WIRELESS TELEGRAPHY
Primitive Signalling--Principles of Wireless Telegraphy--Ether
Vibrations--Wireless Apparatus--The Marconi System.
At a very early stage in the world's history, man found it necessary
to be able to communicate with places at a distance by means of signals.
Fire was the first agent employed for the purpose. On hill-tops or
other eminences, what were known as beacon fires were kindled and owing
to their elevation these could be seen for a considerable distance
throughout the surrounding country. These primitive signals could be
passed on from one point to another, until a large region could be
covered and many people brought into communication with one another.
These fires expressed a language of their own, which the observers
could readily interpret. For a long time they were the only method
used for signalling. Indeed in many backward localities and in some
of the outlying islands and among savage tribes the custom still
prevails. The bushmen of Australia at night time build fires outside
their huts or kraals to attract the attention of their followers.
Even in enlightened Ireland the kindling of beacon fires is still
observed among the people of backward districts especially on May Eve
and the festival of mid-summer. On these occasions bonfires are lit
on almost every hillside throughout that country. This custom has been
handed down from the days of the Druids.
For a long time fires continued to be the mode of signalling, but as
this way could only be used in the night, it was found necessary to
adopt some method that would answer the purpose in daytime; hence
signal towers were erected from which flags were waved and various
devices displayed. Flags answered the purposes so very well that they
came into general use. In course of time they were adopted by the army,
navy and merchant marine and a regular code established, as at the
present time.
The railroad introduced the semaphore as a signal, and field tactics
the heliograph or reflecting mirror which, however, is only of service
when there is a strong sunlight.
Then came the electric telegraph which not only revolutionized all
forms of signalling but almost annihilated distance. Messages and all
sorts of communications could be flashed over the wires in a few minutes
and when a cable was laid under the ocean, continent could converse
with continent as if they were next door neighbors.
The men who first enabled us to talk over a wire certainly deserve our
gratitude, all succeeding generations are their debtors. To the man
who enabled us to talk to long distances without a wire at all it would
seem we owe a still greater debt. But who is this man around whose
brow we should twine the laurel wreath, to the altar of whose genius
we should carry frankincense and myrrh?
This is a question which does not admit of an answer, for to no one
man alone do we owe wireless telegraphy, though Hertz was the first
to discover the waves which make it possible. However, it is to the
men whose indefatigable labors and genius made the electric telegraph
a reality, that we also owe wireless telegraphy as we have it at
present, for the latter may be considered in many respects the resultant
of the former, though both are different in medium.
Radio or wireless telegraphy in principle is as old as mankind. Adam
delivered the first wireless when on awakening in the Garden of Eden
he discovered Eve and addressed her in the vernacular of Paradise in
that famous sentence which translated in English reads both ways the
same,--"Madam, I'm Adam." The oral words issuing from his lips created
a sound wave which the medium of the air conveyed to the tympanum of
the partner of his joys and the cause of his sorrows.
When one person speaks to another the speaker causes certain vibrations
in the air and these so stimulate the hearing apparatus that a series
of nerve impulses are conveyed to the sensorium where the meaning of
these signals is unconsciously interpreted.
In wireless telegraphy the sender causes vibrations not in the air but
in that all-pervading impalpable substance which fills all space and
which we call the ether. These vibrations can reach out to a great
distance and are capable of so affecting a receiving apparatus that
signals are made, the movements of which can be interpreted into a
distinct meaning and consequently into the messages of language.
Let us briefly consider the underlying principles at work. When we
cast a stone into a pool of water we observe that it produces a series
of ripples which grow fainter and fainter the farther they recede from
the centre, the initial point of the disturbance, until they fade
altogether in the surrounding expanse of water. The succession of these
ripples is what is known as _wave_ motion.
When the clapper strikes the lip of a bell it produces a sound and
sends a tremor out upon the air. The vibrations thus made are air
waves.
In the first of these cases the medium communicating the ripple or
wavelet is the water. In the second case the medium which sustains the
tremor and communicates the vibrations is the air.
Let us now take the case of a third medium, the substance of which
puzzled the philosophers of ancient time and still continues to puzzle
the scientists of the present. This is the ether, that attenuated fluid
which fills all inter-stellar space and all space in masses and between
molecules and atoms not otherwise occupied by gross matter. When a
lamp is lit the light radiates from it in all directions in a wave
motion. That which transmits the light, the medium, is ether. By this
means energy is conveyed from the sun to the earth, and scientists
have calculated the speed of the ether vibrations called light at
186,400 miles per second. Thus a beam of light can travel from the sun
to the earth, a distance of between 92,000,000 and 95,000,000 miles
(according to season), in a little over eight minutes.
