scientific mind of Dr. Gale, and applied by him to operate Mr. Morse's
machine at a distance.
Previous to my investigations the means of developing magnetism in soft
iron were imperfectly understood. The electro-magnet made by Sturgeon,
and copied by Dana, of New York, was an imperfect quantity magnet, the
feeble power of which was developed by a single battery. It was entirely
inapplicable to a long circuit with an intensity battery, and no person
possessing the requisite scientific knowledge, would have attempted to
use it in that connection after reading my paper.
In sending a message to a distance, two circuits are employed, the
first a long circuit through which the electricity is sent to the
distant station to bring into action the second, a short one, in which
is the local battery and magnet for working the machine. In order to
give projectile force sufficient to send the power to a distance, it is
necessary to use an intensity battery in the long circuit, and in
connection with this, at the distant station, a magnet surrounded with
many turns of one long wire must be employed to receive and multiply the
effect of the current enfeebled by its transmission through the long
conductor. In the local or short circuit either an intensity or a
quantity magnet may be employed. If the first be used, then with it a
compound battery will be required; and, therefore on account of the
increased resistance due to the greater quantity of acid, a less amount
of work will be performed by a given amount of material; and,
consequently, though this arrangement is practicable it is by no means
economical. In my original paper I state that the advantages of a
greater conducting power, from using several wires in the quantity
magnet, may, in a less degree, be obtained by substituting for them one
large wire; but in this case, on account of the greater obliquity of the
spires and other causes, the magnetic effect would be less. In
accordance with these principles, the receiving magnet, or that which is
introduced into the long circuit, consists of a horseshoe magnet
surrounded with many hundred turns of a single long wire, and is
operated with a battery of from twelve to twenty-four elements or more,
while in the local circuit it is customary to employ a battery of one or
two elements with a much thicker wire and fewer turns.
It will, I think, be evident to the impartial reader that these were
improvements in the electro-magnet, which first rendered it adequate to
the transmission of mechanical power to a distance; and had I omitted
all allusion to the telegraph in my paper, the conscientious historian
of science would have awarded me some credit, however small might have
been the advance which I made. Arago and Sturgeon, in the accounts of
their experiments, make no mention of the telegraph, and yet their names
always have been and will be associated with the invention. I briefly,
however, called attention to the fact of the applicability of my
experiments to the construction of the telegraph; but not being familiar
with the history of the attempts made in regard to this invention, I
called it "Barlow's project," while I ought to have stated that Mr.
Barlow's investigation merely tended to disprove the possibility of a
telegraph.
I did not refer exclusively to the needle telegraph when, in my paper, I
stated that the _magnetic_ action of a current from a trough is at least
not sensibly diminished by passing through a long wire. This is evident
from the fact that the immediate experiment from which this deduction
was made was by means of an electro-magnet and not by means of a needle
galvanometer.
[Illustration: Fig. 7]
At the conclusion of the series of experiments which I described in
_Silliman's Journal_, there were two applications of the electro-magnet
in my mind: one the production of a machine to be moved by
electro-magnetism, and the other the transmission of or calling into
action power at a distance. The first was carried into execution in the
construction of the machine described in _Silliman's Journal_, vol. xx,
1831, and for the purpose of experimenting in regard to the second, I
arranged around one of the upper rooms in the Albany Academy a wire of
more than a mile in length, through which I was enabled to make signals
by sounding a bell, (Fig. 7.) The mechanical arrangement for effecting
this object was simply a steel bar, permanently magnetized, of about ten
inches in length, supported on a pivot, and placed with its north end
between the two arms of a horseshoe magnet. When the latter was excited
by the current, the end of the bar thus placed was attracted by one arm
of the horseshoe, and repelled by the other, and was thus caused to move
in a horizontal plane and its further extremity to strike a bell
suitably adjusted.
