The Romance of Modern Invention- Excerpts
Archibald Williams
Rita Head's Group
The Romance of Modern Invention
by Archibald WilliamsWIRELESS TELEGRAPHYOne 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 passed 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 aërially, 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 compass of a single chapter is impossible. At the same time it
would be equally impossible to pass 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 entitle 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 space.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
assumed, like that of the atom and the molecule. Nobody can say that
he has actually seen or had any experience of it. The assumption that
there is such a thing is justified only in so far as that assumption
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 space 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-glass and you hear the ticking. Pump out the air and the
ticking becomes inaudible. What is now not in the glass 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-glass. 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-glass
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 spaces? Not air,
which cannot be forced through iron whether hot or cold. No! the
ether: which passes easily through crevices so small as to bar the way
to the atoms of air.[Illustration: _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 passes 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 assigned 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, glass, a substance that
repels electricity, is transparent, _i.e._ gives passage 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 pass through, but heat
does. Substitute for the metal a very thin tank filled with a solution
of alum, and then light passes, but heat is cut off. So that heat and
electricity _both_ penetrate what is impenetrable to light; while
light forces a passage securely barred against both electricity and
heat. And we must remember that open space 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 glass, 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 passing 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 passing through it, so an instrument gifted with an
"electric ear" would detect the currents passing 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 passing 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 Association at Dundee, in
which he maintained that his experiments and calculations assured 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![Illustration: _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 aërial 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 versâ_. 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 passed through wires containing an air-gap across which the
discharge had to pass, sparks would also pass 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 pronounced, under which condition the detector, or receiver,
was "in tune" with the exciter, or transmitter. Hertz thus established
three great facts, that-- (_a_) A discharge of static (_i.e._ collected) electricity
across an air-gap produced strong electric waves in the ether
on all sides. (_b_) That these waves could be _caught_. (_c_) That under certain conditions the catcher worked most
effectively.Out of these three discoveries has sprung the latest phase of wireless
telegraphy, as exploited by Signor Marconi. He, in common with
Professors Branly of Paris, Popoff of Cronstadt, and Slaby of
Charlottenburg, besides many others, have devoted their attention to
the production of improved means of sending and receiving the Hertzian
waves. Their experiments have shown that two things are required in
wireless telegraphy-- (i.) That the waves shall have great penetrating power, so as
to pierce any obstacle. (ii.) That they shall retain their energy, so that a _maximum_
of their original force shall reach the receiver.The first condition is fulfilled best by waves of great length; the
second by those which, like light, are of greatest frequency. For best
telegraphic results a compromise must be effected between these
extremes, neither the thousand-mile long waves of an alternating
dynamo nor the light waves of many thousands to an inch being of use.
The Hertzian waves are estimated to be 230,000,000 per second; at
which rate they would be 1-1/2 yards long. They vary considerably,
however, on both sides of this rate and dimension.Marconi's transmitter consists of three parts--a battery; an induction
coil, terminating in a pair of brass balls, one on each side of the
air-gap; and a Morse transmitting-key. Upon the key being depressed, a
current from the battery passes through the coil and accumulates
electricity on the brass balls until its tension causes it to leap
from one to the other many millions of times in what is called a
spark. The longer the air-gap the greater must be the accumulation
before the leap takes place, and the greater the power of the
vibrations set up. Marconi found that by connecting a kite or balloon
covered with tinfoil by an aluminium wire with one of the balls, the
effect of the waves was greatly increased. Sometimes he replaced the
kite or balloon by a conductor placed on poles two or three hundred
feet high, or by the mast of a ship.We now turn to the receiver.In 1879 Professor D. E. Hughes observed that a microphone, in
connection with a telephone, produced sounds in the latter even when
the microphone was at a distance of several feet from coils through
which a current was passing. A microphone, it may be explained, is in
its simplest form a loose connection in an electric circuit, which
causes the current to flow in fits and starts at very frequent
intervals. He discovered that a metal microphone stuck, or cohered,
after a wave had influenced it, but that a carbon microphone was
self-restoring, _i.e._ regained its former position of loose contact
as soon as a wave effect had ceased.In 1891 Professor Branly of Paris produced a "coherer," which was
nothing more than a microphone under another name. Five years later
Marconi somewhat altered Branly's contrivance, and took out a patent
for a coherer of his own.It is a tiny glass tube, about two inches long and a tenth of an inch
in diameter inside. A wire enters it at each end, the wires
terminating in two silver plugs fitting the bore of the tube. A space
of 1/32 inch is left between the plugs, and this space is filled with
special filings, a mixture of 96 parts of nickel to 4 of silver, and
the merest trace of mercury. The tube is exhausted of almost all its
air before being sealed.This little gap filled with filings is, except when struck by an
electric wave, to all practical purposes a non-conductor of
electricity. The metal particles touch each other so lightly that they
offer great resistance to a current.But when a Hertzian wave flying through the ether strikes the coherer,
the particles suddenly press hard on one another, and make a bridge
through which a current can pass. The current works a "relay," or
circuit through which a stronger current passes, opening and closing
it as often as the coherer is influenced by a wave. The relay actuates
a tapper that gently taps the tube after each wave-influence, causing
the particles to _de_cohere in readiness for the succeeding wave, and
also a Morse instrument for recording words in dots and dashes on a
long paper tape.The coherer may be said to resemble an engine-driver, and the "relay"
an engine. The driver is not sufficiently strong to himself move a
train, but he has strength enough to turn on steam and make the engine
do the work. The coherer is not suitable for use with currents of the
intensity required to move a Morse recorder, but it easily switches a
powerful current into another circuit.Want of space forbids a detailed account of Marconi's successes with
his improved instruments, but the appended list will serve to show
how he gradually increased the distance over which he sent signals
through space.In 1896 he came to England. That year he signalled from a room in the
General Post-Office to a station on the roof 100 yards distant.
Shortly afterwards he covered 2 miles on Salisbury Plain.In May, 1897, he sent signals from Lavernock Point to Flatholm, 3-1/3
miles. This success occurred at a critical time, for Sir W. Preece had
already, as we have seen, bridged the same gap by his induction
method, and for three days Marconi failed to accomplish the feat with
his apparatus, so that it appeared as though the newer system were the
less effective of the two. But by carrying the transmitting instrument
on to the beach below the cliff on which it had been standing, and
joining it by a wire to the pole already erected on the top of the
cliff, Mr. Marconi, thanks to a happy inspiration, did just what was
needed; he got a greater length of wire to send off his waves from.