The fire messages sent by the ancients from hill to hill were ether
vibrations. The greater the fires, the greater were the vibrations and
consequently they carried farther to the receiver, which was the eye.
If a signal is to be sent a great distance by light the source of that
light must be correspondingly powerful in order to disturb the ether
sufficiently. The same principle holds good in wireless telegraphy.
If we wish to communicate to a great distance the ether must be
disturbed in proportion to the distance. The vibrations that produce
light are not sufficient in intensity to affect the ether in such a
way that signals can be carried to a distance. Other disturbances,
however, can be made in the ether, stronger than those which create
light. If we charge a wire with an electric current and place a magnetic
needle near it we find it moves the needle from one position to another.
This effect is called an electro-magnetic disturbance in the ether.
Again when we charge an insulated body with electricity we find that
it attracts any light substance indicating a material disturbance in
the ether. This is described as an electro-static disturbance or effect
and it is upon this that wireless telegraphy depends for its operations.
The late German physicist, Dr. Heinrich Hertz, Ph.D., was the first
to detect electrical waves in the ether. He set up the waves in the
ether by means of an electrical discharge from an induction coil. To
do this he employed a very simple means. He procured a short length
of wire with a brass knob at either end and bent around so as to form
an almost complete circle leaving only a small air gap between the
knobs. Each time there was a spark discharge from the induction coil,
the experimenter found that a small electric spark also generated
between the knobs of the wire loop, thus showing that electric waves
were projected through the ether. This discovery suggested to scientists
that such electric waves might be used as a means of transmitting
signals to a distance through the medium of the ether without connecting
wires.
When Hertz discovered that electric waves crossed space he unconsciously
became the father of the modern system of radio-telegraphy, and though
he did not live to put or see any practical results from his wonderful
discovery, to him in a large measure should be accorded the honor of
blazoning the way for many of the intellectual giants who came after
him. Of course those who went before him, who discovered the principles
of the electric telegraph made it possible for the Hertzian waves to
be utilized in wireless.
It is easy to understand the wonders of wireless telegraphy when we
consider that electric waves transverse space in exactly the same
manner as light waves. When energy is transmitted with finite velocity
we can think of its transference only in two ways: first by the actual
transference of matter as when a stone is hurled from one place to
another; second, by the propagation of energy from point to point
through a medium which fills the space between two bodies. The body
sending out energy disturbs the medium contiguous to it, which
disturbance is communicated to adjacent parts of the medium and so the
movement is propagated outward from the sending body through the medium
until some other body is affected.
A vibrating body sets up vibrations in another body, as for instance,
when one tuning fork responds to the vibrations of another when both
have the same note or are in tune.
The transmission of messages by wireless telegraphy is effected in a
similar way. The apparatus at the sending station sends out waves of
a certain period through the ether and these waves are detected at the
receiving station, by apparatus attuned to this wave length or period.
The term electric radiation was first employed by Hertz to designate
waves emitted by a Leyden jar or oscillator system of an induction
coil, but since that time these radiations have been known as Hertzian
waves. These waves are the underlying principles in wireless telegraphy.
It was found that certain metal filings offered great resistance to
the passage of an electric current through them but that this resistance
was very materially reduced when electric waves fell upon the filings
and remained so until the filings were shaken, thus giving time for
the fact to be observed in an ordinary telegraphic instrument.
The tube of filings through which the electric current is made to pass
in wireless telegraphy is called a coherer signifying that the filings
cohere or cling together under the influence of the electric waves.
Almost any metal will do for the filings but it is found that a
combination of ninety per cent. nickel and ten per cent. silver answers
the purpose best.
The tube of the coherer is generally of glass but any insulating
substance will do; a wire enters at each end and is attached to little
blocks of metal which are separated by a very small space. It is into
this space the filings are loosely filled.
Another form of coherer consists of a glass tube with small carbon
blocks or plugs attached to the ends of the wires and instead of the
metal filings there is a globule of mercury between the plugs. When
electric waves fall upon this coherer, the mercury coheres to the
carbon blocks, and thus forms a bridge for the battery current.
Marconi and several others have from time to time invented many other
kinds of detectors for the electrical waves. Nearly all have to serve
the same purpose, viz., to close a local battery circuit when the
electric waves fall upon the detector.
