escape<\/word>","revolving arms<\/word>","level speed<\/word>","cover<\/word>","same number<\/word>","greatest difficulty<\/word>","A similar apparatus<\/strong> at Edinburgh<\/strong> receives the messages. It is evident\nthat for the system to work<\/strong> satisfactorily, or even to escape<\/strong> dire\nconfusion, the revolving arms<\/strong> must run at a level speed<\/strong> in perfect\nunison with one another. When the London<\/strong> arm is over segment 1, the\nEdinburgh<\/strong> arm must cover<\/strong> the same number<\/strong>. The greatest difficulty<\/strong> in\nmultiplex telegraphy<\/strong> has been to adjust the timing exactly.<\/phrase>","Paul<\/word>","Cour of Copenhagen<\/word>","Phonic Wheel<\/word>","soft iron<\/word>","short distance<\/word>","nearest tooth<\/word>","regular series<\/word>","current impulses<\/word>","motor magnet<\/word>","easy matter<\/word>","Paul<\/strong> la Cour of Copenhagen<\/strong> invented for driving the arms a device\ncalled the Phonic Wheel<\/strong>, as its action was regulated by the vibrations\nof a tuning-fork. The wheel, made of soft iron<\/strong>, and toothed on its\ncircumference, revolves at a short distance<\/strong> from the pole of a magnet.\nAs often as a current enters the magnet the latter attracts the\nnearest tooth<\/strong> of the wheel; and if a regular series<\/strong> of currents pass<\/strong>\nthrough it the motion of the wheel will be uniform. M. la Cour\nproduced the regularity of current impulses<\/strong> in the motor magnet<\/strong> by\nmeans of a tuning-fork, which is unable to vibrate more than a certain\nnumber<\/strong> of times a second, and at each vibration closed a circuit\nsending current into the magnet. To get two tuning-forks of the same\nnote<\/strong> is an easy matter<\/strong>; and consequently a uniformity of rotation at\nboth London<\/strong> and Edinburgh<\/strong> stations may be insured.<\/phrase>","single wire<\/word>","huge saving<\/word>","separate conductors<\/word>","So sensitive is this \"interrupter\" system that as many as sixteen\nmessages can be sent simultaneously, which means that a single wire<\/strong> is\nconveying from 500 to 800 words a minute. We can easily understand the\nhuge saving<\/strong> that results from such a system; the cost of instruments,\ninterrupter, &c., being but small in proportion to that of a number<\/strong>\nof separate conductors<\/strong>.<\/phrase>","word-sending capacity<\/word>","automatic transmitters<\/word>","signal<\/word>","human brain<\/word>","Sir Charles Wheatstone<\/word>","Automatic Transmitter<\/word>","Post<\/word>","The word-sending capacity<\/strong> of a line may be even further increased by\nthe use<\/strong> of automatic transmitters<\/strong> able to work<\/strong> much faster in\nsignal<\/strong>-making than the human brain<\/strong> and hand<\/strong>. Sir Charles Wheatstone<\/strong>'s\nAutomatic Transmitter<\/strong> has long<\/strong> been used in the Post<\/strong>-Office\nestablishments.<\/phrase>","long tape<\/word>","parallel rows<\/word>","central row<\/word>","transmitting machine<\/word>","outside rows<\/word>","other determine<\/word>","left-hand hole<\/word>","right hand<\/word>","The messages to be sent are first of all punched on a long tape<\/strong> with\nthree parallel rows<\/strong> of perforations. The central row<\/strong> is merely for\nguiding the tape through the transmitting machine<\/strong>. The positions of\nthe holes in the two outside rows<\/strong> relatively to each other determine<\/strong>\nthe character of the signal<\/strong> to be sent. Thus<\/strong>, when three holes\n(including the central one) are abreast, a Morse \"dot\" is signified;\nwhen the left-hand hole<\/strong> is one place<\/strong> behind the right hand<\/strong>, a \"dash\"\nwill be telegraphed.<\/phrase>","long communication<\/word>","Half-a-dozen<\/word>","punch<\/word>","additional advantage<\/word>","In the case of a long communication<\/strong> the matter<\/strong> is divided among a\nnumber<\/strong> of clerks operating punching machines. Half-a-dozen<\/strong> operators\ncould between them punch<\/strong> holes representing 250 to 300 words a minute;\nand the transmitter is capable of despatching as many in the same\ntime<\/strong>, while it has the additional advantage<\/strong> of being tireless.<\/phrase>","punched tape<\/word>","The action of the transmitter is based upon the reversal of the\ndirection or nature<\/strong> of current. The punched tape<\/strong> is passed between an\noscillating lever, carrying two points, and plates connected with the\ntwo poles of the battery. As soon as a hole comes under a pin the pin\ndrops through and makes a contact.