THE WIRELESS TELEGRAPH UP TO THE MINUTE
THE SCIENTIST TALKS OF AMATEUR WIRELESS OPERATORS--THE GREAT
DEVELOPMENT OF WIRELESS THAT HAS ENABLED IT TO SAVE ABOUT THREE
THOUSAND LIVES--LONG DISTANCE WORK OF THE MODERN INSTRUMENTS
While the inspiring stories of Jack Binns of the steamship
_Republic_, and of J. G. Phillips and Harold S. Bride of the
ill-fated _Titanic_ are fresh in our minds, it is not necessary
to say that within the last few years the wireless telegraph has
established itself as indispensable to the safe navigation of the
seas. The story of its development is a marvellous one when we
think that it was only in December of 1901 that Marconi received
the first signal ever transmitted across the Atlantic Ocean without
wires. Now, as every boy knows, all the big steamships are equipped
with wireless, all the governments of the world operate their own
stations to communicate with their warships, at sea, and thousands
upon thousands of boy amateurs operate their own little plants with
complete success.
More wonderful still is the story when we think that by the use of
this invention a total of about three thousand persons have been
saved from death in shipwrecks. Nowhere in the pages of all history
are there any more thrilling stories of heroism and devotion to duty
than those of the men who, in the face of death themselves, have
stuck by their keys sending out over the waves the "C. Q. D." and the
"S. O. S." signals, which as every boy knows are the wireless calls
for help.
The scientist and his boy friend never tired of talking of these
things, for the young man was one of the many amateurs who had
mastered the art, so that many a night as he sat at his receiver he
caught the messages of steamships far out on the broad Atlantic, and
heard the Navy Yard station transmitting orders to Uncle Sam's ships
at sea.
One day shortly after the _Titanic_ disaster the boy said to his
friend: "I saw by the paper to-day that they are talking of passing a
law to prevent the amateur wireless operators from working. I don't
think they ought to do that. I'm sure most amateurs never interfere
with any signals, as was said they did in connection with the
messages to and from ships that went to the rescue of the _Titanic_."
"So long as the amateurs do not have powerful sending apparatus,"
answered the scientist, "I don't think they will make any serious
trouble, for it makes no confusion to have them 'listening in'
on the passing radiographs. Of course with a powerful sender a
mischievous person could work irreparable damage by sending fake
messages of one kind or another. In fact there have been several
instances of messages that were thought to be fakes, but I am sure no
boy with the intelligence to rig up a wireless outfit, would be so
lacking in understanding of his responsibilities as to try to confuse
traffic.
"But it would be a shame to stop the amateurs altogether," he
continued, "for, no matter what the companies may say, the wireless
telegraph is still in an experimental stage, and we must look to the
bright boys who are studying it now, for its greatest development.
The marvellous strides in improving the apparatus, and solving the
mysteries of electro-magnetic currents, that have been made in the
last dozen years, should be eclipsed in the next decade, if young
men with some practical experience and a desire to get at the real
scientific basis of the art, work at it."
"What are some of the main improvements of the last few years?" asked
the boy.
For answer, the scientist and the boy made a journey down to the
steamship docks, and visited the wireless cabins of several of the
big transatlantic liners. They also went to the Brooklyn Navy Yard,
where there is a wireless school, that turns out Navy operators after
a thorough course in all the various branches of the art. While on
vacations to the seashore, the youth had visited some of the big
high-power stations that send and receive messages to and from the
ships at sea.
In talking to the operators and electricians the boy learned much
about the wide extent to which wireless is used nowadays. The law
passed by Congress in the United States in 1911, making it necessary
for every passenger steamer sailing from American ports with fifty
or more passengers, to carry a wireless outfit capable of working
at least 100 miles, in charge of a licensed operator, capable of
transmitting 20 or more words a minute, did a great deal to increase
the use of wireless. Also, not only the actions of one government but
the concerted action of all the civilized nations represented at the
various international wireless conferences have brought it to the
official notice of the whole world.
Thus it has become a commercial reality on the sea, and the Great
Lakes, and also it has become a big factor in war. All of the
nations, besides having their warships equipped with wireless, now
have wireless squads in the army, and have small compact apparatus
that can be transported in small wagons, or even on horses' backs.
These portable army wireless outfits are very valuable for the
communication between detachments of an army, particularly in
places where there are few disturbing elements to intercept the
electro-magnetic waves.
