Edison, in 1885, enabled the trains on a line of the Staten Island
Railroad to be kept in constant communication with a telegraphic wire,
suspended in the ordinary way beside the track. The roof of a car was of
insulated metal, and every tap of an operator's key within the walls
electrified the roof just long enough to induce a brief pulse through
the telegraphic circuit. In sending a message to the car this wire was,
moment by moment, electrified, inducing a response first in the car
roof, and next in the "sounder" beneath it. This remarkable apparatus,
afterward used on the Lehigh Valley Railroad, was discontinued from lack
of commercial support, although it would seem to be advantageous to
maintain such a service on other than commercial grounds. In case of
chance obstructions on the track, or other peril, to be able to
communicate at any moment with a train as it speeds along might mean
safety instead of disaster. The chief item in the cost of this system is
the large outlay for a special telegraphic wire.
The next electrician to employ induced currents in telegraphy was Mr.
(now Sir) William H. Preece, the engineer then at the head of the
British telegraph system. Let one example of his work be cited. In 1896
a cable was laid between Lavernock, near Cardiff, on the Bristol
Channel, and Flat Holme, an island three and a third miles off. As the
channel at this point is a much-frequented route and anchor ground, the
cable was broken again and again. As a substitute for it Mr. Preece, in
1898, strung wires along the opposite shores, and found that an electric
pulse sent through one wire instantly made itself heard in a telephone
connected with the other. It would seem that in this etheric form of
telegraphy the two opposite lines of wire must be each as long as the
distance which separates them; therefore, to communicate across the
English Channel from Dover to Calais would require a line along each
coast at least twenty miles in length. Where such lines exist for
ordinary telegraphy, they might easily lend themselves to the Preece
system of signalling in case a submarine cable were to part.
Marconi, adopting electrostatic instead of electro-magnetic waves, has
won striking results. Let us note the chief of his forerunners, as they
prepared the way for him. In 1864 Maxwell observed that electricity and
light have the same velocity, 186,400 miles a second, and he formulated
the theory that electricity propagates itself in waves which differ from
those of light only in being longer. This was proved to be true by
Hertz, who in 1888 showed that where alternating currents of very high
frequency were set up in an open circuit, the energy might be conveyed
entirely away from the circuit into the surrounding space as electric
waves. His detector was a nearly closed circle of wire, the ends being
soldered to metal balls almost in contact. With this simple apparatus he
demonstrated that electric waves move with the speed of light, and that
they can be reflected and refracted precisely as if they formed a
visible beam. At a certain intensity of strain the air insulation broke
down, and the air became a conductor. This phenomenon of passing quite
suddenly from a non-conductive to a conductive state is, as we shall
duly see, also to be noted when air or other gases are exposed to the X
ray.
Now for the effect of electric waves such as Hertz produced, when they
impinge upon substances reduced to powder or filings. Conductors, such
as the metals, are of inestimable service to the electrician; of equal
value are non-conductors, such as glass and gutta-percha, as they
strictly fence in an electric stream. A third and remarkable vista opens
to experiment when it deals with substances which, in their normal
state, are non-conductive, but which, agitated by an electric wave,
instantly become conductive in a high degree. As long ago as 1866 Mr. S.
A. Varley noticed that black lead, reduced to a loose dust, effectually
intercepted a current from fifty Daniell cells, although the battery
poles were very near each other. When he increased the electric tension
four- to six-fold, the black-lead particles at once compacted themselves
so as to form a bridge of excellent conductivity. On this principle he
invented a lightning-protector for electrical instruments, the incoming
flash causing a tiny heap of carbon dust to provide it with a path
through which it could safely pass to the earth. Professor Temistocle
Calzecchi Onesti of Fermo, in 1885, in an independent series of
researches, discovered that a mass of powdered copper is a non-conductor
until an electric wave beats upon it; then, in an instant, the mass
resolves itself into a conductor almost as efficient as if it were a
stout, unbroken wire. Professor Edouard Branly of Paris, in 1891, on
this principle devised a coherer, which passed from resistance to
invitation when subjected to an electric impulse from afar. He enhanced
the value of his device by the vital discovery that the conductivity
bestowed upon filings by electric discharges could be destroyed by
simply shaking or tapping them apart.