I also devised a method of breaking a circuit, and thereby causing a
large weight to fall. It was intended to illustrate the practicability
of calling into action a great power at a distance capable of producing
mechanical effects; but as a description of this was not printed, I do
not place it in the same category with the experiments of which I
published an account, or the facts which could be immediately deduced
from my papers in _Silliman's Journal_.
From a careful investigation of the history of electro-magnetism in its
connection with the telegraph, the following facts may be established:
1. Previous to my investigations the means of developing magnetism in
soft iron were imperfectly understood, and the electro-magnet which then
existed was inapplicable to the transmission of power to a distance.
2. I was the first to prove by actual experiment that, in order to
develop magnetic power at a distance, a galvanic battery of intensity
must be employed to project the current through the long conductor, and
that a magnet surrounded by many turns of one long wire must be used to
receive this current.
3. I was the first actually to magnetize a piece of iron at a distance,
and to call attention to the fact of the applicability of my experiments
to the telegraph.
4. I was the first to actually sound a bell at a distance by means of
the electro-magnet.
5. The principles I had developed were applied by Dr. Gale to render
Morse's machine effective at a distance.
THE FIRST ATLANTIC CABLES
GEORGE ILES
[From "Flame, Electricity and the Camera," copyright Doubleday,
Page & Co., New York.]
Electric telegraphy on land has put a vast distance between itself and
the mechanical signalling of Chappe, just as the scope and availability
of the French invention are in high contrast with the rude signal fires
of the primitive savage. As the first land telegraphs joined village to
village, and city to city, the crossing of water came in as a minor
incident; the wires were readily committed to the bridges which spanned
streams of moderate width. Where a river or inlet was unbridged, or a
channel was too wide for the roadway of the engineer, the question
arose, May we lay an electric wire under water? With an ordinary land
line, air serves as so good a non-conductor and insulator that as a rule
cheap iron may be employed for the wire instead of expensive copper. In
the quest for non-conductors suitable for immersion in rivers, channels,
and the sea, obstacles of a stubborn kind were confronted. To overcome
them demanded new materials, more refined instruments, and a complete
revision of electrical philosophy.
As far back as 1795, Francisco Salva had recommended to the Academy of
Sciences, Barcelona, the covering of subaqueous wires by resin, which
is both impenetrable by water and a non-conductor of electricity.
Insulators, indeed, of one kind and another, were common enough, but
each of them was defective in some quality indispensable for success.
Neither glass nor porcelain is flexible, and therefore to lay a
continuous line of one or the other was out of the question. Resin and
pitch were even more faulty, because extremely brittle and friable. What
of such fibres as hemp or silk, if saturated with tar or some other good
non-conductor? For very short distances under still water they served
fairly well, but any exposure to a rocky beach with its chafing action,
any rub by a passing anchor, was fatal to them. What the copper wire
needed was a covering impervious to water, unchangeable in composition
by time, tough of texture, and non-conducting in the highest degree.
Fortunately all these properties are united in gutta-percha: they exist
in nothing else known to art. Gutta-percha is the hardened juice of a
large tree (_Isonandra gutta_) common in the Malay Archipelago; it is
tough and strong, easily moulded when moderately heated. In comparison
with copper it is but one 60,000,000,000,000,000,000th as conductive. As
without gutta-percha there could be no ocean telegraphy, it is worth
while recalling how it came within the purview of the electrical
engineer.
In 1843 Jose d'Almeida, a Portuguese engineer, presented to the Royal
Asiatic Society, London, the first specimens of gutta-percha brought to
Europe. A few months later, Dr. W. Montgomerie, a surgeon, gave other
specimens to the Society of Arts, of London, which exhibited them; but
it was four years before the chief characteristic of the gum was
recognized. In 1847 Mr. S. T. Armstrong of New York, during a visit to
London, inspected a pound or two of gutta-percha, and found it to be
twice as good a non-conductor as glass. The next year, through his
instrumentality, a cable covered with this new insulator was laid
between New York and Jersey City; its success prompted Mr Armstrong to
suggest that a similarly protected cable be submerged between America
and Europe. Eighteen years of untiring effort, impeded by the errors
inevitable to the pioneer, stood between the proposal and its
fulfilment. In 1848 the Messrs. Siemens laid under water in the port of
Kiel a wire covered with seamless gutta-percha, such as, beginning with
1847, they had employed for subterranean conductors. This particular
wire was not used for telegraphy, but formed part of a submarine-mine
system. In 1849 Mr. C. V. Walker laid an experimental line in the
English Channel; he proved the possibility of signalling for two miles
through a wire covered with gutta-percha, and so prepared the way for a
venture which joined the shores of France and England.