In the recent campaign in Tripoli, in the war between Italy and
Turkey, the wireless was extensively used by the Italian army in the
field, and it was found that the messages radiated over the desert
just about as well as over the sea. Of course as will be seen later,
it is not meant here to convey the idea that wireless cannot be sent
over the land, for the electro-magnetic waves travel through the
ether in every direction, and as the ether fills the whole universe,
mountains, buildings, or water just as well as the air, the waves
are thought to go through obstacles as well as over water. The
difficulty in sending over land, is that there are various electrical
disturbances that intercept and confuse the wireless waves. In other
words, wireless works through mere physical obstructions without
any difficulty, just so long as certain little known electrical
disturbances do not interfere. Just think of the thousands and
thousands of wireless messages that are passing through the ether
every hour of the day and night. And yet the scientists really know
very little about the laws that govern them!
One of the instances of the strange antics of wireless was told
to the boy by an operator who had been in charge of the wireless
outfit on a Hudson River boat. He said that he and the operators on
the other boats were able to communicate with a station on shore
until they had passed the Poughkeepsie bridge, and the great steel
and stone structure stretched between the boat and the station.
Immediately communication stopped short and all efforts failed to
get any response. A series of experiments proved that the obstruction
was at the bridge, but whether it was some electrical property in
the bridge itself, or in the hills on each side of the bridge, they
have never been able to find out, and the land station was finally
discontinued.
This is just an instance of what the scientists do _not_ know about
wireless, but it shows the many boy amateurs that there are still
worlds for them to conquer in scientific research.
The central principle upon which the wireless telegraph works now is
the same as it was when Marconi, through his marvellous invention,
first received a signal from the other side of the Atlantic Ocean,
but the inventors have learned much more about the details of the
theory and it is in the improvement of devices for applying these
laws of electricity that the development has been, rather than in the
discovery of new theories. Nikola Tesla's invention for the wireless
transmission of power by earth waves is a revolutionary departure
from the usual wireless practice, but as we saw in the earlier
chapter on this subject the Tesla invention has not yet been put in
practical operation.
Though Guglielmo Marconi did not discover the laws of electricity
upon which his invention is based, to him belongs all the credit
for making use of the discoveries of the scientists of his day, and
working out from them a practical system of wireless communication.
As many boys know, the wireless telegraph is possible through the
radiation of electric waves. For instance, if a stone is thrown into
a pool waves are started out in every direction from the point where
the water is disturbed. The water does not move except up and down,
and yet the waves pass on until they reach the side of the pool, or
their force is expended.
The scientists before Marconi found out that when an electric spark
was made to jump between two magnetic poles it started electric waves
in every direction, much like the stone thrown into the pool, except
at a speed that is reckoned at 186,000 miles per second.
Prof. Amos Dolbear, of Tufts College, Massachusetts, first made
use of these waves in 1880, and a few years later Doctor Hertz,
conducting experiments along the same lines, discovered them. Since
that time these waves have been called Hertzian waves.
For many years scientists had understood that electrical waves or
vibrations travelled through the ether in a copper wire, and that
gave us telegraphy by wires, but it was a new thing to think of the
waves travelling in every direction through space without wires.
These early investigators found out that they could detect these
waves by a device called a Hertzian loop, which was simply a copper
wire bent into a hoop with the two ends close together but not
touching. A spark would appear between the ends of the wire when the
electric waves were sent out.
Marconi began his work where these scientists left off, as a very
young man on his father's farm in Italy, but soon went to England, of
which country his mother was a native, and placed the results of his
experiments before the government authorities. Continuing his labors
he soon had his wireless apparatus worked out in the form in which it
first became known to the world.
It consisted of a transmitter, receiving machine or detector, and a
set of antennæ or aerial wires from which the electrical waves were
sent. For his transmitter, he created a spark between the two brass
knobs on the ends of two thick brass wires by closing and opening an
electrical circuit with a key, very much like, but somewhat larger
than the regulation telegraph key. The space between the knobs was
called the spark gap. For a dash he would hold down his key and
make a large spark, and for a dot he would release his key quickly
and make only a short one. Thus, he could send the regular Morse or
Continental telegraphic codes of dots and dashes. These impulses were
transmitted by wires to the aerial wires, or antennæ. The impulses
left the antennæ as electro-magnetic waves, and went forth in all
directions, only to be caught on the antennæ of another station
aboard a ship or on land.