In a homely way the principle of the coherer is often illustrated in
ordinary telegraphic practice. An operator notices that his instrument
is not working well, and he suspects that at some point in his circuit
there is a defective contact. A little dirt, or oxide, or dampness, has
come in between two metallic surfaces; to be sure, they still touch each
other, but not in the firm and perfect way demanded for his work.
Accordingly he sends a powerful current abruptly into the line, which
clears its path thoroughly, brushes aside dirt, oxide, or moisture, and
the circuit once more is as it should be. In all likelihood, the coherer
is acted upon in the same way. Among the physicists who studied it in
its original form was Dr. Oliver J. Lodge. He improved it so much that,
in 1894, at the Royal Institution in London, he was able to show it as
an electric eye that registered the impact of invisible rays at a
distance of more than forty yards. He made bold to say that this
distance might be raised to half a mile.
As early as 1879 Professor D. E. Hughes began a series of experiments in
wireless telegraphy, on much the lines which in other hands have now
reached commercial as well as scientific success. Professor Hughes was
the inventor of the microphone, and that instrument, he declared,
affords an unrivalled means of receiving wireless messages, since it
requires no tapping to restore its non-conductivity. In his researches
this investigator was convinced that his signals were propagated, not by
electro-magnetic induction, but by aerial electric waves spreading out
from an electric spark. Early in 1880 he showed his apparatus to
Professor Stokes, who observed its operation carefully. His dictum was
that he saw nothing which could not be explained by known
electro-magnetic effects. This erroneous judgment so discouraged
Professor Hughes that he desisted from following up his experiments, and
thus, in all probability, the birth of the wireless telegraph was for
several years delayed.[3]
[Illustration: Fig. 71.--Marconi coherer, enlarged view]
The coherer, as improved by Marconi, is a glass tube about one and
one-half inches long and about one-twelfth of an inch in internal
diameter. The electrodes are inserted in this tube so as almost to
touch; between them is about one-thirtieth of an inch filled with a
pinch of the responsive mixture which forms the pivot of the whole
contrivance. This mixture is 90 per cent. nickel filings, 10 per cent.
hard silver filings, and a mere trace of mercury; the tube is exhausted
of air to within one ten-thousandth part (Fig. 71). How does this trifle
of metallic dust manage loudly to utter its signals through a
telegraphic sounder, or forcibly indent them upon a moving strip of
paper? Not directly, but indirectly, as the very last refinement of
initiation. Let us imagine an ordinary telegraphic battery strong enough
loudly to tick out a message. Be it ever so strong it remains silent
until its circuit is completed, and for that completion the merest touch
suffices. Now the thread of dust in the coherer forms part of such a
telegraphic circuit: as loose dust it is an effectual bar and obstacle,
under the influence of electric waves from afar it changes instantly to
a coherent metallic link which at once completes the circuit and
delivers the message.
An electric impulse, almost too attenuated for computation, is here able
to effect such a change in a pinch of dust that it becomes a free avenue
instead of a barricade. Through that avenue a powerful blow from a local
store of energy makes itself heard and felt. No device of the trigger
class is comparable with this in delicacy. An instant after a signal has
taken its way through the coherer a small hammer strikes the tiny tube,
jarring its particles asunder, so that they resume their normal state of
high resistance. We may well be astonished at the sensitiveness of the
metallic filings to an electric wave originating many miles away, but
let us remember how clearly the eye can see a bright lamp at the same
distance as it sheds a sister beam. Thus far no substance has been
discovered with a mechanical responsiveness to so feeble a ray of light;
in the world of nature and art the coherer stands alone. The electric
waves employed by Marconi are about four feet long, or have a frequency
of about 250,000,000 per second. Such undulations pass readily through
brick or stone walls, through common roofs and floors--indeed, through
all substances which are non-conductive to electric waves of ordinary
length. Were the energy of a Marconi sending-instrument applied to an
arc-lamp, it would generate a beam of a thousand candle-power. We have
thus a means of comparing the sensitiveness of the retina to light with
the responsiveness of the Marconi coherer to electric waves, after both
radiations have undergone a journey of miles.
