THE WIRELESS TELEGRAPH.
Magnetic waves generated in the ether (see pp. 53-95) by an
electric current flowing in a conductor are not the only waves
which can be set up in it by aid of electricity. A merely
stationary or "static" charge of electricity on a body, say a
brass ball, can also disturb the ether; and if the strength of the
charge is varied, ether oscillations or waves are excited. A
simple way of producing these "electric waves" in the ether is to
vary the strength of charge by drawing sparks from the charged
body. Of course this can be done according to the Morse code; and
as the waves after travelling through the ether with the speed of
light are capable of influencing conductors at a distance, it is
easy to see that signals can be sent in this way. The first to do
so in a practical manner was Signer Marconi, a young Italian
hitherto unknown to fame. In carrying out his invention, Marconi
made use of facts well known to theoretical electricians, one of
whom, Dr, Oliver J. Lodge, had even sent signals with them in
1894; but it often happens in science as in literature that the
recognised professors, the men who seem to have everything in
their favour--knowledge, even talent--the men whom most people
would expect to give us an original discovery or invention, are
beaten by an outsider whom nobody heard of, who had neither
learning, leisure, nor apparatus, but what he could pick up for
himself.
Marconi produces his waves in the ether by electric sparks passing
between four brass balls, a device of Professor Righi, following
the classical experiments of Heinrich Hertz. The balls are
electrified by connecting them to the well-known instrument called
an induction coil, sometimes used by physicians to administer
gentle shocks to invalids; and as the working of the coil is
started and stopped by an ordinary telegraph key for interrupting
the electric current, the sparking can be controlled according to
the Morse code. In our diagram, which explains the apparatus, the
four balls are seen at D, the inner and larger pair being partly
immersed in vaseline oil, the outer and smaller pair being
connected to the secondary or induced circuit of the induction
coil C, which is represented by a wavy line. The primary or
inducing circuit of the coil is connected to a battery B through a
telegraph signalling key K, so that when this key is opened and
closed by the telegraphist according to the Morse code, the
induction coil is excited for a longer or shorter time by the
current from the battery, in agreement with the longer and shorter
signals of the message. At the same time longer or shorter series
of sparks corresponding to these signals pass across the gaps
between the four balls, and give rise to longer or shorter series
of etheric waves represented by the dotted line. So much for the
"Transmitter." But how does Marconi transform these invisible
waves into visible or audible signals at the distant place? He
does this by virtue of a property discovered by Mr. S. A. Varley
as far back as 1866, and investigated by Mr. E. Branly in 1889.
They found that powder of metals, carbon, and other conductors,
while offering a great resistance to the passage of an electric
current when in a loose state, coheres together when electric
waves act upon it, and opposes much less resistance to the
electric current. It follows that if a Morse telegraph instrument
at the distant place be connected in circuit with a battery and
some loose metal dust, it can be adjusted to work when the etheric
waves pass through the dust, and only then. In the diagram R is
this Morse "Receiver" joined in circuit with a battery B1; and a
thin layer of nickel and silver dust, mixed with a trace of
mercury, is placed between two cylindrical knobs or "electrodes"
of silver fused into the glass tube d, which is exhausted of air
like an electric glow lamp. Now, when the etheric waves proceeding
from the transmitting station traverse the glass of the tube and
act upon the metal dust, the current of the battery B1 works the
Morse receiver, and marks the signals in ink on a strip of
travelling paper. Inasmuch as the dust tends to stick together
after a wave passes through it, however, it requires to be shaken
loose after each signal, and this is done by a small round hammer
head seen on the right, which gives a slight tap to the tube. The
hammer is worked by a small electromagnet E, connected to the
Morse instrument, and another battery b in what is called a
"relay" circuit; so that after the Morse instrument marks a
signal, the hammer makes a tap on the tube. As this tap has a
bell-like sound, the telegraphist can also read the signals of the
message by his ear.
Two "self-induction bobbins," L Ll, a well-known device of
electricians for opposing resistance to electric waves, are
included in the circuit of the Morse instrument the better to
confine the action of the waves to the powder in the tube.