Here is where the receiver did its work, and the problem was a far
more difficult one than the working out of the transmitter, for the
waves as received were too weak in themselves to register a dot
or a dash. In Marconi's first instruments he used a device called
the "coherer." This was a glass tube about as big around as a lead
pencil, and perhaps two inches long. It was plugged at each end with
silver, and the narrow space between the plugs was filled with finely
powdered fragments of nickel and silver, which possess the strange
property of being alternately very good and very bad electrical
conductors. The waves in Marconi's first experiments were received
on a suspended kite wire, exactly similar to the wire used in the
transmitter, but they were so weak that they could not of themselves
operate an ordinary telegraph instrument. They possessed strength
enough, however, to draw the little particles of silver and nickel
in the coherer together in a continuous metal path. In other words,
they made these particles "cohere," and the moment they cohered they
became a good conductor for electricity, and a current from a battery
near at hand rushed through the connection, operated the Morse
instrument, and caused it to print a dot or a dash; then a little
tapper, actuated by the same current, struck against the coherer, the
particles of metal were broken apart, becoming a poor conductor, and
cutting off the current from the home battery.
In Marconi's early experiments there was little or no attempt at
tuning the instruments for waves of certain lengths, but this art has
been developed to a high state in modern wireless telegraphy and we
shall see how the operator tunes his instruments to talk to any one
special station.
The distinguishing feature of the modern wireless transmitter, now
familiar to every boy who has ever taken a trip aboard a large ship,
or attended an electrical show, as it was in the old days, is the
"crack, crack, cr-r-r-ack, crack" of the spark as it flickers between
the brass knobs of the instrument, as the operator pounds away at
his key. In some of the great high-power land stations, where long
distance work is done the crash of the spark is like that of thunder,
the flame is as big around as a man's wrist and of such intensity
that it could not be looked at with unshaded eyes. On ships where the
crash is too loud it has become necessary to cover the spark gap with
a wooden muffler so as to deaden the noise.
While the simple spark gap of the early Marconi instruments was
enough to send out the Hertzian waves, the modern transmitter is a
marvel of electrical construction utilizing as it does the latest
discoveries in electrical apparatus.
The most noticeable difference in the sending apparatus is in the
arrangement of the two wires between which the spark flies. In the
early instruments the wires were set in a horizontal line, and
connected to an induction coil, but in the later ones the oscillator
was turned up lengthwise with the spark gap between the vertical
wings.
The different position of the spark gap is a change only in form, and
not in principle. In the Marconi apparatus used nowadays the current
comes from a dynamo of more than 110 volts, direct current. The two
terminals of the circuit are connected with an induction coil, and
from there to the two ends of the wires, making the terminals of the
spark gap. The upper wire runs from the spark gap to the aerial,
and the lower runs through a battery of Leyden jars, through a high
tension transformer (as does the other side of the circuit), and
thence to the ground. Aboard ship the ground connection is simply
made by attaching a wire to the hull of the ship, which is in
connection with the water, the best possible earth connection.
[Illustration: MARCONI TRANSMITTER LAYOUT
A--Key.
B--Induction coil.
C--Spark gap.
D--Dynamo.
E--Rheostat.
F--Interrupter magnet.
G--Aerial.
H--High tension transformer.
I--Ground wire.
K--Battery of Leyden jars.]
There are, of course, a great many different kinds of
transmitters, but they are all worked out on the same general
principle--a spark gap which creates electrical oscillations that
are sent into the ether from the aerials.
In some modern stations an alternating current is used at more
than 100 volts and is stepped up through a transformer to about
30,000 volts. This high power current then charges a condenser
consisting of a battery of Leyden jars.
When the operator presses his key he establishes a connection,
which immediately sets up electrical waves oscillating at a
rate of anywhere from 100,000 to 2,500,000 per second. These
oscillations are carried to the antennæ where they pass into the
ether and spread in all directions to be caught on the aerials of
all stations within range.
One of the improvements in wireless transmission which makes
long distance work possible aboard ships is the use of what the
engineers call "coupled circuits." The arrangement consists
in connecting the aerial to an induction coil, and connecting
the latter with a ground wire. Another coil is placed close to
this and is connected with the spark gap, and a condenser. The
period of oscillation of the antennæ circuit, and of the spark
gap circuit are timed to be exactly the same. The two circuits
are then called "coupled circuits," for while they are coupled
together by induction only, the oscillation or spark gap circuit
increases its capacity, and at the same time has a small spark
gap.