Communication was at once established with Flatholm, and on the next
day with Brean Down, on the other side of the Bristol Channel, and
8-2/3 miles distant. Then we have-- Needles Hotel to Swanage 17-1/2 miles.
Salisbury to Bath 34 "
French Coast to Harwich 90 "
Isle of Wight to The Lizard 196 "
At Sea (1901) 350 "
Dec. 17, 1901, England to America 2099 "[Illustration: _Poldhu Towers, the Station put down by the Marconi
Wireless Telegraph Company, Limited, for carrying on a system of
transatlantic wireless telegraphy between England and America. From
the four towers are suspended the ærial wires which are carried into
the buildings in the centre. The towers are 215 feet in height, and
are made of wood._]A more pronounced, though perhaps less sensational, success than even
this last occurred at the end of February, 1902. Mr. Marconi, during a
voyage to America on the s.s. _Philadelphia_ remained in communication
with Poldhu, Cornwall, until the vessel was 1550 miles distant,
receiving messages on a Morse recorder for any one acquainted with the
code to read. Signals arrived for a further 500 miles, but owing to
his instruments not being of sufficient strength, Mr. Marconi could
not reply.When the transatlantic achievement was announced at the end of 1901,
there was a tendency in some quarters to decry the whole system. The
critics laid their fingers on two weak points.In the first place, they said, the speed at which the messages could
be transmitted was too slow to insure that the system would pay. Mr.
Marconi replied that there had been a time when one word per minute
was considered a good working rate across the Atlantic cable; whereas
he had already sent twenty-two words per minute over very long
distances. A further increase of speed was only a matter of time.The second objection raised centred on the lack of secrecy resulting
from signals being let loose into space to strike any instrument
within their range; and also on the confusion that must arise when the
ether was traversed by many sets of electric waves.The young Italian inventor had been throughout his experiments aware
of these defects and sought means to remedy them. In his earliest
attempts we find him using parabolic metal screens to project his
waves in any required direction and prevent their going in any other.
He also employed strips of metal in conjunction with the coherer, the
strips or "wings" being of such a size as to respond most readily to
waves of a certain length.The electric oscillations coming from the aerial wires carried on
poles, kites, &c., were of great power, but their energy dispersed
very quickly into space in a series of rapidly diminishing vibrations.
This fact made them affect to a greater or less degree any receiver
they might encounter on their wanderings. If you go into a room where
there is a piano and make a loud noise near the instrument a jangle of
notes results. But if you take a tuning-fork and after striking it
place it near the strings, only one string will respond, _i.e._ that
of the same pitch as the fork.What is required in wireless telegraphy is a system corresponding to
the use of the tuning-fork. Unfortunately, it has been discovered that
the syntony or tuning of transmitter and receiver reduces the distance
over which they are effective. An electric "noise" is more
far-reaching than an electric "note."Mr. Marconi has, however, made considerable advances towards combining
the sympathy and secrecy of the tuning system with the power of the
"noise" system. By means of delicately adjusted "wings" and coils he
has brought it about that a series of waves having small individual
strength, but great regularity, shall produce on the receiver a
_cumulative_ effect, storing, as it were, electricity on the surface
of the receiver "wings" until it is of sufficient power to overcome
the resistance of the coherer.That tuned wireless telegraphy is, over moderate distances, at least
as secret as that through wires (which can be tapped by induction) is
evident from the fact that during the America Cup Yacht Races Mr.
Marconi sent daily to the _New York Herald_ messages of 4000 total
words, and kept them private in spite of all efforts to intercept
them. He claims to have as many as 250 "tunes"; and, indeed, there
seems to be no limit to their number, so that the would-be "tapper" is
in the position of a man trying to open a letter-lock of which he does
not know the cipher-word. He _may_ discover the right tune, but the
chances are greatly against him. We may be certain that the rapid
advance in wireless telegraphy will not proceed much further before
syntonic messages can be transmitted over hundreds if not thousands of
miles.It is hardly necessary to dwell upon the great prospect that the new
telegraphy opens to mankind. The advantages arising out of a ready
means of communication, freed from the shackles of expensive
connecting wires and cables are, in the main, obvious enough. We have
only to imagine all the present network of wires replaced or
supplemented by ether-waves, which will be able to act between points
(_e.g._ ships and ships, ships and land, moving and fixed objects
generally) which cannot be connected by metallic circuits.Already ocean voyages are being shortened as regards the time during
which passengers are out of contact with the doings of the world. The
transatlantic journey has now a newsless period of but three days.