Further, the tube d is connected to two metal conductors V Vl,
which may be compared to resonators in music. They can be adjusted
or attuned to the electric waves as a string or pipe is to
sonorous waves. In this way the receiver can be made to work only
when electric waves of a certain rate are passing through the
tube, just as a tuning-fork resounds to a certain note; it being
understood that the length of the waves can be regulated by
adjusting the balls of the transmitter. As the etheric waves
produced by the sparks, like ripples of water caused by dropping a
stone into a pool, travel in all directions from the balls, a
single transmitter can work a number of receivers at different
stations, provided these are "tuned" by adjusting the conductors V
Vl to the length of the waves.
This indeed was the condition of affairs at the time when the
young Italian transmitted messages from France to England in
March, 1899, and it is a method that since has been found useful
over limited distances. But to the inventor there seemed no reason
why wireless telegraphy should be limited by any such distances.
Accordingly he immediately developed his method and his apparatus,
having in mind the transmission of signals over considerable
intervals. The first question that arose was the effect of the
curvature of the Earth and whether the waves follow the surface of
the Earth or were propagated in straight lines, which would
require the erection of aerial towers and wires of considerable
height. Then there was the question of the amount of power
involved and whether generators or other devices could be used to
furnish waves of sufficient intensity to traverse considerable
distances.
Little by little progress was made and in January, 1901, wireless
communication was established between the Isle of Wight and Lizard
in Cornwall, a distance of 186 miles with towers less than 300
feet in height, so that it was demonstrated that the curvature of
the Earth did not seriously affect the transmission of the waves,
as towers at least a mile high would have been required in case
the waves were so cut off. This was a source of considerable
encouragement to Marconi, and his apparatus was further improved
so that the resonance of the circuit and the variation of the
capacity of the primary circuit of the oscillation transformer
made for increased efficiency. The coherer was still retained and
by the end of 1900 enough had been accomplished to warrant Marconi
in arranging for trans-Atlantic experiments between Poldhu,
Cornwall and the United States, stations being located on Cape Cod
and in Newfoundland. The trans-Atlantic transmission of signals
was quite a different matter from working over 100 miles or so in
Great Britain. The single aerial wire was supplanted by a set of
fifty almost vertical wires, supported at the top by a horizontal
wire stretched between two masts 157 1/2 feet high and 52 1/2 feet
apart, converging together at the lower end in the shape of a
large fan. The capacity of the condenser was increased and instead
of the battery a small generator was employed so that a spark 1
1/2 inches in length would be discharged between spheres 3 inches
in diameter. At the end of the year 1901 temporary stations at
Newfoundland were established and experiments were carried on with
aerial wires raised in the air by means of kites. It was here
realized that various refinements in the receiving apparatus were
necessary, and instead of the coherer a telephone was inserted in
the secondary circuit of the oscillation transformer, and with
this device on February 12th the first signals to be transmitted
across the Atlantic were heard. These early experiments were
seriously affected by the fact that the antennae or aerial wires
were constantly varying in height with the movement of the kites,
and it was found that a permanent arrangement of receiving wires,
independent of kites or balloons, was essential. Yet it was
demonstrated at this time that the transmission of electric waves
and their detection over distances of 2000 miles was distinctly
possible.
A more systematic and thorough test occurred in February, 1902,
when a receiving station was installed on the steamship
Philadelphia, proceeding from Southampton to New York. The
receiving aerial was rigged to the mainmast, the top of which was
197 feet above the level of the sea, and a syntonic receiver was
employed, enabling the signals to be recorded on the tape of an
ordinary Morse recorder. On this voyage readable messages were
received from Poldhu up to a distance of 1551 miles, and test
letters were received as far as 2099 miles. It was on this voyage
that Marconi made the interesting discovery of the effect of
sunlight on the propagation of electric waves over great
distances. He found that the waves were absorbed during the
daytime much more than at night and he eventually reached the
conclusion that the ultraviolet light from the sun ionized the
gaseous molecules of the air, and ionized air absorbs the energy
of the electric waves, so that the fact was established that clear
sunlight and blue skies, though transparent to light, serve as a
fog to the powerful Hertzian waves of wireless telegraphy. For
that reason the transmission of messages is carried on with
greater facility on the shores of England and Newfoundland across
the North Atlantic than in the clearer atmosphere of lower
latitudes. But atmospheric conditions do not affect all forms of
waves the same, and long waves with small amplitudes are far less
subject to the effect of daylight than those of large amplitude
and short wave length, and generators and circuits were arranged
to produce the former. But the difficulty did not prove
insuperable, as Marconi found that increasing the energy of the
transmitting station during the daytime would more than make up
for the loss of range.