With these new devices for increasing the power of the
oscillations, or in other words throwing a bigger stone into the
pond, the electrical waves are sent out with far greater force,
just as the water waves are sent farther in the pond, and will
reach stations at a greater distance.
"Crash, bang," goes the oscillator, and in less time than it
takes to think it the oscillations have reached the antennæ of
ships hundreds or thousands of miles away, or even those of
another land station on the other side of the Atlantic Ocean.
The next thing is to understand the apparatus used for receiving
the faint electric waves transmitted through the ether, for the
modern instruments are far different from the old style "coherer"
explained before. As with the spark gaps, there are many
different styles of receiving devices, all known by the general
name of "detectors," as they detect the faint electro-magnetic
waves radiating through the ether.
Some of the latest Marconi experiments show a return to the
"coherer" idea, very greatly improved upon, but the full details
of the device have not been made public.
[Illustration:
Courtesy of the New York Edison Co.
THE NAVY WIRELESS SCHOOL
At top is the class in sending, while below is shown the class
learning to receive messages.]
[Illustration: AN AMATEUR WIRELESS OUTFIT
Hundreds of boys are receiving and sending wireless messages with
far less efficient apparatus than that shown here.]
[Illustration: MARCONI DETECTOR LAYOUT
A--Aerial.
B--Condenser.
C--Glass tube oscillator transformer.
D--D´--Rollers.
E--E´--Iron wire passing through oscillator transformer.
F--F´--Magnets.
G--G´--Ground wires.
H--Telephone receiver.]
One of the detecting devices used by the Marconi system, after
the old-style "coherer" was done away with, was very simple
indeed in comparison to the cohering and tapping machines. It
was made up of a small glass tube wound with copper wire. One
end of this made the ground connection, and the other end led
to the aerial, and also to an earth connection through a tuning
inductance coil. Then another coil was wound around the first
one on the glass tube and connected with the head telephone
receivers which have taken the place of the Morse dot and dash
printing instrument in all the modern wireless instruments. Two
magnets were placed just above the glass tube, and a flexible
iron wire was made to move through it by means of a pair of
rollers a little way from each end. When the electro-magnetic
waves reached the aerial and made oscillations in the first coil
about the glass tube, the magnetic intensity of the iron wire
band was disturbed and the glass tube became an oscillation
transformer, setting up currents in the coil leading to the
telephone receivers. The impulses were manifested by ticks, just
the length of the dots and dashes being sent out by the operator
perhaps thousands of miles away.
Another form of detector is the "electrolytic" which consists of
a very fine platinum wire about one ten-thousandth of an inch in
diameter, which dips into a platinum cup filled with nitric acid.
When the invisible electro-magnetic waves impinge upon the wires
of the receiving station, and cause electrical surges to take
place in those wires, they in turn affect the detector, giving an
exact reproduction of the note of the transmitting spark at the
distant station.
This device has since been replaced by one of another type,
equally sensitive and much better suited for general work on
account of its greater stability and freedom from atmospheric
disturbances. This detector consists simply of a crystal of
carborundum supported between two brass points. When connected to
the antennæ it is affected by the oscillations caused by distant
transmitting stations as previously stated. These wireless
signals are reproduced in telephone receivers.
Another frequently used detector known as the Audion is composed
of a small incandescent lamp with filaments of carbon, tantalum,
or preferably tungsten, and one or more sheets or wings of
platinum secured near the filaments. The lamp is lighted by a
set of home batteries, and is connected with a ground wire, the
aerial, and the telephone receivers. The tungsten filament and
the platinum wing act as two electrodes, and the faint electric
oscillations received on the antennæ and transmitted to the
platinum plate are supposed to affect the discharge of negatively
electrified particles, or ions, between the two electrodes.
This affects the flow of the battery current, and consequently
registers the oscillations in the telephone receivers.
By diligent study of the subject the wireless experts also
have learned that the arrangement of the aerials is of great
importance, because much depends upon the send-off received by
the electrical oscillations. In Marconi's early experiments he
used a single wire attached to a kite, then changed to a single
wire stretched from the top of a high mast. Later, the system of
stretching the wires horizontally between two masts, as we see
them so often aboard passenger steamships, and at land stations,
came into general use. The old idea that the height of the aerial
wires had something to do with the efficiency of the apparatus
has passed, for science showed that the electro-magnetic waves
travelled in all directions irrespective of land, water,
mountains, or buildings. Whether, in sending messages across the
ocean, they actually pass through the globe, or follow the curve
of the surface, is more than the most careful wireless students
have been able to tell.