Navies are being fitted out with instruments that may play as
important a part as the big guns themselves in the next naval war. A
great maritime nation like our own should be especially thankful that
the day is not far distant when our great empire will be connected by
invisible electric links that no enemy may discover and cut.The romantic side of wireless telegraphy has been admirably touched in
some words uttered by Professor Ayrton in 1899, after the reading of a
paper by Mr. Marconi before the Institution of Electrical Engineers."If a person wished to call to a friend" (said the Professor), "he
would use a loud electro-magnetic voice, audible only to him who had
the electro-magnetic ear."'Where are you?' he would say."The reply would come--'I am at the bottom of a coal mine,' or
'Crossing the Andes,' or 'In the middle of the Pacific.' Or, perhaps,
in spite of all the calling, no reply would come, and the person would
then know his friend was dead. Let them think of what that meant; of
the calling which went on every day from room to room of a house,
and then imagine that calling extending from pole to pole; not a noisy
babble, but a call audible to him who wanted to hear and absolutely
silent to him who did not."[Illustration: _Guglielmo Marconi._]When will Professor Ayrton's forecast come true? Who can say? Science
is so full of surprises that the ordinary man wonders with a semi-fear
what may be the next development; and wise men like Lord Kelvin humbly
confess that in comparison with what has yet to be learnt about the
mysterious inner workings of Nature their knowledge is but as
ignorance.HIGH-SPEED TELEGRAPHY.The wonderful developments of wireless telegraphy must not make us
forget that some very interesting and startling improvements have been
made in connection with the ordinary wire-circuit method: notably in
the matter of speed.At certain seasons of the year or under special circumstances which
can scarcely be foreseen, a great rush takes place to transmit
messages over the wires connecting important towns. Now, the best
telegraphists can with difficulty keep up a transmitting speed of even
fifty words a minute for so long as half-an-hour. The Morse alphabet
contains on the average three signals for each letter, and the average
length of a word is six letters. Fifty words would therefore contain
between them 900 signals, or fifteen a second. The strain of sending
or noting so many for even a brief period is very wearisome to the
operator.Means have been found of replacing the telegraph clerk, so far as the
actual signalling is concerned, by mechanical devices.In 1842 Alexander Bain, a watchmaker of Thurso, produced what is known
as a "chemical telegraph." The words to be transmitted were set up in
large metal type, all capitals, connected with the positive pole of
a battery, the negative pole of which was connected to earth. A metal
brush, divided into five points, each terminating a wire, was passed
over the metal type. As often as a division of the brush touched metal
it completed the electric circuit in the wire to which it was joined,
and sent a current to the receiving station, where a similar brush was
passing at similar speed over a strip of paper soaked in iodide of
potassium. The action of the electricity decomposed the solution,
turning it blue or violet. The result was a series of letters divided
longitudinally into five belts separated by white spaces representing
the intervals between the contact points of the brush.[Illustration: _The receiving instrument used by Messrs. Pollak &
Virag in their high-speed system of telegraphy. This instrument is
capable of receiving and photographically recording messages at the
astonishing speed of 50,000 words an hour._]The Bain Chemical Telegraph was able to transmit the enormous number
of 1500 words per minute; that is, at ten times the rate of ordinary
conversation! But even when improvements had reduced the line wires
from five to one, the system, on account of the method of composing
the message to be sent, was not found sufficiently practical to come
into general use.Its place was taken by slower but preferable systems: those of duplex
and multiplex telegraphy.When a message is sent over the wires, the actual time of making the
signals is more than is required for the current to pass from place to
place. This fact has been utilised by the inventors of methods whereby
two or more messages may not only be sent the _same_ way along the
same wire, but may also be sent in _different_ directions. Messages
are "duplex" when they travel across one another, "multiplex" when
they travel together.The principle whereby several instruments are able to use the same
wire is that of _distributing_ among the instruments the time during
which they are in contact with the line.Let us suppose that four transmitters are sending messages
simultaneously from London to Edinburgh.Wires from all four instruments are led into a circular contact-maker,
divided into some hundreds of insulated segments connected in rotation
with the four transmitters. Thus instrument A will be joined to
segments 1, 5, 9, 13; instrument B to segments 2, 6, 10, 14;
instrument C with segments 3, 7, 11, 15; and so on.Along the top of the segments an arm, connected with the telegraph
line to Edinburgh, revolves at a uniform rate. For about 1/500 of a
second it unites a segment with an instrument. If there are 150
segments on the "distributor," and the arm revolves three times a
second, each instrument will be put into contact with the line rather
oftener than 110 times per second. And if the top speed of fifty words
a minute is being worked to, each of the fifteen signals occurring in
each second will be on the average divided among seven moments of
contact.A similar apparatus at Edinburgh receives the messages. It is evident
that for the system to work satisfactorily, or even to escape dire
confusion, the revolving arms must run at a level speed in perfect
unison with one another. When the London arm is over segment 1, the
Edinburgh arm must cover the same number. The greatest difficulty in
multiplex telegraphy has been to adjust the timing exactly.Paul la Cour of Copenhagen invented for driving the arms a device
called the Phonic Wheel, as its action was regulated by the vibrations
of a tuning-fork. The wheel, made of soft iron, and toothed on its
circumference, revolves at a short distance from the pole of a magnet.
As often as a current enters the magnet the latter attracts the
nearest tooth of the wheel; and if a regular series of currents pass
through it the motion of the wheel will be uniform. M. la Cour
produced the regularity of current impulses in the motor magnet by
means of a tuning-fork, which is unable to vibrate more than a certain
number of times a second, and at each vibration closed a circuit
sending current into the magnet. To get two tuning-forks of the same
note is an easy matter; and consequently a uniformity of rotation at
both London and Edinburgh stations may be insured.So sensitive is this "interrupter" system that as many as sixteen
messages can be sent simultaneously, which means that a single wire is
conveying from 500 to 800 words a minute. We can easily understand the
huge saving that results from such a system; the cost of instruments,
interrupter, &c., being but small in proportion to that of a number
of separate conductors.The word-sending capacity of a line may be even further increased by
the use of automatic transmitters able to work much faster in
signal-making than the human brain and hand. Sir Charles Wheatstone's
Automatic Transmitter has long been used in the Post-Office
establishments.The messages to be sent are first of all punched on a long tape with
three parallel rows of perforations. The central row is merely for
guiding the tape through the transmitting machine. The positions of
the holes in the two outside rows relatively to each other determine
the character of the signal to be sent. Thus, when three holes
(including the central one) are abreast, a Morse "dot" is signified;
when the left-hand hole is one place behind the right hand, a "dash"
will be telegraphed.In the case of a long communication the matter is divided among a
number of clerks operating punching machines. Half-a-dozen operators
could between them punch holes representing 250 to 300 words a minute;
and the transmitter is capable of despatching as many in the same
time, while it has the additional advantage of being tireless.The action of the transmitter is based upon the reversal of the
direction or nature of current. The punched tape is passed between an
oscillating lever, carrying two points, and plates connected with the
two poles of the battery. As soon as a hole comes under a pin the pin
drops through and makes a contact.At the receiving end the wire is connected with a coil wound round the
pole of a permanent bar-magnet. Such a magnet has what is known as a
north pole and a south pole, the one attractive and the other
repulsive of steel or soft iron. Any bar of soft iron can be made
temporarily into a magnet by twisting round it a few turns of a wire
in circuit with the poles of a battery. But which will be the north
and which the south pole depends on the _direction_ of the current.