An essential feature of this method of etheric telegraphy, due to
Marconi himself, is the suspension of a perpendicular wire at each
terminus, its length twenty feet for stations a mile apart, forty feet
for four miles, and so on, the telegraphic distance increasing as the
square of the length of suspended wire. In the Kingstown regatta, July,
1898, Marconi sent from a yacht under full steam a report to the shore
without the loss of a moment from start to finish. This feat was
repeated during the protracted contest between the _Columbia_ and the
_Shamrock_ yachts in New York Bay, October, 1899. On March 28, 1899,
Marconi signals put Wimereux, two miles north of Boulogne, in
communication with the South Foreland Lighthouse, thirty-two miles
off.[4] In August, 1899, during the manoeuvres of the British navy,
similar messages were sent as far as eighty miles. It was clearly
demonstrated that a new power had been placed in the hands of a naval
commander. "A touch on a button in a flagship is all that is now needed
to initiate every tactical evolution in a fleet, and insure an almost
automatic precision in the resulting movements of the ships. The
flashing lantern is superseded at night, flags and the semaphore by day,
or, if these are retained, it is for services purely auxiliary. The
hideous and bewildering shrieks of the steam-siren need no longer be
heard in a fog, and the uncertain system of gun signals will soon become
a thing of the past." The interest of the naval and military strategist
in the Marconi apparatus extends far beyond its communication of
intelligence. Any electrical appliance whatever may be set in motion by
the same wave that actuates a telegraphic sounder. A fuse may be
ignited, or a motor started and directed, by apparatus connected with
the coherer, for all its minuteness. Mr. Walter Jamieson and Mr. John
Trotter have devised means for the direction of torpedoes by ether
waves, such as those set at work in the wireless telegraph. Two rods
projecting above the surface of the water receive the waves, and are in
circuit with a coherer and a relay. At the will of the distant operator
a hollow wire coil bearing a current draws in an iron core either to the
right or to the left, moving the helm accordingly.
As the news of the success of the Marconi telegraph made its way to the
London Stock Exchange there was a fall in the shares of cable companies.
The fear of rivalry from the new invention was baseless. As but fifteen
words a minute are transmissible by the Marconi system, it evidently
does not compete with a cable, such as that between France and England,
which can transmit 2,500 words a minute without difficulty. The Marconi
telegraph comes less as a competitor to old systems than as a mode of
communication which creates a field of its own. We have seen what it may
accomplish in war, far outdoing any feat possible to other apparatus,
acoustic, luminous, or electrical. In quite as striking fashion does it
break new ground in the service of commerce and trade. It enables
lighthouses continually to spell their names, so that receivers aboard
ship may give the steersmen their bearings even in storm and fog. In the
crowded condition of the steamship "lanes" which cross the Atlantic, a
priceless security against collision is afforded the man at the helm.
On November 15, 1899, Marconi telegraphed from the American liner _St.
Paul_ to the Needles, sixty-six nautical miles away. On December 11 and
12, 1901, he received wireless signals near St. John's, Newfoundland,
sent from Poldhu, Cornwall, England, or a distance of 1,800 miles,--a
feat which astonished the world. In many cases the telegraphic business
to an island is too small to warrant the laying of a cable; hence we
find that Trinidad and Tobago are to be joined by the wireless system,
as also five islands of the Hawaiian group, eight to sixty-one miles
apart.
A weak point in the first Marconi apparatus was that anybody within the
working radius of the sending-instrument could read its messages. To
modify this objection secret codes were at times employed, as in
commerce and diplomacy. A complete deliverance from this difficulty is
promised in attuning a transmitter and a receiver to the same note, so
that one receiver, and no other, shall respond to a particular frequency
of impulses. The experiments which indicate success in this vital
particular have been conducted by Professor Lodge.