Another of the big improvements in wireless is in the tuning of
the instruments to certain wave lengths or rates of vibrations,
and in controlling the wave lengths by the sender. Science has
established that these waves usually vary from a few feet up
to 12,000 feet or more. The ordinary wave lengths for ships
is between 1,000 feet and 1,800 feet, but on the biggest land
stations and the transatlantic liners the full 12,000 feet is
used. Even greater lengths of waves are used by the big Marconi
stations transmitting messages between Clifden, on the west coast
of Ireland, and Glace Bay, Nova Scotia. The reason for this is
that with the same power messages can be sent greater distances
with long wave lengths than with shorter ones.
The wave length is controlled by an apparatus called the "helix,"
which may be seen in the picture of the wireless outfit. It looks
like a drum wound with a spiral of copper tubing, and although
it looks simple it presents some of the greatest problems in
connection with wireless.
On the receiving end is the instrument called the tuner, by which
the operator can adjust his detector to the wave lengths being
sent out by the station with which he wishes to talk. There are
various kinds of "tuners," all more or less complicated. The
device corresponds to the telephone exchange or the telegraph
switch-board. Of course a good receiving apparatus can be tuned
so that the operator can listen to any messages going through
the ether, within range, but all messages that are intended to
be secret are sent in code, just as all wire and cable messages
that are secret are sent in code.
In line with the advent of wireless telegraphy it is fitting that
we should have the wireless telephone. While this instrument is
still in the experimental stage, some very promising results have
been obtained. There are several experimental wireless telephone
stations in New York City, but the best results are obtained when
some one keeps up a steady conversation, so it is far easier to
connect the reproducer of a phonograph to the transmitter of the
wireless telephone. It is surprising how distinctly this music or
speech is received. In fact the ship operators nearing New York
are often entertained by strains of music from these wireless
telephones. The wireless telephones employ what are known as
undamped oscillations created by electric arcs, and it is very
easy to "tune out" such vibrations for musical effects.
Just as we have the motion-picture "newspaper," we have the
wireless newspaper published aboard the big transatlantic liners
every day. The news is sent out from certain land stations at
certain times in the day and night, and every ship within range
copies it, and publishes it just as our regular daily papers are
published. Of course, the paper is small, but it usually contains
most of the important news of the day, the big sporting items,
such as baseball scores, and the stock quotations.
In the United States the great station at Wellfleet, Cape Cod,
Mass., sends out the press matter each night from dispatches
prepared in the main offices of the big American press
associations. Ships as far as 1,600 miles distant frequently
receive this news matter, and by the time the ocean-going editor
is ready to get out his next day's edition he is in touch with
the wireless press station on the other side, and is receiving
the world's news from the English coast.
As our young friend found out when he was gathering up all the
information he could about aeroplanes, some success has been made
in the equipment of the fliers with wireless. The project offers
some serious difficulties, however, as on an aeroplane there is
no place for long aerials. Experiments have been tried with long
trailing wires, but these are dangerous to the aeroplane, and to
use the wires of the machine for antennæ endangers the operator
to electric shocks. One scheme tried by several aviators in the
United States with some success has been the stringing of aerials
in the rear framework.
The problem of equipping balloons and airships with wireless is
much simpler because it allows of long trailing wires to act as
the antennæ. Most boys will remember the success of the wireless
apparatus that was set up on the _America_ at the time Walter
Wellman made his famous attempt to cross the Atlantic in his
airship.
That wireless will take its place as one of the great forces in
civilization is the idea of Guglielmo Marconi, the inventor of
the wireless telegraph, expressed when he was in New York in the
spring of 1912.
"I believe," he said, "that in the near future a wireless message
will be sent from New York completely round the globe with no
relaying, and will be received by an instrument located in the
same office as the transmitter, in perhaps even less time than
Shakespeare's forty minutes.
"Most messages across the Atlantic will probably go by wireless
at a comparatively early date. In time of war wireless
connections will be invaluable. The enemy can cut cables and
telegraph wires; but it is difficult seriously to damage the
wireless service. The British Empire has realized this, and is
already equipping many of its outposts with wireless stations."