[Illustration: Fig. 58.--Calais-Dover cable, 1851]
In 1850 a cable twenty-five miles in length was laid from Dover to
Calais, only to prove worthless from faulty insulation and the lack of
armour against dragging anchors and fretting rocks. In 1851 the
experiment was repeated with success. The conductor now was not a single
wire of copper, but four wires, wound spirally, so as to combine
strength with flexibility; these were covered with gutta-percha and
surrounded with tarred hemp. As a means of imparting additional
strength, ten iron wires were wound round the hemp--a feature which has
been copied in every subsequent cable (Fig. 58). The engineers were fast
learning the rigorous conditions of submarine telegraphy; in its
essentials the Dover-Calais line continues to be the type of deep-sea
cables to-day. The success of the wire laid across the British Channel
incited other ventures of the kind. Many of them, through careless
construction or unskilful laying, were utter failures. At last, in 1855,
a submarine line 171 miles in length gave excellent service, as it
united Varna with Constantinople; this was the greatest length of
satisfactory cable until the submergence of an Atlantic line.
In 1854 Cyrus W. Field of New York opened a new chapter in electrical
enterprise as he resolved to lay a cable between Ireland and
Newfoundland, along the shortest line that joins Europe to America. He
chose Valentia and Heart's Content, a little more than 1,600 miles
apart, as his termini, and at once began to enlist the co-operation of
his friends. Although an unfaltering enthusiast when once his great idea
had possession of him, Mr. Field was a man of strong common sense. From
first to last he went upon well-ascertained facts; when he failed he did
so simply because other facts, which he could not possibly know, had to
be disclosed by costly experience. Messrs. Whitehouse and Bright,
electricians to his company, were instructed to begin a preliminary
series of experiments. They united a continuous stretch of wires laid
beneath land and water for a distance of 2,000 miles, and found that
through this extraordinary circuit they could transmit as many as four
signals per second. They inferred that an Atlantic cable would offer but
little more resistance, and would therefore be electrically workable and
commercially lucrative.
In 1857 a cable was forthwith manufactured, divided in halves, and
stowed in the holds of the _Niagara_ of the United States navy, and the
_Agamemnon_ of the British fleet. The _Niagara_ sailed from Ireland; the
sister ship proceeded to Newfoundland, and was to meet her in mid-ocean.
When the _Niagara_ had run out 335 miles of her cable it snapped under
a sudden increase of strain at the paying-out machinery; all attempts at
recovery were unavailing, and the work for that year was abandoned. The
next year it was resumed, a liberal supply of new cable having been
manufactured to replace the lost section, and to meet any fresh
emergency that might arise. A new plan of voyages was adopted: the
vessels now sailed together to mid-sea, uniting there both portions of
the cable; then one ship steamed off to Ireland, the other to the
Newfoundland coast. Both reached their destinations on the same day,
August 5, 1858, and, feeble and irregular though it was, an electric
pulse for the first time now bore a message from hemisphere to
hemisphere. After 732 despatches had passed through the wire it became
silent forever. In one of these despatches from London, the War Office
countermanded the departure of two regiments about to leave Canada for
England, which saved an outlay of about $250,000. This widely quoted
fact demonstrated with telling effect the value of cable telegraphy.
Now followed years of struggle which would have dismayed any less
resolute soul than Mr. Field. The Civil War had broken out, with its
perils to the Union, its alarms and anxieties for every American heart.