When electricians, twenty years ago, committed energy to a wire and thus
enabled it to go round a corner, they felt that they had done well. The
Hertz waves sent abroad by Marconi ask no wire, as they find their way,
not round a corner, but through a corner. On May 1, 1899, a party of
French officers on board the _Ibis_ at Sangatte, near Calais, spoke to
Wimereux by means of a Marconi apparatus, with Cape Grisnez, a lofty
promontory, intervening. In ascertaining how much the earth and the sea
may obstruct the waves of Hertz there is a broad and fruitful field for
investigation. "It may be," says Professor John Trowbridge, "that such
long electrical waves roll around the surface of such obstructions very
much as waves of sound and of water would do."
[Illustration: Fig. 73--Discontinuous electric waves]
[Illustration: Fig. 74--Wehnelt interrupter]
It is singular how discoveries sometimes arrive abreast of each other so
as to render mutual aid, or supply a pressing want almost as soon as it
is felt. The coherer in its present form is actuated by waves of
comparatively low frequency, which rise from zero to full height in
extremely brief periods, and are separated by periods decidedly longer
(Fig. 73). What is needed is a plan by which the waves may flow either
continuously or so near together that they may lend themselves to
attuning. Dr. Wehnelt, by an extraordinary discovery, may, in all
likelihood, provide the lacking device in the form of his interrupter,
which breaks an electric circuit as often as two thousand times a
second. The means for this amazing performance are simplicity itself
(Fig. 74). A jar, _a_, containing a solution of sulphuric acid has two
electrodes immersed in it; one of them is a lead plate of large surface,
_b_; the other is a small platinum wire which protrudes from a glass
tube, _d_. A current passing through the cell between the two metals at
_c_ is interrupted, in ordinary cases five hundred times a second, and
in extreme cases four times as often, by bubbles of gas given off from
the wire instant by instant.
FOOTNOTES:
[3] "History of the Wireless Telegraph," by J. J. Fahie. Edinburgh and
London, William Blackwood & Sons; New York, Dodd, Mead & Co., 1899. This
work is full of interesting detail, well illustrated.
[4] The value of wireless telegraphy in relation to disasters at sea was
proved in a remarkable way yesterday morning. While the Channel was
enveloped in a dense fog, which had lasted throughout the greater part
of the night, the East Goodwin Lightship had a very narrow escape from
sinking at her moorings by being run into by the steamship _R. F.
Matthews_, 1,964 tons gross burden, of London, outward bound from the
Thames. The East Goodwin Lightship is one of four such vessels marking
the Goodwin Sands, and, curiously enough, it happens to be the one ship
which has been fitted out with Signor Marconi's installation for
wireless telegraphy. The vessel was moored about twelve miles to the
northeast of the South Foreland Lighthouse (where there is another
wireless-telegraphy installation), and she is about ten miles from the
shore, being directly opposite Deal. The information regarding the
collision was at once communicated by wireless telegraphy from the
disabled lightship to the South Foreland Lighthouse, where Mr. Bullock,
assistant to Signor Marconi, received the following message: "We have
just been run into by the steamer _R. F. Matthews_ of London. Steamship
is standing by us. Our bows very badly damaged." Mr. Bullock immediately
forwarded this information to the Trinity House authorities at
Ramsgate.--_Times_, April 29, 1899.
ELECTRICITY, WHAT ITS MASTERY MEANS: WITH A REVIEW AND A PROSPECT
GEORGE ILES
[From "Flame, Electricity and the Camera," copyright by Doubleday,
Page & Co., New York.]