The experiments begun at Newfoundland were transferred to Nova
Scotia, and at Glace Bay in 1902 was established a station from
which messages were transmitted and experimental work carried on
until its work was temporarily interrupted by fire in 1909. Here
four wooden lattice towers, each 210 feet in height, were built at
the corner of a square 200 feet on a side, and a conical
arrangement of 400 copper wires supported on stays between the
tops of the towers and connected in the middle at the generating
station was built. Additional machinery was installed and at the
same time a station at Cape Cod for commercial work was built. In
December, 1902, regular communication was established between
Glace Bay and Poldhu, but it was only satisfactory from Canada to
England as the apparatus at the Poldhu station was less powerful
and efficient than that installed in Canada. The transmission of a
message from President Roosevelt to King Edward marked the
practical beginning of trans-Atlantic wireless telegraphy. By this
time a new device for the detection of messages was employed, as
the coherer we have described even in its improved forms was found
to possess its limitations of sensitiveness and did not respond
satisfactorily to long distance signals. A magnetic detector was
devised by Marconi while other inventors had contrived
electrolytic, mercurial, thermal, and other forms of detector,
used for the most part with a telephone receiver in order to
detect minute variations in the current caused by the reception of
the electro-magnetic waves. With one of Marconi's magnetic
detectors signals from Cape Cod were read at Poldhu.
In 1903 wireless telegraphy had reached such a development that
the transmission of news messages was attempted in March and April
of that year. But the service was suspended, owing to defects
which manifested themselves in the apparatus, and in the meantime
a new station in Ireland was erected. But there was no cessation
of the practical experiments carried on, and in 1903 the Cunard
steamship Lucania received, during her entire voyage across from
New York to Liverpool, news transmitted direct from shore to
shore. In the meantime intercommunication between ships had been
developed and the use of wireless in naval operations was
recognized as a necessity.
Various improvements from time to time were made in the aerial
wires, and in 1905 a number of horizontal wires were connected to
an aerial of the inverted cone type previously used. The
directional aerial with the horizontal wires was tried at Glace
Bay, and adopted for all the long distance stations, affording
considerable strengthening of the received signals at Poldhu
stations. Likewise improvements in the apparatus were effected at
both trans-Atlantic stations, consisting of the adoption of air
condensers composed of insulated metallic plate suspended in the
air, which were found much better than the condensers where glass
was previously used to separate the plates. For producing the
energy employed for transmitting the signals a high tension
continuous current dynamo is used. An oscillatory current of high
potential is produced in a circuit which consists of rapidly
rotating disks in connection with the dynamo and suitable
condensers.
The production of electric oscillations can be accomplished in
several ways and waves of the desired frequency and amplitude
produced. Thus in 1903 it was found by Poulsen, elaborating on a
principle first discovered by Duddell, that an oscillatory current
may be derived from an electric arc maintained under certain
conditions and that undamped high frequency waves so produced were
suitable for wireless telegraphy. This discovery was of
importance, as it was found that the waves so generated were
undamped, that is, capable of proceeding to their destination
without loss of amplitude. On this account they were especially
suitable for wireless telephony where they were early applied, as
it was found possible so to arrange a circuit with an ordinary
microphone transmitter that the amplitude of the waves would be
varied in harmony with the vibrations of the human voice. These
waves so modulated could be received by some form of sensitive
wave detector at a distant station and reproduced in the form of
sound with an ordinary telephone receiver. With undamped waves
from the arc and from special forms of generators wireless
telephony over distances as great as 200 miles has been
accomplished and over shorter distances, especially at sea and for
sea to shore, communication has found considerable application. It
is, however, an art that is just at the beginning of its
usefulness, standing in much the same relation to wireless
telegraphy that the ordinary telephone does to the familiar system
employing metallic conductors.
On the spark and arc systems various methods of wireless
telegraphy have been developed and improved so that Marconi no
longer has any monopoly of methods or instruments. Various
companies and government officials have devised or modified
systems so that to-day wireless is practically universal and is
governed by an international convention to which leading nations
of the world subscribe.
