The Romance of Modern Invention Part 1

The Romance of Modern Invention.

by Archibald Williams.

WIRELESS TELEGRAPHY

One day in 1845 a man named Tawell, dressed as a Quaker, stepped into a train at Slough Station on the Great Western Railway, and travelled to London. When he arrived in London the innocent-looking Quaker was arrested, much to his amazement and dismay, on the charge of having committed a foul murder in the neighbourhood of Slough. The news of the murder and a description of the murderer had been telegraphed from that place to Paddington, where a detective met the train and shadowed the miscreant until a convenient opportunity for arresting him occurred. Tawell was tried, condemned, and hung, and the public for the first time generally realised the power for good dormant in the as yet little developed electric telegraph.

Thirteen years later two vessels met in mid-Atlantic laden with cables which they joined and paid out in opposite directions, till Ireland and Newfoundland were reached. The first electric message pa.s.sed on August 7th of that year from the New World to the Old. The telegraph had now become a world-power.

The third epoch-making event in its history is of recent date. On December 12, 1901, Guglielmo Marconi, a young Italian, famous all over the world when but twenty-two years old, suddenly sprang into yet greater fame. At Hospital Point, Newfoundland, he heard by means of a kite, a long wire, a delicate tube full of tiny particles of metal, and a telephone ear-piece, signals transmitted from far-off Cornwall by his colleagues. No wires connected Poldhu, the Cornish station, and Hospital Point. The three short dot signals, which in the Morse code signify the letter S, had been borne from place to place by the limitless, mysterious ether, that strange substance of which we now hear so much, of which wise men declare we know so little.

Marconi's great achievement, which was of immense importance, naturally astonished the world. Of course, there were not wanting those who discredited the report. Others, on the contrary, were seized with panic and showed their readiness to believe that the Atlantic had been spanned aerially, by selling off their shares in cable companies.

To use the language of the money-market, there was a temporary "slump"

in cable shares. The world again woke up--this time to the fact that experiments of which it had heard faintly had at last culminated in a great triumph, marvellous in itself, and yet probably nothing in comparison with the revolution in the transmission of news that it heralded.

The subject of Wireless Telegraphy is so wide that to treat it fully in the compa.s.s of a single chapter is impossible. At the same time it would be equally impossible to pa.s.s it over in a book written with the object of presenting to the reader the latest developments of scientific research. Indeed, the attention that it has justly attracted ent.i.tle it, not merely to a place, but to a leading place; and for this reason these first pages will be devoted to a short account of the history and theory of Wireless Telegraphy, with some mention of the different systems by which signals have been sent through s.p.a.ce.

On casting about for a point at which to begin, the writer is tempted to attack the great topic of the ether, to which experimenters in many branches of science are now devoting more and more attention, hoping to find in it an explanation of and connection between many phenomena which at present are of uncertain origin.

What is Ether? In the first place, its very existence is merely a.s.sumed, like that of the atom and the molecule. n.o.body can say that he has actually seen or had any experience of it. The a.s.sumption that there is such a thing is justified only in so far as that a.s.sumption explains and reconciles phenomena of which we have experience, and enables us to form theories which can be scientifically demonstrated correct. What scientists now say is this: that everything which we see and touch, the air, the infinity of s.p.a.ce itself, is permeated by a _something_, so subtle that, no matter how continuous a thing may seem, it is but a concourse of atoms separated by this something, the Ether. Reasoning drove them to this conclusion.

It is obvious that an effect cannot come out of nothing. Put a clock under a bell-gla.s.s and you hear the ticking. Pump out the air and the ticking becomes inaudible. What is now not in the gla.s.s that was there before? The air. Reason, therefore, obliges us to conclude that air is the means whereby the ticking is audible to us. No air, no sound.

Next, put a lighted candle on the further side of the exhausted bell-gla.s.s. We can see it clearly enough. The absence of air does not affect light. But can we believe that there is an absolute gap between us and the light? No! It is far easier to believe that the bell-gla.s.s is as full as the outside atmosphere of the something that communicates the sensation of light from the candle to the eye. Again, suppose we measure a bar of iron very carefully while cold and then heat it. We shall find that it has expanded a little. The iron atoms, we say, have become more energetic than before, repel each other and stand further apart. What then is in the intervening s.p.a.ces? Not air, which cannot be forced through iron whether hot or cold. No! the ether: which pa.s.ses easily through crevices so small as to bar the way to the atoms of air.

[Ill.u.s.tration: _A Corner of M. Marconi's cabin on board S.S.