If, then, a current passes in one direction round the north pole of a
permanent magnet it will increase the magnet's attractive power, but
will decrease it if sent in the other direction.The "dot" holes punched in the tape being abreast cause first a
positive and then a negative current following at a very short
interval; but the "dash" holes not being opposite allow the positive
current to occupy the wires for a longer period. Consequently the
Morse marker rests for correspondingly unequal periods on the
recording "tape," giving out a series of dots and dashes, as the inker
is snatched quickly or more leisurely from the paper.The Wheatstone recorder has been worked up to 400 words a minute, and
when two machines are by the multiplex method acting together this
rate is of course doubled.As a speed machine it has, however, been completely put in the shade
by a more recent invention of two Hungarian electricians, Anton Pollak
and Josef Virag, which combines the perforated strip method of
transmission with the telephone and photography. The message is sent
off by means of a punched tape, and is recorded by means of a
telephonic diaphragm and light marking a sensitised paper.In 1898 the inventors made trials of their system for the benefit of
the United Electrical Company of Buda-Pesth. The Hungarian capital was
connected by two double lines of wire with a station 200 miles
distant, where the two sets were joined so as to give a single circuit
of 400 miles in length. A series of tests in all weathers showed that
the Pollak-Virag system could transmit as many as 100,000 words an
hour over that distance.From Hungary the inventors went to the United States, in which country
of "records" no less than 155,000 words were despatched and received
in the sixty minutes. This average--2580 words per minute, 43 per
second--is truly remarkable! Even between New York and Chicago,
separated by 950 odd miles, the wires kept up an average of 1000 per
minute.The apparatus that produces these marvellous results is of two types.
The one type records messages in the Morse alphabet, the other makes
clearly-written longhand characters. The former is the faster of the
two, but the legibility of the other more than compensates for the
decrease of speed by one-half.[Illustration: _Specimens of the punched tape used for transmitting
messages by the Pollak-Virag system, and of a message as it is
delivered by the receiving machine._]The Morse alphabet method closely resembles the Wheatstone system. The
message is prepared for transmission by being punched on a tape. But
there is this difference in the position of the holes, that whereas in
the Wheatstone method two holes are used for each dot and dash, only
one is required in the Pollak-Virag. If to the right of the central
guiding line it signifies a "dash," if to the left, a "dot."The "reversal-of-current" method, already explained, causes at the
receiver end an increase or decrease in the power of a permanent
magnet to attract or repel a diaphragm, the centre of which is
connected by a very fine metal bar with the centre of a tiny mirror
hinged at one side on two points. A very slight movement of the
diaphragm produces an exaggerated movement of the mirror, which, as it
tilts backwards and forwards, reflects the light from an electric lamp
on to a lens, which concentrates the rays into a bright spot, and
focuses them on to a surface of sensitised paper.In their earliest apparatus the inventors attached the paper to the
circumference of a vertical cylinder, which revolved at an even pace
on an axle, furnished at the lower end with a screw thread, so that
the portion of paper affected by the light occupied a spiral path from
top to bottom of the cylinder.In a later edition, however, an endless band of sensitised paper is
employed, and the lamp is screened from the mirror by a horizontal
mantle in which is cut a helical slit making one complete turn of the
cylinder in its length. The mantle is rotated in unison with the
machinery driving the sensitised band; and as it revolves, the spot at
which the light from the filament can pass through the slit to the
mirror is constantly shifting from right to left, and the point at
which the reflected light from the mirror strikes the sensitised paper
from left to right. At the moment when a line is finished, the right
extremity of the mantle begins to pass light again, and the bright
spot of light recommences its work at the left edge of the band, which
has now moved on a space.The movements of the mirror backwards and forwards produce on the
paper a zigzag tracing known as syphon-writing. The record, which is
continuous from side to side of the band, is a series of zigzag
up-and-down strokes, corresponding to the dots and dashes of the Morse
alphabet.The apparatus for transmitting longhand characters is more complicated
than that just described. Two telephones are now used, and the punched
tape has in it five rows of perforations.If we take a copy-book and examine the letters, we shall see that they
all occupy one, two, or three bands of space. For instance, _a_,
between the lines, occupies one band; _g_, two bands; and _f_, three.
In forming letters, the movements of the fingers trace curves and
straight lines, the curves being the resultants of combined horizontal
and vertical movements.Messrs. Pollak and Virag, in order to produce curves, were obliged to
add a second telephone, furnished also with a metal bar joined to the
mirror, which rests on three points instead of on two. One of these
points is fixed, the other two represent the ends of the two diaphragm
bars, which move the mirror vertically and horizontally respectively,
either separately or simultaneously.A word about the punched paper before going further. It contains, as
we have said, five rows of perforations. The top three of these are
concerned only with the up-and-down strokes of the letters, the bottom
two with the cross strokes. When a hole of one set is acting in unison
with a hole of the other set a composite movement or curve results.The topmost row of all sends through the wires a negative current of
known strength; this produces upward and return strokes in the upper
zone of the letters: for instance, the upper part of a _t_. The second
row passes _positive_ currents of equal strength with the negative,
and influences the up-and-down strokes of the centre zone, _e.g._
those of _o_; the third row passes positive currents _twice_ as strong
as the negative, and is responsible for double-length vertical strokes
in the centre and lower zones, _e.g._ the stroke in _p_.In order that the record shall not be a series of zigzags it is
necessary that the return strokes in the vertical elements shall be on
the same path as the out strokes; and as the point of light is
continuously tending to move from left to right of the paper there
must at times be present a counteracting tendency counterbalancing it
exactly, so that the path of the light point is purely vertical. At
other times not merely must the horizontal movements balance each
other, but the right-to-left element must be stronger than the
left-to-right, so that strokes such as the left curve of an _e_ may be
possible. To this end rows 4 and 5 of the perforations pass currents
working the second telephone diaphragm, which moves the mirror on a
vertical axis so that it reflects the ray horizontally.It will be noticed that the holes in rows 3, 4, 5 vary in size to
permit the passage of currents during periods of different length. In
this manner the little junction-hooks of such letters as _r_, _w_,
_v_, _b_ are effected.As fast as the sensitised paper strip is covered with the movements of
the dancing spot of light it is passed on over rollers through
developing and fixing chemical baths; so that the receiving of
messages is purely automatic.The reader can judge for himself the results of this ingenious system
as shown in a short section of a message transmitted by Mr. Pollak.