<\/phrase>","coil wound<\/word>","permanent bar-magnet<\/word>","north pole<\/word>","south pole<\/word>","few turns<\/word>","permanent magnet<\/word>","increase<\/word>","attractive power<\/word>","other direction<\/word>","At the receiving end<\/strong> the wire is connected with a coil wound<\/strong> round the\npole of a permanent bar-magnet<\/strong>. Such a magnet has what is known as a\nnorth pole<\/strong> and a south pole<\/strong>, the one attractive and the other\nrepulsive of steel or soft iron<\/strong>. Any bar of soft iron<\/strong> can be made\ntemporarily into a magnet by twisting round it a few turns<\/strong> of a wire\nin circuit with the poles of a battery. But which will be the north\nand which the south pole<\/strong> depends on the _direction_ of the current.\nIf, then, a current passes<\/strong> in one direction round the north pole<\/strong> of a\npermanent magnet<\/strong> it will increase<\/strong> the magnet's attractive power<\/strong>, but\nwill decrease it if sent in the other direction<\/strong>.<\/phrase>","abreast cause<\/word>","allow<\/word>","longer period<\/word>","marker rests<\/word>","unequal periods<\/word>","The \"dot\" holes punched in the tape being abreast cause<\/strong> first a\npositive and then a negative current following at a very short\ninterval; but the \"dash\" holes not being opposite allow<\/strong> the positive\ncurrent to occupy the wires for a longer period<\/strong>. Consequently the\nMorse marker rests<\/strong> for correspondingly unequal periods<\/strong> on the\nrecording \"tape,\" giving out a series of dots and dashes, as the inker\nis snatched quickly or more leisurely from the paper.<\/phrase>","multiplex method<\/word>","The Wheatstone recorder has been worked up to 400 words a minute, and\nwhen two machines are by the multiplex method<\/strong> acting together this\nrate is of course doubled.<\/phrase>","speed machine<\/word>","shade<\/word>","recent invention<\/word>","Hungarian electricians<\/word>","Anton Pollak<\/word>","Josef Virag<\/word>","perforated strip method<\/word>","telephonic diaphragm<\/word>","sensitised paper<\/word>","As a speed machine<\/strong> it has, however, been completely put in the shade<\/strong>\nby a more recent invention<\/strong> of two Hungarian electricians<\/strong>, Anton Pollak<\/strong>\nand Josef Virag<\/strong>, which combines the perforated strip method<\/strong> of\ntransmission with the telephone<\/strong> and photography. The message is sent\noff by means of a punched tape<\/strong>, and is recorded by means of a\ntelephonic diaphragm<\/strong> and light<\/strong> marking a sensitised paper<\/strong>.<\/phrase>","United Electrical Company of Buda-Pesth<\/word>","Hungarian capital<\/word>","double lines<\/word>","single circuit<\/word>","Pollak-Virag<\/word>","In 1898 the inventors made trials of their system for the benefit of\nthe United Electrical Company of Buda-Pesth<\/strong>. The Hungarian capital<\/strong> was\nconnected by two double lines<\/strong> of wire with a station 200 miles\ndistant, where the two sets were joined so as to give a single circuit<\/strong>\nof 400 miles in length. A series of tests in all weathers showed that\nthe Pollak-Virag<\/strong> system could transmit as many as 100,000 words an\nhour over that distance.<\/phrase>","Hungary<\/word>","United States<\/word>","sixty minutes<\/word>","Chicago<\/word>","odd miles<\/word>","From Hungary<\/strong> the inventors went to the United States<\/strong>, in which country\nof \"records\" no less than 155,000 words were despatched and received\nin the sixty minutes<\/strong>. This average--2580 words per minute, 43 per\nsecond--is truly remarkable! Even between New York and Chicago<\/strong>,\nseparated by 950 odd miles<\/strong>, the wires kept up an average of 1000 per\nminute.<\/phrase>","marvellous results<\/word>","type records messages<\/word>","clearly-written longhand characters<\/word>","The apparatus that produces these marvellous results<\/strong> is of two types.\nThe one type records messages<\/strong> in the Morse alphabet, the other makes\nclearly-written longhand characters<\/strong>. The former is the faster of the\ntwo, but the legibility of the other more than compensates for the\ndecrease of speed by one-half.