"Minneapolis," showing instruments used in Wireless Telegraphy._]

Once more, suppose that to one end of our iron bar we apply the negative "pole" of an electric battery, and to the other end the positive pole. We see that a current pa.s.ses through the bar, whether hot or cold, which implies that it jumps across all the ether gaps, or rather is conveyed by them from one atom to another.

The conclusion then is that ether is not merely omnipresent, penetrating all things, but the medium whereby heat, light, electricity, perhaps even thought itself, are transmitted from one point to another.

In what manner is the transmission effected? We cannot imagine the ether behaving in a way void of all system.

The answer is, by a wave motion. The ether must be regarded as a very elastic solid. The agitation of a portion of it by what we call heat, light, or electricity, sets in motion adjoining particles, until they are moving from side to side, but not forwards; the resultant movement resembling that of a snake tethered by the tail.

These ether waves vary immensely in length. Their qualities and effects upon our bodies or sensitive instruments depend upon their length. By means of ingenious apparatus the lengths of various waves have been measured. When the waves number 500 billion per second, and are but the 40,000th of an inch long they affect our eyes and are named light--red light. At double the number and half the length, they give us the sensation of violet light.

When the number increases and the waves shorten further, our bodies are "blind" to them; we have no sense to detect their presence.

Similarly, a slower vibration than that of red light is imperceptible until we reach the comparatively slow pace of 100 vibrations per second, when we become aware of heat.

Ether waves may be compared to the notes on a piano, of which we are acquainted with some octaves only. The gaps, the unknown octaves, are being discovered slowly but surely. Thus, for example, the famous X-rays have been a.s.signed to the topmost octave; electric waves to the notes between light and heat. Forty years ago Professor Clerk Maxwell suggested that light and electricity were very closely connected, probably differing only in their wave-length. His theory has been justified by subsequent research. The velocity of light (185,000 miles per second) and that of electric currents have been proved identical.

Hertz, a professor in the university of Bonn, also showed (1887-1889) that the phenomena of light--reflection, refraction, and concentration of rays--can be repeated with electric currents.

We therefore take the word of scientists that the origin of the phenomena called light and electricity is the same--vibration of ether. It at once occurs to the reader that their behaviour is so different that they might as well be considered of altogether different natures.

For instance, interpose the very thinnest sheet of metal between a candle and the eye, and the light is cut off. But the sheet will very readily convey electricity. On the contrary, gla.s.s, a substance that repels electricity, is transparent, _i.e._ gives pa.s.sage to light. And again, electricity can be conveyed round as many corners as you please, whereas light will travel in straight lines only.

To clear away our doubts we have only to take the lighted candle and again hold up the metal screen. Light does not pa.s.s through, but heat does. Subst.i.tute for the metal a very thin tank filled with a solution of alum, and then light pa.s.ses, but heat is cut off. So that heat and electricity _both_ penetrate what is impenetrable to light; while light forces a pa.s.sage securely barred against both electricity and heat. And we must remember that open s.p.a.ce conveys all alike from the sun to the earth.

On meeting what we call solid matter, ether waves are influenced, not because ether is wanting in the solid matter, but because the presence of something else than ether affects the intervening ether itself.

Consequently gla.s.s, to take an instance, so affects ether that a very rapid succession of waves (light) are able to continue their way through its interstices, whereas long electric waves are so hampered that they die out altogether. Metal on the other hand welcomes slow vibrations (_i.e._ long waves), but speedily kills the rapid shakes of light. In other words, _transparency_ is not confined to light alone.

All bodies are transparent to some variety of rays, and many bodies to several varieties. It may perhaps even be proved that there is no such thing as absolute resistance, and that our inability to detect penetration is due to lack of sufficiently delicate instruments.

The cardinal points to be remembered are these:--

That the ether is a universal medium, conveying all kinds and forms of energy.

That these forms of energy differ only in their rates of vibration.

That the rate of vibration determines what power of penetration the waves shall have through any given substance.

Now, it is generally true that whereas matter of any kind offers resistance to light--that is, is not so perfect a conductor as the ether--many substances, especially metals, are more sensitive than ether to heat and electricity. How quickly a spoon inserted into a hot cup of tea becomes uncomfortably hot, though the hand can be held very close to the liquid without feeling more than a gentle warmth. And we all have noticed that the very least air-gap in an electric circuit effectively breaks a current capable of traversing miles of wire. If the current is so intense that it insists on pa.s.sing the gap, it leaps across with a report, making a spark that is at once intensely bright and hot. Metal wires are to electricity what speaking tubes are to sound; they are as it were electrical tubes through the air and ether.

But just as a person listening outside a speaking tube might faintly hear the sounds pa.s.sing through it, so an instrument gifted with an "electric ear" would detect the currents pa.s.sing through the wire.