The words shown actually occupied two seconds in transmission. They
are beautifully clear.It is said that by the aid of a special "multiplex" device thirty sets
of Pollak-Virag apparatus can be used simultaneously on a line! The
reader will be able, by the aid of a small calculation, to arrive at
some interesting figures as regards their united output.
by Archibald WilliamsWIRELESS TELEGRAPHYOne 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 passed 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 aërially, 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 compass of a single chapter is impossible. At the same time it
would be equally impossible to pass 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 entitle 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 space.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
assumed, like that of the atom and the molecule. Nobody can say that
he has actually seen or had any experience of it. The assumption that
there is such a thing is justified only in so far as that assumption
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 space 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-glass and you hear the ticking. Pump out the air and the
ticking becomes inaudible. What is now not in the glass 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-glass. 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-glass
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 spaces? Not air,
which cannot be forced through iron whether hot or cold. No! the
ether: which passes easily through crevices so small as to bar the way
to the atoms of air.[Illustration: _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 passes 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 assigned 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, glass, a substance that
repels electricity, is transparent, _i.e._ gives passage 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 pass through, but heat
does. Substitute for the metal a very thin tank filled with a solution
of alum, and then light passes, but heat is cut off. So that heat and
electricity _both_ penetrate what is impenetrable to light; while
light forces a passage securely barred against both electricity and
heat. And we must remember that open space 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 glass, 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 passing 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 passing through it, so an instrument gifted with an
"electric ear" would detect the currents passing 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 passing 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 Association at Dundee, in
which he maintained that his experiments and calculations assured 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![Illustration: _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 aërial 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 versâ_. 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 passed through wires containing an air-gap across which the
discharge had to pass, sparks would also pass 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 pronounced, under which condition the detector, or receiver,
was "in tune" with the exciter, or transmitter. Hertz thus established
three great facts, that-- (_a_) A discharge of static (_i.e._ collected) electricity
across an air-gap produced strong electric waves in the ether
on all sides. (_b_) That these waves could be _caught_. (_c_) That under certain conditions the catcher worked most
effectively.Out of these three discoveries has sprung the latest phase of wireless
telegraphy, as exploited by Signor Marconi. He, in common with
Professors Branly of Paris, Popoff of Cronstadt, and Slaby of
Charlottenburg, besides many others, have devoted their attention to
the production of improved means of sending and receiving the Hertzian
waves. Their experiments have shown that two things are required in
wireless telegraphy-- (i.) That the waves shall have great penetrating power, so as
to pierce any obstacle. (ii.) That they shall retain their energy, so that a _maximum_
of their original force shall reach the receiver.The first condition is fulfilled best by waves of great length; the
second by those which, like light, are of greatest frequency. For best
telegraphic results a compromise must be effected between these
extremes, neither the thousand-mile long waves of an alternating
dynamo nor the light waves of many thousands to an inch being of use.
The Hertzian waves are estimated to be 230,000,000 per second; at
which rate they would be 1-1/2 yards long. They vary considerably,
however, on both sides of this rate and dimension.Marconi's transmitter consists of three parts--a battery; an induction
coil, terminating in a pair of brass balls, one on each side of the
air-gap; and a Morse transmitting-key. Upon the key being depressed, a
current from the battery passes through the coil and accumulates
electricity on the brass balls until its tension causes it to leap
from one to the other many millions of times in what is called a
spark. The longer the air-gap the greater must be the accumulation
before the leap takes place, and the greater the power of the
vibrations set up. Marconi found that by connecting a kite or balloon
covered with tinfoil by an aluminium wire with one of the balls, the
effect of the waves was greatly increased. Sometimes he replaced the
kite or balloon by a conductor placed on poles two or three hundred
feet high, or by the mast of a ship.We now turn to the receiver.In 1879 Professor D. E. Hughes observed that a microphone, in
connection with a telephone, produced sounds in the latter even when
the microphone was at a distance of several feet from coils through
which a current was passing. A microphone, it may be explained, is in
its simplest form a loose connection in an electric circuit, which
causes the current to flow in fits and starts at very frequent
intervals. He discovered that a metal microphone stuck, or cohered,
after a wave had influenced it, but that a carbon microphone was
self-restoring, _i.e._ regained its former position of loose contact
as soon as a wave effect had ceased.In 1891 Professor Branly of Paris produced a "coherer," which was
nothing more than a microphone under another name. Five years later
Marconi somewhat altered Branly's contrivance, and took out a patent
for a coherer of his own.It is a tiny glass tube, about two inches long and a tenth of an inch
in diameter inside. A wire enters it at each end, the wires
terminating in two silver plugs fitting the bore of the tube. A space
of 1/32 inch is left between the plugs, and this space is filled with
special filings, a mixture of 96 parts of nickel to 4 of silver, and
the merest trace of mercury. The tube is exhausted of almost all its
air before being sealed.This little gap filled with filings is, except when struck by an
electric wave, to all practical purposes a non-conductor of
electricity. The metal particles touch each other so lightly that they
offer great resistance to a current.But when a Hertzian wave flying through the ether strikes the coherer,
the particles suddenly press hard on one another, and make a bridge
through which a current can pass. The current works a "relay," or
circuit through which a stronger current passes, opening and closing
it as often as the coherer is influenced by a wave. The relay actuates
a tapper that gently taps the tube after each wave-influence, causing
the particles to _de_cohere in readiness for the succeeding wave, and
also a Morse instrument for recording words in dots and dashes on a
long paper tape.The coherer may be said to resemble an engine-driver, and the "relay"
an engine. The driver is not sufficiently strong to himself move a
train, but he has strength enough to turn on steam and make the engine
do the work. The coherer is not suitable for use with currents of the
intensity required to move a Morse recorder, but it easily switches a
powerful current into another circuit.Want of space forbids a detailed account of Marconi's successes with
his improved instruments, but the appended list will serve to show
how he gradually increased the distance over which he sent signals
through space.In 1896 he came to England. That year he signalled from a room in the
General Post-Office to a station on the roof 100 yards distant.
Shortly afterwards he covered 2 miles on Salisbury Plain.In May, 1897, he sent signals from Lavernock Point to Flatholm, 3-1/3
miles. This success occurred at a critical time, for Sir W. Preece had
already, as we have seen, bridged the same gap by his induction
method, and for three days Marconi failed to accomplish the feat with
his apparatus, so that it appeared as though the newer system were the
less effective of the two. But by carrying the transmitting instrument
on to the beach below the cliff on which it had been standing, and
joining it by a wire to the pole already erected on the top of the
cliff, Mr. Marconi, thanks to a happy inspiration, did just what was
needed; he got a greater length of wire to send off his waves from.