But while battleships and cruisers were patrolling the coast from Maine
to Florida, and regiments were marching through Washington on their way
to battle, there was no remission of effort on the part of the great
projector.
Indeed, in the misunderstandings which grew out of the war, and that at
one time threatened international conflict, he plainly saw how a cable
would have been a peace-maker. A single word of explanation through its
wire, and angry feelings on both sides of the ocean would have been
allayed at the time of the _Trent_ affair. In this conviction he was
confirmed by the English press; the London _Times_ said: "We nearly went
to war with America because we had no telegraph across the Atlantic." In
1859 the British government had appointed a committee of eminent
engineers to inquire into the feasibility of an Atlantic telegraph, with
a view to ascertaining what was wanting for success, and with the
intention of adding to its original aid in case the enterprise were
revived. In July, 1863, this committee presented a report entirely
favourable in its terms, affirming "that a well-insulated cable,
properly protected, of suitable specific gravity, made with care, tested
under water throughout its progress with the best-known apparatus, and
paid into the ocean with the most improved machinery, possesses every
prospect of not only being successfully laid in the first instance, but
may reasonably be relied upon to continue for many years in an efficient
state for the transmission of signals."
Taking his stand upon this endorsement, Mr. Field now addressed himself
to the task of raising the large sum needed to make and lay a new cable
which should be so much better than the old ones as to reward its owners
with triumph. He found his English friends willing to venture the
capital required, and without further delay the manufacture of a new
cable was taken in hand. In every detail the recommendations of the
Scientific Committee were carried out to the letter, so that the cable
of 1865 was incomparably superior to that of 1858. First, the central
copper wire, which was the nerve along which the lightning was to run,
was nearly three times larger than before. The old conductor was a
strand consisting of seven fine wires, six laid around one, and weighed
but 107 pounds to the mile. The new was composed of the same number of
wires, but weighed 300 pounds to the mile. It was made of the finest
copper obtainable.
To secure insulation, this conductor was first embedded in Chatterton's
compound, a preparation impervious to water, and then covered with four
layers of gutta-percha, which were laid on alternately with four thin
layers of Chatterton's compound. The old cable had but three coatings of
gutta-percha, with nothing between. Its entire insulation weighed but
261 pounds to the mile, while that of the new weighed 400 pounds.[1] The
exterior wires, ten in number, were of Bessemer steel, each separately
wound in pitch-soaked hemp yarn, the shore ends specially protected by
thirty-six wires girdling the whole. Here was a combination of the
tenacity of steel with much of the flexibility of rope. The insulation
of the copper was so excellent as to exceed by a hundredfold that of the
core of 1858--which, faulty though it was, had, nevertheless, sufficed
for signals. So much inconvenience and risk had been encountered in
dividing the task of cable-laying between two ships that this time it
was decided to charter a single vessel, the _Great Eastern_, which,
fortunately, was large enough to accommodate the cable in an unbroken
length. Foilhommerum Bay, about six miles from Valentia, was selected as
the new Irish terminus by the company. Although the most anxious care
was exercised in every detail, yet, when 1,186 miles had been laid, the
cable parted in 11,000 feet of water, and although thrice it was
grappled and brought toward the surface, thrice it slipped off the
grappling hooks and escaped to the ocean floor. Mr. Field was obliged to
return to England and face as best he might the men whose capital lay at
the bottom of the sea--perchance as worthless as so much Atlantic ooze.
With heroic persistence he argued that all difficulties would yield to a
renewed attack. There must be redoubled precautions and vigilance never
for a moment relaxed. Everything that deep-sea telegraphy has since
accomplished was at that moment daylight clear to his prophetic view.