One of the recent features of wireless telegraphy of interest is
the success of various directional devices. As we have seen,
various schemes were tried by Marconi ranging from metallic
reflectors used by Hertz in his early experiments with the
electric waves to the more successful arrangement of aerial
conductors. In Europe Bellini and Tosi have developed a method for
obtaining directed aerial waves which promises to be of
considerable utility, enabling them to be projected in a single
direction just as a searchlight beam and thus restrict the number
of points at which the signals could be intercepted and read.
Likewise an arrangement was perfected which enabled a station to
determine the direction in which the waves were being projected
and consequently the bearing of another vessel or lighthouse or
other station. The fundamental principle was the arrangement of
the antennae, two triangular systems being provided on the same
mast, but in one the current is brought down in a perpendicular
direction. The action depends upon the difference of the current
in the two triangles.
Wireless telegraph apparatus is found installed in almost every
seagoing passenger vessel of large size engaged in regular
traffic, and as a means of safety as well as a convenience its
usefulness has been demonstrated. Thus on the North Atlantic the
largest liners are never out of touch with land on one side of the
ocean or the other, and news is supplied for daily papers which
are published on shipboard. Every ship in this part of the ocean
equipped with the Marconi system, for example, is in communication
on an average with four vessels supplied with instruments of the
same system every twenty-four hours. In case of danger or disaster
signals going out over the sea speedily can bring succour, as
clearly was demonstrated in the case of the collision between the
White Star steamship Republic and the steamship Florida on January
26, 1909. Here wireless danger messages were sent out as long as
the Republic was afloat and its wireless apparatus working. These
brought aid from various steamers in the vicinity and the
passengers were speedily transferred from the sinking Republic. On
April 15, 1912, the White Star liner Titanic, the largest ship
afloat, sank off Newfoundland, after colliding with an iceberg.
Wireless SOS calls for help brought several steamships to the
scene, and 703 persons from a total of 2,206, were rescued. On
October 9, 1913, the Uranium liner Volturno caught fire in mid-
ocean, and her wireless calls brought ten steamships to her aid,
which, despite a heavy sea, rescued 532 persons from a total of
657. Again, on November 14, 1913, the Spanish steamship Balmes
caught fire off Bermuda, and at her wireless call the Cunard liner
Pannonia saved all of her passengers--103. The Titanic horror led
the principal maritime nations to take immediate steps to perfect
their wireless systems, and the installation of apparatus and
operators soon became a prime requisite of the equipment of the
world's shipping. Wireless telegraphy has been developed to great
efficiency in all the leading navies, and powerful plants are
installed on all warships. The United States, Great Britain, and
Germany, most noticeably, have established shore stations, by
which they can "talk all around the world" from any ship or
station. In operation secrecy is most important. For in the navy
practically all important messages are sent in code or cipher
under all conditions while in commercial work the tapping of land
wires or the stealing of messages while illegal is physically
possible for the evil disposed yet has never proved in practice a
serious evil. The problem of interference, however, seems to have
been fairly solved by the large systems though the activity of
amateurs is often a serious disturbance for government and other
stations.
Despite the progress of wireless telegraphy it has not yet
supplanted the submarine cable and the land wire, and in
conservative opinion it will be many years before it will do so.
In fact, since Marconi's work there has been no diminution in the
number or amount of cables laid and the business handled, nor is
there prospect of such for years to come. While the cable has
answered admirably for telegraphic purposes yet for telephony over
considerable distances it has failed entirely so that wireless
telephony over oceans starts with a more than favorable outlook.
But wireless telegraphy to a large extent has made its own field
and here its work has been greatly successful. Thus when Peary's
message announcing his discovery of the North Pole came out of the
Frozen North, it was by way of the wireless station on the distant
Labrador coast that it reached an anxious and interested
civilization. It is this same wireless that watches the progress
of the fishing fleets at stations where commercial considerations
would render impossible the maintenance of a submarine cable. It
is the wireless telegraph that maintains communication in the
interior of Alaska and between islands in the Pacific and
elsewhere where conditions of development do not permit of the
more expensive installation of submarine cable or climatic or
other conditions render impossible overland lines. At sea its
advantages are obvious. Everywhere the ether responds to the
impulses of the crackling sparks, and even from the airship we
soon may expect wireless messages as the few untrodden regions of
our globe are explored.