Communication was at once established with Flatholm, and on the next
day with Brean Down, on the other side of the Bristol Channel, and
8-2/3 miles distant. Then we have-- Needles Hotel to Swanage 17-1/2 miles.
Salisbury to Bath 34 "
French Coast to Harwich 90 "
Isle of Wight to The Lizard 196 "
At Sea (1901) 350 "
Dec. 17, 1901, England to America 2099 "[Illustration: _Poldhu Towers, the Station put down by the Marconi
Wireless Telegraph Company, Limited, for carrying on a system of
transatlantic wireless telegraphy between England and America. From
the four towers are suspended the ærial wires which are carried into
the buildings in the centre. The towers are 215 feet in height, and
are made of wood._]A more pronounced, though perhaps less sensational, success than even
this last occurred at the end of February, 1902. Mr. Marconi, during a
voyage to America on the s.s. _Philadelphia_ remained in communication
with Poldhu, Cornwall, until the vessel was 1550 miles distant,
receiving messages on a Morse recorder for any one acquainted with the
code to read. Signals arrived for a further 500 miles, but owing to
his instruments not being of sufficient strength, Mr. Marconi could
not reply.When the transatlantic achievement was announced at the end of 1901,
there was a tendency in some quarters to decry the whole system. The
critics laid their fingers on two weak points.In the first place, they said, the speed at which the messages could
be transmitted was too slow to insure that the system would pay. Mr.
Marconi replied that there had been a time when one word per minute
was considered a good working rate across the Atlantic cable; whereas
he had already sent twenty-two words per minute over very long
distances. A further increase of speed was only a matter of time.The second objection raised centred on the lack of secrecy resulting
from signals being let loose into space to strike any instrument
within their range; and also on the confusion that must arise when the
ether was traversed by many sets of electric waves.The young Italian inventor had been throughout his experiments aware
of these defects and sought means to remedy them. In his earliest
attempts we find him using parabolic metal screens to project his
waves in any required direction and prevent their going in any other.
He also employed strips of metal in conjunction with the coherer, the
strips or "wings" being of such a size as to respond most readily to
waves of a certain length.The electric oscillations coming from the aerial wires carried on
poles, kites, &c., were of great power, but their energy dispersed
very quickly into space in a series of rapidly diminishing vibrations.
This fact made them affect to a greater or less degree any receiver
they might encounter on their wanderings. If you go into a room where
there is a piano and make a loud noise near the instrument a jangle of
notes results. But if you take a tuning-fork and after striking it
place it near the strings, only one string will respond, _i.e._ that
of the same pitch as the fork.What is required in wireless telegraphy is a system corresponding to
the use of the tuning-fork. Unfortunately, it has been discovered that
the syntony or tuning of transmitter and receiver reduces the distance
over which they are effective. An electric "noise" is more
far-reaching than an electric "note."Mr. Marconi has, however, made considerable advances towards combining
the sympathy and secrecy of the tuning system with the power of the
"noise" system. By means of delicately adjusted "wings" and coils he
has brought it about that a series of waves having small individual
strength, but great regularity, shall produce on the receiver a
_cumulative_ effect, storing, as it were, electricity on the surface
of the receiver "wings" until it is of sufficient power to overcome
the resistance of the coherer.That tuned wireless telegraphy is, over moderate distances, at least
as secret as that through wires (which can be tapped by induction) is
evident from the fact that during the America Cup Yacht Races Mr.
Marconi sent daily to the _New York Herald_ messages of 4000 total
words, and kept them private in spite of all efforts to intercept
them. He claims to have as many as 250 "tunes"; and, indeed, there
seems to be no limit to their number, so that the would-be "tapper" is
in the position of a man trying to open a letter-lock of which he does
not know the cipher-word. He _may_ discover the right tune, but the
chances are greatly against him. We may be certain that the rapid
advance in wireless telegraphy will not proceed much further before
syntonic messages can be transmitted over hundreds if not thousands of
miles.It is hardly necessary to dwell upon the great prospect that the new
telegraphy opens to mankind. The advantages arising out of a ready
means of communication, freed from the shackles of expensive
connecting wires and cables are, in the main, obvious enough. We have
only to imagine all the present network of wires replaced or
supplemented by ether-waves, which will be able to act between points
(_e.g._ ships and ships, ships and land, moving and fixed objects
generally) which cannot be connected by metallic circuits.Already ocean voyages are being shortened as regards the time during
which passengers are out of contact with the doings of the world. The
transatlantic journey has now a newsless period of but three days.