There are other inventions on which the action is the reverse. These
are called anti-coherers. One of the best known of these is a tube
arranged in a somewhat similar manner to the filings tube but with two
small blocks of tin, between which is placed a paste made up of alcohol,
tin filings and lead oxide. In its normal state the paste allows the
battery current to get across from one block to another, but when
electric waves touch it a chemical action is produced which immediately
breaks down the bridge and stops the electric waves, the paste resumes
its normal condition and allows the battery current to pass again.
Therefore by this arrangement the signals are made by a sudden breaking
and making of the battery circuit.
Then there is the magnetic detector. This is not so easy of explanation.
When we take a piece of soft iron and continuously revolve it in front
of a permanent magnet, the magnetic poles of the soft iron piece will
keep changing their position at each half revolution. It requires a
little time to effect this magnetic change which makes it appear as
if a certain amount of resistance was being made against it. (If
electric waves are allowed to fall upon the iron, resistance is
completely eliminated, and the magnetic poles can change places
instantly as it revolves.)
From this we see that if we have a quickly changing magnetic field it
will induce or set up an electric current in a neighboring coil of
wire. In this way we can detect the changes in the magnetic field, for
we can place a telephone receiver in connection with the coil of wire.
In a modern wireless receiver of this kind it is found more convenient
to replace the revolving iron piece by an endless band of soft iron
wire. This band is kept passing in front of a permanent magnet, the
magnetism of the wire tending to change as it passes from one pole to
the other. This change takes place suddenly when the electric waves
form the transmitting station, fall upon the receiving aerial conductor
and are conducted round the moving wire, and as the band is passing
through a coil of insulated wire attached to a telephone receiver,
this sudden change in the magnetic field induces an electric current
in the surrounding coil and the operator hears a sound in the telephone
at his ear. The Morse code may thus be signalled from the distant
transmitter.
There are various systems of wireless telegraphy for the most part
called after the scientists who developed or perfected them. Probably
the foremost as well as the best known is that which bears the name
of Marconi. A popular fallacy makes Marconi the discoverer of the
wireless method. Marconi was the first to put the system on a commercial
footing or business basis and to lead the way for its coming to the
front as a mighty factor in modern progress. Of course, also, the honor
of several useful inventions and additions to wireless apparatus must
be given him. He started experimenting as far back as 1895 when but
a mere boy. In the beginning he employed the induction coil, Morse
telegraph key, batteries, and vertical wire for the transmission of
signals, and for their reception the usual filings coherer of nickel
with a very small percentage of silver, a telegraph relay, batteries
and a vertical wire. In the Marconi system of the present time there
are many forms of coherers, also the magnetic detector and other
variations of the original apparatus. Other systems more or less
prominent are the Lodge-Muirhead of England, Braun-Siemens of Germany
and those of DeForest and Fessenden of America. The electrolytic
detector with the paste between the tin blocks belongs to the system
of DeForest. Besides these the names of Popoff, Jackson, Armstrong,
Orling, Lepel, and Poulsen stand high in the wireless world.
A serious drawback to the operations of wireless lies in the fact that
the stations are liable to get mixed up and some one intercept the
messages intended for another, but this is being overcome by the
adoption of a special system of wave lengths for the different wireless
stations and by the use of improved apparatus.
In the early days it was quite a common occurrence for the receivers
of one system to reply to the transmitters of a rival system. There
was an all-round mix-up and consequently the efficiency of wireless
for practical purposes was for a good while looked upon with more or
less suspicion. But as knowledge of wave motions developed and the
laws of governing them were better understood, the receiver was "tuned"
to respond to the transmitter, that is, the transmitter was made to
set up a definite rate of vibrations in the ether and the receiver
made to respond to this rate, just like two tuning forks sounding the
same note.
In order to set up as energetic electric waves as possible many methods
have been devised at the transmitting stations. In some methods a wire
is attached to one of the two metal spheres between which the electric
charge takes place and is carried up into the air for a great height,
while to the second sphere another wire is connected and which leads
into the earth. Another method is to support a regular network of wires
from strong steel towers built to a height of two hundred feet or more.
Long distance transmission by wireless was only made possible by
grounding one of the conductors in the transmitter. The Hertzian waves
were provided without any earth connection and radiated into space in
all directions, rapidly losing force like the disappearing ripples on
a pond, whereas those set up by a grounded transmitter with the
receiving instrument similarly connected to earth, keep within the
immediate neighborhood of the earth.
For instance up to about two hundred miles a storage battery and
induction coil are sufficient to produce the necessary ether
disturbance, but when a greater distance is to be spanned an engine
and a dynamo are necessary to supply energy for the electric waves.