<\/phrase>","receiving machine<\/word>","[Illustration: _Specimens of the punched tape<\/strong> used for transmitting\nmessages by the Pollak-Virag<\/strong> system, and of a message as it is\ndelivered by the receiving machine<\/strong>._]<\/phrase>","alphabet method<\/word>","The Morse alphabet method<\/strong> closely resembles the Wheatstone system. The\nmessage is prepared for transmission by being punched on a tape. But\nthere is this difference in the position of the holes, that whereas in\nthe Wheatstone method two holes are used for each dot and dash, only\none is required in the Pollak-Virag<\/strong>. If to the right of the central\nguiding line it signifies a \"dash,\" if to the left, a \"dot.\"<\/phrase>","receiver end<\/word>","attract<\/word>","fine metal bar<\/word>","tiny mirror<\/word>","slight movement<\/word>","exaggerated movement<\/word>","electric lamp<\/word>","bright spot<\/word>","The \"reversal-of-current\" method, already explained, causes at the\nreceiver end<\/strong> an increase<\/strong> or decrease in the power of a permanent\nmagnet to attract<\/strong> or repel a diaphragm, the centre of which is\nconnected by a very fine metal bar<\/strong> with the centre of a tiny mirror<\/strong>\nhinged at one side on two points. A very slight movement<\/strong> of the\ndiaphragm produces an exaggerated movement<\/strong> of the mirror, which, as it\ntilts backwards and forwards, reflects the light<\/strong> from an electric lamp<\/strong>\non to a lens, which concentrates the rays into a bright spot<\/strong>, and\nfocuses them on to a surface of sensitised paper<\/strong>.<\/phrase>","vertical cylinder<\/word>","lower end<\/word>","screw thread<\/word>","spiral path<\/word>","In their earliest apparatus the inventors attached the paper to the\ncircumference of a vertical cylinder<\/strong>, which revolved at an even pace\non an axle, furnished at the lower end<\/strong> with a screw thread<\/strong>, so that\nthe portion of paper affected by the light<\/strong> occupied a spiral path<\/strong> from\ntop to bottom of the cylinder.<\/phrase>","later edition<\/word>","endless band<\/word>","helical slit<\/word>","complete turn<\/word>","sensitised band<\/word>","spot<\/word>","light recommences<\/word>","left edge<\/word>","In a later edition<\/strong>, however, an endless band<\/strong> of sensitised paper<\/strong> is\nemployed, and the lamp is screened from the mirror by a horizontal\nmantle in which is cut a helical slit<\/strong> making one complete turn<\/strong> of the\ncylinder in its length. The mantle is rotated in unison with the\nmachinery driving the sensitised band<\/strong>; and as it revolves, the spot<\/strong> at\nwhich the light<\/strong> from the filament can pass<\/strong> through the slit to the\nmirror is constantly shifting from right to left, and the point<\/strong> at\nwhich the reflected light<\/strong> from the mirror strikes the sensitised paper<\/strong>\nfrom left to right. At the moment when a line is finished, the right\nextremity of the mantle begins to pass<\/strong> light<\/strong> again<\/strong>, and the bright\nspot<\/strong> of light recommences<\/strong> its work<\/strong> at the left edge<\/strong> of the band, which\nhas now moved on a space.<\/phrase>","mirror backwards<\/word>","record<\/word>","up-and-down strokes<\/word>","The movements of the mirror backwards<\/strong> and forwards produce<\/strong> on the\npaper a zigzag tracing known as syphon-writing. The record<\/strong>, which is\ncontinuous from side to side of the band, is a series of zigzag\nup-and-down strokes<\/strong>, corresponding to the dots and dashes of the Morse\nalphabet.<\/phrase>","longhand characters<\/word>","The apparatus for transmitting longhand characters<\/strong> is more complicated\nthan that just described. Two telephones are now used, and the punched\ntape has in it five rows of perforations.<\/phrase>","copy<\/word>","examine<\/word>","trace<\/word>","combined horizontal<\/word>","vertical movements<\/word>","If we take a copy<\/strong>-book<\/strong> and examine<\/strong> the letters, we shall see that they\nall occupy one, two, or three bands of space. For instance, _a_,\nbetween the lines, occupies one band; _g_, two bands; and _f_, three.\nIn forming letters, the movements of the fingers trace<\/strong> curves and\nstraight lines<\/strong>, the curves being the resultants of combined horizontal<\/strong>\nand vertical movements<\/strong>.