Navies are being fitted out with instruments that may play as
important a part as the big guns themselves in the next naval war. A
great maritime nation like our own should be especially thankful that
the day is not far distant when our great empire will be connected by
invisible electric links that no enemy may discover and cut.The romantic side of wireless telegraphy has been admirably touched in
some words uttered by Professor Ayrton in 1899, after the reading of a
paper by Mr. Marconi before the Institution of Electrical Engineers."If a person wished to call to a friend" (said the Professor), "he
would use a loud electro-magnetic voice, audible only to him who had
the electro-magnetic ear."'Where are you?' he would say."The reply would come--'I am at the bottom of a coal mine,' or
'Crossing the Andes,' or 'In the middle of the Pacific.' Or, perhaps,
in spite of all the calling, no reply would come, and the person would
then know his friend was dead. Let them think of what that meant; of
the calling which went on every day from room to room of a house,
and then imagine that calling extending from pole to pole; not a noisy
babble, but a call audible to him who wanted to hear and absolutely
silent to him who did not."[Illustration: _Guglielmo Marconi._]When will Professor Ayrton's forecast come true? Who can say? Science
is so full of surprises that the ordinary man wonders with a semi-fear
what may be the next development; and wise men like Lord Kelvin humbly
confess that in comparison with what has yet to be learnt about the
mysterious inner workings of Nature their knowledge is but as
ignorance.HIGH-SPEED TELEGRAPHY.The wonderful developments of wireless telegraphy must not make us
forget that some very interesting and startling improvements have been
made in connection with the ordinary wire-circuit method: notably in
the matter of speed.At certain seasons of the year or under special circumstances which
can scarcely be foreseen, a great rush takes place to transmit
messages over the wires connecting important towns. Now, the best
telegraphists can with difficulty keep up a transmitting speed of even
fifty words a minute for so long as half-an-hour. The Morse alphabet
contains on the average three signals for each letter, and the average
length of a word is six letters. Fifty words would therefore contain
between them 900 signals, or fifteen a second. The strain of sending
or noting so many for even a brief period is very wearisome to the
operator.Means have been found of replacing the telegraph clerk, so far as the
actual signalling is concerned, by mechanical devices.In 1842 Alexander Bain, a watchmaker of Thurso, produced what is known
as a "chemical telegraph." The words to be transmitted were set up in
large metal type, all capitals, connected with the positive pole of
a battery, the negative pole of which was connected to earth. A metal
brush, divided into five points, each terminating a wire, was passed
over the metal type. As often as a division of the brush touched metal
it completed the electric circuit in the wire to which it was joined,
and sent a current to the receiving station, where a similar brush was
passing at similar speed over a strip of paper soaked in iodide of
potassium. The action of the electricity decomposed the solution,
turning it blue or violet. The result was a series of letters divided
longitudinally into five belts separated by white spaces representing
the intervals between the contact points of the brush.[Illustration: _The receiving instrument used by Messrs. Pollak &
Virag in their high-speed system of telegraphy. This instrument is
capable of receiving and photographically recording messages at the
astonishing speed of 50,000 words an hour._]The Bain Chemical Telegraph was able to transmit the enormous number
of 1500 words per minute; that is, at ten times the rate of ordinary
conversation! But even when improvements had reduced the line wires
from five to one, the system, on account of the method of composing
the message to be sent, was not found sufficiently practical to come
into general use.Its place was taken by slower but preferable systems: those of duplex
and multiplex telegraphy.When a message is sent over the wires, the actual time of making the
signals is more than is required for the current to pass from place to
place. This fact has been utilised by the inventors of methods whereby
two or more messages may not only be sent the _same_ way along the
same wire, but may also be sent in _different_ directions. Messages
are "duplex" when they travel across one another, "multiplex" when
they travel together.The principle whereby several instruments are able to use the same
wire is that of _distributing_ among the instruments the time during
which they are in contact with the line.Let us suppose that four transmitters are sending messages
simultaneously from London to Edinburgh.Wires from all four instruments are led into a circular contact-maker,
divided into some hundreds of insulated segments connected in rotation
with the four transmitters. Thus instrument A will be joined to
segments 1, 5, 9, 13; instrument B to segments 2, 6, 10, 14;
instrument C with segments 3, 7, 11, 15; and so on.Along the top of the segments an arm, connected with the telegraph
line to Edinburgh, revolves at a uniform rate. For about 1/500 of a
second it unites a segment with an instrument. If there are 150
segments on the "distributor," and the arm revolves three times a
second, each instrument will be put into contact with the line rather
oftener than 110 times per second. And if the top speed of fifty words
a minute is being worked to, each of the fifteen signals occurring in
each second will be on the average divided among seven moments of
contact.A similar apparatus at Edinburgh receives the messages. It is evident
that for the system to work satisfactorily, or even to escape dire
confusion, the revolving arms must run at a level speed in perfect
unison with one another. When the London arm is over segment 1, the
Edinburgh arm must cover the same number. The greatest difficulty in
multiplex telegraphy has been to adjust the timing exactly.Paul la Cour of Copenhagen invented for driving the arms a device
called the Phonic Wheel, as its action was regulated by the vibrations
of a tuning-fork. The wheel, made of soft iron, and toothed on its
circumference, revolves at a short distance from the pole of a magnet.
As often as a current enters the magnet the latter attracts the
nearest tooth of the wheel; and if a regular series of currents pass
through it the motion of the wheel will be uniform. M. la Cour
produced the regularity of current impulses in the motor magnet by
means of a tuning-fork, which is unable to vibrate more than a certain
number of times a second, and at each vibration closed a circuit
sending current into the magnet. To get two tuning-forks of the same
note is an easy matter; and consequently a uniformity of rotation at
both London and Edinburgh stations may be insured.So sensitive is this "interrupter" system that as many as sixteen
messages can be sent simultaneously, which means that a single wire is
conveying from 500 to 800 words a minute. We can easily understand the
huge saving that results from such a system; the cost of instruments,
interrupter, &c., being but small in proportion to that of a number
of separate conductors.The word-sending capacity of a line may be even further increased by
the use of automatic transmitters able to work much faster in
signal-making than the human brain and hand. Sir Charles Wheatstone's
Automatic Transmitter has long been used in the Post-Office
establishments.The messages to be sent are first of all punched on a long tape with
three parallel rows of perforations. The central row is merely for
guiding the tape through the transmitting machine. The positions of
the holes in the two outside rows relatively to each other determine
the character of the signal to be sent. Thus, when three holes
(including the central one) are abreast, a Morse "dot" is signified;
when the left-hand hole is one place behind the right hand, a "dash"
will be telegraphed.In the case of a long communication the matter is divided among a
number of clerks operating punching machines. Half-a-dozen operators
could between them punch holes representing 250 to 300 words a minute;
and the transmitter is capable of despatching as many in the same
time, while it has the additional advantage of being tireless.The action of the transmitter is based upon the reversal of the
direction or nature of current. The punched tape is passed between an
oscillating lever, carrying two points, and plates connected with the
two poles of the battery. As soon as a hole comes under a pin the pin
drops through and makes a contact.At the receiving end the wire is connected with a coil wound round the
pole of a permanent bar-magnet. Such a magnet has what is known as a
north pole and a south pole, the one attractive and the other
repulsive of steel or soft iron. Any bar of soft iron can be made
temporarily into a magnet by twisting round it a few turns of a wire
in circuit with the poles of a battery. But which will be the north
and which the south pole depends on the _direction_ of the current.