Wireless telegraphy is possible because mankind has discovered instruments which act as _electric ears or eyes_, catching and recording vibrations that had hitherto remained undetected.

The earliest known form of wireless telegraphy is transmission of messages by light. A man on a hill lights a lamp or a fire. This represents his instrument for agitating the ether into waves, which proceed straight ahead with incredible velocity until they reach the receiver, the eye of a man watching at a point from which the light is visible.

Then came electric telegraphy.

At first a complete circuit (two wires) was used. But in 1838 it was discovered that if instead of two wires only one was used, the other being replaced by an earth connection, not only was the effect equally powerful, but even double of what it was with the metallic circuit.

Thus the first step had been taken towards wireless electrical telegraphy.

The second was, of course, to abolish the other wire.

This was first effected by Professor Morse, who, in 1842, sent signals across the Susquehanna River without metallic connections of any sort.

Along each bank of the river was stretched a wire three times as long as the river was broad. In the one wire a battery and transmitter were inserted, in the other a receiving instrument or galvanometer. Each wire terminated at each end in a large copper plate sunk in the water.

Morse's conclusions were that provided the wires were long enough and the plates large enough messages could be transmitted for an indefinite distance; the current pa.s.sing from plate to plate, though a large portion of it would be lost in the water.[1]

[1] It is here proper to observe that the term _wireless_ telegraphy, as applied to electrical systems, is misleading, since it implies the absence of wires; whereas in all systems wires are used. But since it is generally understood that by wireless telegraphy is meant telegraphy without _metal connections_, and because the more improved methods lessen more and more the amount of wire used, the phrase has been allowed to stand.

About the same date a Scotchman, James Bowman Lindsay of Dundee, a man as rich in intellectual attainments as he was pecuniarily poor, sent signals in a similar manner across the River Tay. In September, 1859, Lindsay read a paper before the British a.s.sociation at Dundee, in which he maintained that his experiments and calculations a.s.sured him that by running wires along the coasts of America and Great Britain, by using a battery having an acting surface of 130 square feet and immersed sheets of 3000 square feet, and a coil weighing 300 lbs., he could send messages from Britain to America. Want of money prevented the poor scholar of Dundee from carrying out his experiments on a large enough scale to obtain public support. He died in 1862, leaving behind him the reputation of a man who in the face of the greatest difficulties made extraordinary electrical discoveries at the cost of unceasing labour; and this in spite of the fact that he had undertaken and partly executed a gigantic dictionary in fifty different languages!

[Ill.u.s.tration: _M. Marconi's Travelling Station for Wireless Telegraphy._]

The transmission of electrical signals through matter, metal, earth, or water, is effected by _conduction_, or the _leading_ of the currents in a circuit. When we come to deal with aerial transmission, _i.e._ where one or both wires are replaced by the ether, then two methods are possible, those of _induction_ and Hertzian waves.

To take the induction method first. Whenever a current is sent through a wire magnetism is set up in the ether surrounding the wire, which becomes the core of a "magnetic field." The magnetic waves extend for an indefinite distance on all sides, and on meeting a wire _parallel_ to the electrified wire _induce_ in it a _dynamical_ current similar to that which caused them. Wherever electricity is present there is magnetism also, and _vice versa_. Electricity--produces magnetism--produces electricity. The invention of the Bell telephone enabled telegraphers to take advantage of this law.

In 1885 Sir William Preece, now consulting electrical engineer to the General Post-Office, erected near Newcastle two insulated squares of wire, each side 440 yards long. The squares were horizontal, parallel, and a quarter of a mile apart. On currents being sent through the one, currents were detected in the other by means of a telephone, which remained active even when the squares were separated by 1000 yards.

Sir William Preece thus demonstrated that signals could be sent without even an earth connection, _i.e._ entirely through the ether.

In 1886 he sent signals between two parallel telegraph wires 4-1/2 miles apart. And in 1892 established a regular communication between Flatholm, an island fort in the Bristol Channel, and Lavernock, a point on the Welsh coast 3-1/3 miles distant.

The inductive method might have attained to greater successes had not a formidable rival appeared in the Hertzian waves.

In 1887 Professor Hertz discovered that if the discharge from a Leyden jar were pa.s.sed through wires containing an air-gap across which the discharge had to pa.s.s, sparks would also pa.s.s across a gap in an almost complete circle or square of wire held at some distance from the jar. This "electric eye," or detector, could have its gap so regulated by means of a screw that at a certain width its effect would be most p.r.o.nounced, under which condition the detector, or receiver, was "in tune" with the exciter, or transmitter. Hertz thus established three great facts, that--