<\/phrase>","order<\/word>","add<\/word>","second telephone<\/word>","metal bar<\/word>","Messrs. Pollak and Virag, in order<\/strong> to produce<\/strong> curves, were obliged to\nadd<\/strong> a second telephone<\/strong>, furnished also with a metal bar<\/strong> joined to the\nmirror, which rests on three points instead of on two. One of these\npoints is fixed, the other two represent the ends of the two diaphragm\nbars, which move<\/strong> the mirror vertically and horizontally respectively,\neither separately or simultaneously.<\/phrase>","punched paper<\/word>","cross strokes<\/word>","composite movement<\/word>","curve results<\/word>","A word about the punched paper<\/strong> before going further. It contains, as\nwe have said, five rows of perforations. The top three of these are\nconcerned only with the up-and-down strokes<\/strong> of the letters, the bottom\ntwo with the cross strokes<\/strong>. When a hole of one set is acting in unison\nwith a hole of the other set a composite movement<\/strong> or curve results<\/strong>.<\/phrase>","topmost row<\/word>","known strength<\/word>","return strokes<\/word>","upper part<\/word>","equal strength<\/word>","centre zone<\/word>","positive currents<\/word>","vertical strokes<\/word>","lower zones<\/word>","stroke<\/word>","The topmost row<\/strong> of all sends through the wires a negative current of\nknown strength<\/strong>; this produces upward and return strokes<\/strong> in the upper\nzone of the letters: for instance, the upper part<\/strong> of a _t_. The second\nrow passes _positive_ currents of equal strength<\/strong> with the negative,\nand influences the up-and-down strokes<\/strong> of the centre zone<\/strong>, _e.g._\nthose of _o_; the third row passes positive currents<\/strong> _twice_ as strong\nas the negative, and is responsible for double<\/strong>-length vertical strokes<\/strong>\nin the centre and lower zones<\/strong>, _e.g._ the stroke<\/strong> in _p_.<\/phrase>","vertical elements<\/word>","same path<\/word>","counteracting tendency<\/word>","light point<\/word>","other times<\/word>","horizontal movements<\/word>","balance<\/word>","right-to-left element<\/word>","left curve<\/word>","second telephone diaphragm<\/word>","vertical axis<\/word>","In order<\/strong> that the record<\/strong> shall not be a series of zigzags it is\nnecessary that the return strokes<\/strong> in the vertical elements<\/strong> shall be on\nthe same path<\/strong> as the out strokes; and as the point<\/strong> of light<\/strong> is\ncontinuously tending to move<\/strong> from left to right of the paper there\nmust at times be present<\/strong> a counteracting tendency<\/strong> counterbalancing it\nexactly, so that the path of the light point<\/strong> is purely vertical. At\nother times<\/strong> not merely must the horizontal movements<\/strong> balance<\/strong> each\nother, but the right-to-left element<\/strong> must be stronger than the\nleft-to-right, so that strokes such as the left curve<\/strong> of an _e_ may be\npossible. To this end<\/strong> rows 4 and 5 of the perforations pass<\/strong> currents\nworking the second telephone diaphragm<\/strong>, which moves the mirror on a\nvertical axis<\/strong> so that it reflects the ray horizontally.<\/phrase>","permit<\/word>","different length<\/word>","little junction-hooks<\/word>","such letters<\/word>","It will be noticed that the holes in rows 3, 4, 5 vary in size to\npermit<\/strong> the passage of currents during periods of different length<\/strong>. In\nthis manner the little junction-hooks<\/strong> of such letters<\/strong> as _r_, _w_,\n_v_, _b_ are effected.<\/phrase>","sensitised paper strip<\/word>","chemical baths<\/word>","As fast as the sensitised paper strip<\/strong> is covered with the movements of\nthe dancing spot<\/strong> of light<\/strong> it is passed on over rollers through\ndeveloping and fixing chemical baths<\/strong>; so that the receiving of\nmessages is purely automatic.<\/phrase>","judge<\/word>","ingenious system<\/word>","short section<\/word>","The reader can judge<\/strong> for himself the results of this ingenious system<\/strong>\nas shown in a short section<\/strong> of a message transmitted by Mr. Pollak.\nThe words shown actually occupied two seconds in transmission. They\nare beautifully clear<\/strong>.<\/phrase>","device thirty sets<\/word>","small calculation<\/word>","arrive<\/word>","interesting figures<\/word>","united output<\/word>","It is said that by the aid of a special \"multiplex\" device thirty sets<\/strong>\nof Pollak-Virag<\/strong> apparatus can be used simultaneously on a line! 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