If, then, a current passes in one direction round the north pole of a
permanent magnet it will increase the magnet's attractive power, but
will decrease it if sent in the other direction.The "dot" holes punched in the tape being abreast cause first a
positive and then a negative current following at a very short
interval; but the "dash" holes not being opposite allow the positive
current to occupy the wires for a longer period. Consequently the
Morse marker rests for correspondingly unequal periods on the
recording "tape," giving out a series of dots and dashes, as the inker
is snatched quickly or more leisurely from the paper.The Wheatstone recorder has been worked up to 400 words a minute, and
when two machines are by the multiplex method acting together this
rate is of course doubled.As a speed machine it has, however, been completely put in the shade
by a more recent invention of two Hungarian electricians, Anton Pollak
and Josef Virag, which combines the perforated strip method of
transmission with the telephone and photography. The message is sent
off by means of a punched tape, and is recorded by means of a
telephonic diaphragm and light marking a sensitised paper.In 1898 the inventors made trials of their system for the benefit of
the United Electrical Company of Buda-Pesth. The Hungarian capital was
connected by two double lines of wire with a station 200 miles
distant, where the two sets were joined so as to give a single circuit
of 400 miles in length. A series of tests in all weathers showed that
the Pollak-Virag system could transmit as many as 100,000 words an
hour over that distance.From Hungary the inventors went to the United States, in which country
of "records" no less than 155,000 words were despatched and received
in the sixty minutes. This average--2580 words per minute, 43 per
second--is truly remarkable! Even between New York and Chicago,
separated by 950 odd miles, the wires kept up an average of 1000 per
minute.The apparatus that produces these marvellous results is of two types.
The one type records messages in the Morse alphabet, the other makes
clearly-written longhand characters. The former is the faster of the
two, but the legibility of the other more than compensates for the
decrease of speed by one-half.[Illustration: _Specimens of the punched tape used for transmitting
messages by the Pollak-Virag system, and of a message as it is
delivered by the receiving machine._]The Morse alphabet method closely resembles the Wheatstone system. The
message is prepared for transmission by being punched on a tape. But
there is this difference in the position of the holes, that whereas in
the Wheatstone method two holes are used for each dot and dash, only
one is required in the Pollak-Virag. If to the right of the central
guiding line it signifies a "dash," if to the left, a "dot."The "reversal-of-current" method, already explained, causes at the
receiver end an increase or decrease in the power of a permanent
magnet to attract or repel a diaphragm, the centre of which is
connected by a very fine metal bar with the centre of a tiny mirror
hinged at one side on two points. A very slight movement of the
diaphragm produces an exaggerated movement of the mirror, which, as it
tilts backwards and forwards, reflects the light from an electric lamp
on to a lens, which concentrates the rays into a bright spot, and
focuses them on to a surface of sensitised paper.In their earliest apparatus the inventors attached the paper to the
circumference of a vertical cylinder, which revolved at an even pace
on an axle, furnished at the lower end with a screw thread, so that
the portion of paper affected by the light occupied a spiral path from
top to bottom of the cylinder.In a later edition, however, an endless band of sensitised paper is
employed, and the lamp is screened from the mirror by a horizontal
mantle in which is cut a helical slit making one complete turn of the
cylinder in its length. The mantle is rotated in unison with the
machinery driving the sensitised band; and as it revolves, the spot at
which the light from the filament can pass through the slit to the
mirror is constantly shifting from right to left, and the point at
which the reflected light from the mirror strikes the sensitised paper
from left to right. At the moment when a line is finished, the right
extremity of the mantle begins to pass light again, and the bright
spot of light recommences its work at the left edge of the band, which
has now moved on a space.The movements of the mirror backwards and forwards produce on the
paper a zigzag tracing known as syphon-writing. The record, which is
continuous from side to side of the band, is a series of zigzag
up-and-down strokes, corresponding to the dots and dashes of the Morse
alphabet.The apparatus for transmitting longhand characters is more complicated
than that just described. Two telephones are now used, and the punched
tape has in it five rows of perforations.If we take a copy-book and examine the letters, we shall see that they
all occupy one, two, or three bands of space. For instance, _a_,
between the lines, occupies one band; _g_, two bands; and _f_, three.
In forming letters, the movements of the fingers trace curves and
straight lines, the curves being the resultants of combined horizontal
and vertical movements.Messrs. Pollak and Virag, in order to produce curves, were obliged to
add a second telephone, furnished also with a metal bar joined to the
mirror, which rests on three points instead of on two. One of these
points is fixed, the other two represent the ends of the two diaphragm
bars, which move the mirror vertically and horizontally respectively,
either separately or simultaneously.A word about the punched paper before going further. It contains, as
we have said, five rows of perforations. The top three of these are
concerned only with the up-and-down strokes of the letters, the bottom
two with the cross strokes. When a hole of one set is acting in unison
with a hole of the other set a composite movement or curve results.The topmost row of all sends through the wires a negative current of
known strength; this produces upward and return strokes in the upper
zone of the letters: for instance, the upper part of a _t_. The second
row passes _positive_ currents of equal strength with the negative,
and influences the up-and-down strokes of the centre zone, _e.g._
those of _o_; the third row passes positive currents _twice_ as strong
as the negative, and is responsible for double-length vertical strokes
in the centre and lower zones, _e.g._ the stroke in _p_.In order that the record shall not be a series of zigzags it is
necessary that the return strokes in the vertical elements shall be on
the same path as the out strokes; and as the point of light is
continuously tending to move from left to right of the paper there
must at times be present a counteracting tendency counterbalancing it
exactly, so that the path of the light point is purely vertical. At
other times not merely must the horizontal movements balance each
other, but the right-to-left element must be stronger than the
left-to-right, so that strokes such as the left curve of an _e_ may be
possible. To this end rows 4 and 5 of the perforations pass currents
working the second telephone diaphragm, which moves the mirror on a
vertical axis so that it reflects the ray horizontally.It will be noticed that the holes in rows 3, 4, 5 vary in size to
permit the passage of currents during periods of different length. In
this manner the little junction-hooks of such letters as _r_, _w_,
_v_, _b_ are effected.As fast as the sensitised paper strip is covered with the movements of
the dancing spot of light it is passed on over rollers through
developing and fixing chemical baths; so that the receiving of
messages is purely automatic.The reader can judge for himself the results of this ingenious system
as shown in a short section of a message transmitted by Mr. Pollak.
The words shown actually occupied two seconds in transmission. They
are beautifully clear.It is said that by the aid of a special "multiplex" device thirty sets
of Pollak-Virag apparatus can be used simultaneously on a line! The
reader will be able, by the aid of a small calculation, to arrive at
some interesting figures as regards their united output.