Never has there been a more signal example of the power of enthusiasm to
stir cold-blooded men of business; never has there been a more striking
illustration of how much science may depend for success upon the
intelligence and the courage of capital. Electricians might have gone on
perfecting exquisite apparatus for ocean telegraphy, or indicated the
weak points in the comparatively rude machinery which made and laid the
cable, yet their exertions would have been wasted if men of wealth had
not responded to Mr. Field's renewed appeal for help. Thrice these men
had invested largely, and thrice disaster had pursued their ventures;
nevertheless they had faith surviving all misfortunes for a fourth
attempt.
In 1866 a new company was organized, for two objects: first, to recover
the cable lost the previous year and complete it to the American shore;
second, to lay another beside it in a parallel course. The _Great
Eastern_ was again put in commission, and remodelled in accordance with
the experience of her preceding voyage. This time the exterior wires of
the cable were of galvanized iron, the better to resist corrosion. The
paying-out machinery was reconstructed and greatly improved. On July 13,
1866, the huge steamer began running out her cable twenty-five miles
north of the line struck out during the expedition of 1865; she arrived
without mishap in Newfoundland on July 27, and electrical communication
was re-established between America and Europe. The steamer now returned
to the spot where she had lost the cable a few months before; after
eighteen days' search it was brought to the deck in good order. Union
was effected with the cable stowed in the tanks below, and the prow of
the vessel was once more turned to Newfoundland. On September 8th this
second cable was safely landed at Trinity Bay. Misfortunes now were at
an end; the courage of Mr. Field knew victory at last; the highest
honors of two continents were showered upon him.
'Tis not the grapes of Canaan that repay,
But the high faith that failed not by the way.
[Illustration: Fig. 59.--Commercial cable, 1894]
What at first was as much a daring adventure as a business enterprise
has now taken its place as a task no more out of the common than
building a steamship, or rearing a cantilever bridge. Given its price,
which will include too moderate a profit to betray any expectation of
failure, and a responsible firm will contract to lay a cable across the
Pacific itself. In the Atlantic lines the uniformly low temperature of
the ocean floor (about 4 deg. C.), and the great pressure of the
superincumbent sea, co-operate in effecting an enormous enhancement both
in the insulation and in the carrying capacity of the wire. As an
example of recent work in ocean telegraphy let us glance at the cable
laid in 1894, by the Commercial Cable Company of New York. It unites
Cape Canso, on the northeastern coast of Nova Scotia, to Waterville, on
the southwestern coast of Ireland. The central portion of this cable
much resembles that of its predecessor in 1866. Its exterior armour of
steel wires is much more elaborate. The first part of Fig. 59 shows the
details of manufacture: the central copper core is covered with
gutta-percha, then with jute, upon which the steel wires are spirally
wound, followed by a strong outer covering. For the greatest depths at
sea, type _A_ is employed for a total length of 1,420 miles; the
diameter of this part of the cable is seven-eighths of an inch. As the
water lessens in depth the sheathing increases in size until the
diameter of the cable becomes one and one-sixteenth inches for 152
miles, as type _B_. The cable now undergoes a third enlargement, and
then its fourth and last proportions are presented as it touches the
shore, for a distance of one and three-quarter miles, where type _C_ has
a diameter of two and one-half inches. The weights of material used in
this cable are: copper wire, 495 tons; gutta-percha, 315 tons; jute
yarn, 575 tons; steel wire, 3,000 tons; compound and tar, 1,075 tons;
total, 5,460 tons. The telegraph-ship _Faraday_, specially designed for
cable-laying, accomplished the work without mishap.
Electrical science owes much to the Atlantic cables, in particular to
the first of them. At the very beginning it banished the idea that
electricity as it passes through metallic conductors has anything like
its velocity through free space. It was soon found, as Professor
Mendenhall says, "that it is no more correct to assign a definite
velocity to electricity than to a river. As the rate of flow of a river
is determined by the character of its bed, its gradient, and other
circumstances, so the velocity of an electric current is found to depend
on the conditions under which the flow takes place."[2] Mile for mile
the original Atlantic cable had twenty times the retarding effect of a
good aerial line; the best recent cables reduce this figure by nearly
one-half.