With the mastery of electricity man enters upon his first real
sovereignty of nature. As we hear the whirr of the dynamo or listen at
the telephone, as we turn the button of an incandescent lamp or travel
in an electromobile, we are partakers in a revolution more swift and
profound than has ever before been enacted upon earth. Until the
nineteenth century fire was justly accounted the most useful and
versatile servant of man. To-day electricity is doing all that fire ever
did, and doing it better, while it accomplishes uncounted tasks far
beyond the reach of flame, however ingeniously applied. We may thus
observe under our eyes just such an impetus to human intelligence and
power as when fire was first subdued to the purposes of man, with the
immense advantage that, whereas the subjugation of fire demanded ages of
weary and uncertain experiment, the mastery of electricity is, for the
most part, the assured work of the nineteenth century, and, in truth,
very largely of its last three decades. The triumphs of the electrician
are of absorbing interest in themselves, they bear a higher significance
to the student of man as a creature who has gradually come to be what he
is. In tracing the new horizons won by electric science and art, a beam
of light falls on the long and tortuous paths by which man rose to his
supremacy long before the drama of human life had been chronicled or
sung.
Of the strides taken by humanity on its way to the summit of terrestrial
life, there are but four worthy of mention as preparing the way for the
victories of the electrician--the attainment of the upright attitude,
the intentional kindling of fire, the maturing of emotional cries to
articulate speech, and the invention of written symbols for speech. As
we examine electricity in its fruitage we shall find that it bears the
unfailing mark of every other decisive factor of human advance: its
mastery is no mere addition to the resources of the race, but a
multiplier of them. The case is not as when an explorer discovers a
plant hitherto unknown, such as Indian corn, which takes its place
beside rice and wheat as a new food, and so measures a service which
ends there. Nor is it as when a prospector comes upon a new metal, such
as nickel, with the sole effect of increasing the variety of materials
from which a smith may fashion a hammer or a blade. Almost infinitely
higher is the benefit wrought when energy in its most useful phase is,
for the first time, subjected to the will of man, with dawning knowledge
of its unapproachable powers. It begins at once to marry the resources
of the mechanic and the chemist, the engineer and the artist, with issue
attested by all its own fertility, while its rays reveal province after
province undreamed of, and indeed unexisting, before its advent.
Every other primal gift of man rises to a new height at the bidding of
the electrician. All the deftness and skill that have followed from the
upright attitude, in its creation of the human hand, have been brought
to a new edge and a broader range through electric art. Between the uses
of flame and electricity have sprung up alliances which have created new
wealth for the miner and the metal-worker, the manufacturer and the
shipmaster, with new insights for the man of research. Articulate speech
borne on electric waves makes itself heard half-way across America, and
words reduced to the symbols of symbols--expressed in the perforations
of a strip of paper--take flight through a telegraph wire at twenty-fold
the pace of speech. Because the latest leap in knowledge and faculty has
been won by the electrician, he has widened the scientific outlook
vastly more than any explorer who went before. Beyond any predecessor,
he began with a better equipment and a larger capital to prove the
gainfulness which ever attends the exploiting a supreme agent of
discovery.
As we trace a few of the unending interlacements of electrical science
and art with other sciences and arts, and study their mutually
stimulating effects, we shall be reminded of a series of permutations
where the latest of the factors, because latest, multiplies all prior
factors in an unexampled degree.[5] We shall find reason to believe that
this is not merely a suggestive analogy, but really true as a tendency,
not only with regard to man's gains by the conquest of electricity, but
also with respect to every other signal victory which has brought him to
his present pinnacle of discernment and rule. If this permutative
principle in former advances lay undetected, it stands forth clearly in
that latest accession to skill and interpretation which has been ushered
in by Franklin and Volta, Faraday and Henry.
Although of much less moment than the triumphs of the electrician, the
discovery of photography ranks second in importance among the scientific
feats of the nineteenth century. The camera is an artificial eye with
almost every power of the human retina, and with many that are denied
to vision--however ingeniously fortified by the lens-maker. A brief
outline of photographic history will show a parallel to the permutative
impulse so conspicuous in the progress of electricity. At the points
where the electrician and the photographer collaborate we shall note
achievements such as only the loftiest primal powers may evoke.