In the most recent Marconi transmitter the current produced is no
longer in the form of intermittent sparks, but is a true alternating
current, which in general continues uniformly as long as the key is
pressed down.
There is no longer any question that wireless telegraphy is here to
stay. It has passed the juvenile stage and is fast approaching a lusty
adolescence which promises to be a source of great strength to the
commerce of the world. Already it has accomplished much for its age.
It has saved so many lives at sea that its installation is no longer
regarded as a scientific luxury but a practical necessity on every
passenger vessel. Practically every steamer in American waters is
equipped with a wireless station. Even freight boats and tugs are
up-to-date in this respect. Every ship in the American navy, including
colliers and revenue cutters, carries wireless operators. So important
indeed is it considered in the Navy department that a line of shore
stations have been constructed from Maine on the Atlantic to Alaska
on the Pacific.
In a remarkably short interval wireless has come to exercise an
important function in the marine service. Through the shore stations
of the commercial companies, press despatches, storm warnings, weather
reports and other items of interest are regularly transmitted to ships
at sea. Captains keep in touch with one another and with the home
office; wrecks, derelicts and storms are reported. Every operator sends
out regular reports daily, so that the home office can tell the exact
position of the vessel. If she is too far from land on the one side
to be reached by wireless she is near enough on the other to come
within the sphere of its operations.
Weather has no effect on wireless, therefore the question of meteorology
does not come into consideration. Fogs, rains, torrents, tempests,
snowstorms, winds, thunder, lightning or any aerial disturbance
whatsoever cannot militate against the sending or receiving of wireless
messages as the ether permeates them all.
Submarine and land telegraphy used to look on wireless, the youngest
sister, as the Cinderella of their name, but she has surpassed both
and captured the honors of the family. It was in 1898 that Marconi
made his first remarkable success in sending messages from England to
France. The English station was at South Foreland and the French near
Boulogne. The distance was thirty-two miles across the British channel.
This telegraphic communication without wires was considered a wonderful
feat at the time and excited much interest.
During the following year Marconi had so much improved his first
apparatus that he was able to send out waves detected by receivers up
to the one hundred mile limit.
In 1900 communication was established between the Isle of Wight and
the Lizard in Cornwall, a distance of two hundred miles.
Up to this time the only appliances employed were induction coils
giving a ten or twenty inch spark. Marconi and others perceived the
necessity of employing greater force to penetrate the ether in order
to generate stronger electrical waves. Oil and steam engines and other
appliances were called into use to create high frequency currents and
those necessitated the erection of large power stations. Several were
erected at advantageous points and the wireless system was fairly
established as a new agent of communication.
In December, 1901, at St. John's, Newfoundland, Marconi by means of
kites and balloons set up a temporary aerial wire in the hope of being
able to receive a signal from the English station in Cornwall. He had
made an arrangement with Poldhu station that on a certain date and at
a fixed hour they should attempt the signal. The letter S, which in
the Morse code consists of three successive dots, was chosen. Marconi
feverishly awaited results. True enough on the day and at the time
agreed upon the three dots were clicked off, the first signal from
Europe to the American continent. Marconi with much difficulty set up
other aerial wires and indubitably established the fact that it was
possible to send electric waves across the Atlantic. He found, however,
that waves in order to traverse three thousand miles and retain
sufficient energy on their arrival to affect a telephonic wave-detecting
device must be generated by no inordinate power.
These experiments proved that if stations were erected of sufficient
power transatlantic wireless could be successfully carried on. They
gave an impetus to the erection of such stations.
On December 21, 1902, from a station at Glace Bay, Nova Scotia, Marconi
sent the first message by wireless to England announcing success to
his colleagues.
The following January from Wellsfleet, Cape Cod, President Roosevelt
sent a congratulatory message to King Edward. The electric waves
conveying this message traveled 3,000 miles over the Atlantic following
round an arc of forty-five degrees of the earth on a great circle, and
were received telephonically, by the Marconi magnetic receiver at
Poldhu.
Most ships are provided with syntonic receivers which are tuned to
long distance transmitters, and are capable of receiving messages up
to distances of 3,000 miles or more. Wireless communication between
Europe and America is no longer a possibility but an accomplishment,
though as yet the system has not been put on a general business basis.
[Footnote: As we go to press a new record has been established in
wireless transmission. Marconi, in the Argentine Republic, near Buenos
Ayres, has received messages from the station at Clifden, County Galway,
Ireland, a distance of 5,600 miles. The best previous record was made
when the United States battleship _Tennessee_ in 1909 picked up a
message from San Francisco when 4,580 miles distant.]