been completed at the Gutta Percha works as described, a telegraphic
line was thereby produced which, without further addition of material or
substance, beyond that of copper and gutta percha, proportionable to any
required increase in its length, would be perfect as an electrical
communicator through the longest distances and in the deepest water, in
which element moreover it appears to be chemically indestructible, if
the experience of some fourteen years may be taken as evidence. At this
point, however, the final form to be assumed by the deep-sea Cable was
subject to important mechanical considerations, which came into play
across the path of those purely electrical; and upon the manner in which
these considerations are met and dealt with, depend, not merely the
primarily successful submersion, but the ultimate durability and
commercial value of deep-sea Cables.
The problem in the case of the Atlantic Telegraph enterprise may be thus
stated. Given a submarine telegraph core like that already described,
constructed on the best known principles and perfect as to its
electrical conductivity and insulation--it is required to lower the same
through the sea to a maximum depth of two and a-half miles, so as not
merely not to allow the insulating medium to be torn or strained, but so
as not even to bring its normal elasticity into play against the more
tensile but perfectly inelastic material of the conductor. For if the
core were lowered into very deep water like that referred to without
further protection, even supposing it to escape actual fracture by the
adoption of extraordinary precaution and by the aid of fine weather, it
is evident that whenever, as would be highly probable, either in the act
of paying out, during the lifting or manœuvring of the ship, or even
from the effects of its own weight, the gutta percha sheath became
extended to the limit of its elasticity, the copper in the centre would
be stretched to a corresponding extent, and, the tension being removed,
the gutta percha in returning to its original length would pull back the
now elongated copper, which thenceforward would in every such case
“buckle up,” and exert a constant lateral thrust against the gutta
percha; ending, probably, in its ultimate escape to the outside, and the
consequent destruction of the core as an electrical agent. Moreover, in
the event of an electrical fault being discovered in any submerged
portion of the Cable during the process of “paying-out” in deep water,
it is of paramount importance towards its recovery and repair, that the
engineer should have such an assurance in the quality and strength of
his materials as will enable him confidently to exert a known force in
hauling back the injured part, without apprehension of damage to the
vital portion of the Cable.
The solution of this question must therefore be found in adding
mechanical strength externally to the core, by surrounding it with such
materials and in such a manner as to relieve it from all that strain
which it will unavoidably meet in depositing it in its required
position. In the case of the original Atlantic Cable this was attempted
by first surrounding the core with tarred hemp, which in its turn was
enveloped spirally by eighteen strands of iron wire; each strand
consisting of seven No. 22½ gauge wires. The entire weight of the
Cable so formed was, in air 20 cwt. per knot, and in water 13·3 per
knot. Being capable of bearing its own weight in about five miles
perpendicular depth of water, and the greatest depth on the route being
two-and a half miles, its strength was calculated at about as much again
as was absolutely requisite for the work. This was thought at the time
to be a sufficient margin, and certainly in 1858, owing to the greatly
improved machinery employed, this Cable was payed-out with great
facility and without undue strain, although portions of it had been lost
by breaking during several previous attempts in the same summer.
Subsequent investigation and experience, however, led to the conclusion,
that in respect, not only to its mechanical properties, but especially
with regard to its relative specific gravity, and to other points in its
construction, the Cable of 1858 was very imperfect; and, with a view to
ensure every practicable improvement in the structure of their new line,
the promoters of the undertaking, so soon as they found themselves in
funds, during 1863, issued advertisements with a view to stimulate
inquiry into the subject, inviting tenders for Cables suitable for the
proposed work. The specimens that were sent in, as the result of this
public appeal, were submitted to the scientific advisers of the Company,
who, after careful experiments with all the specimens, unanimously
recommended the Atlantic Company to adopt the principle of the Cable
proposed by Glass, Elliot, & Co., whose experience and success in this
description of work are well known. The Committee, however, stipulated
that they should settle the actual material of which the Cable was to be
ultimately composed, and that these should be carefully and separately
experimented on before finally deciding upon it; and in consequence of
this stipulation upwards of one hundred and twenty different specimens,
being chiefly variations of the principle adopted by the Committee, were
manufactured and subjected to very severe experiment, as were also the
various descriptions and quantities of iron, hemp, and Manilla proposed
as components of these respective Cables. The result of it all was that
the Committee recommended the Cable that was adopted as being, in their
opinion, “the one most calculated to insure success in the present state
of our experimental knowledge respecting deep-sea Cables,” taking care
at the same time, by enforcing a stringent specification and constant
supervision, to guard against any possible laxity in the details of its
construction. The Cable so decided on weighed 35¾ cwt. per knot in
air, but in water it did not exceed 14 cwt., being only a fraction
heavier in that medium than the old Cable, though bearing more than
twice the strain--the breaking strain of the new Cable being 7 tons 15
cwt. In water it was capable of bearing eleven miles of its own length
perpendicularly suspended, and consequently had a margin of strength of
more than four and a-half times that which was absolutely requisite for
the deepest water. The core having been received from the gutta percha
works, and carefully tested to note its electrical condition, was first
taken to receive its padding of jute yarn, whereby the gutta percha
would be protected against any pressure from the external iron sheath,
which latter succeeded the jute. On former occasions this padding of
jute had been saturated in a mixture of tar before being applied to the
gutta percha; but experience had shown that this proceeding might lead
to serious fallacies as to the electrical state of the core, cases
having been repeatedly found where faults existed in the core
itself--amounting to an almost total loss of insulation--which, however,
were only discovered after being submerged and worked through, owing to
the partial insulation conferred for a time upon the bad place by means
of the tarred wrapping. The Atlantic core, therefore, was wrapped with
jute which had been simply tanned in a solution of catechu, in order to
preserve it from decay, and as fast as the wrapping proceeded the
wrapped core was coiled into water, in which, not only at this stage,
but ever afterwards until finally deposited in the sea, the Cable,
complete or incomplete, was stored, and the water being able to freely
pass through the tarred jute to the core, the least loss of insulation
was at once apparent by the facility offered by the water to conduct
away to earth the whole or a portion of the testing current.
The iron wire with which the jute cover was surrounded was specially
prepared for this purpose, and is termed by the makers (Messrs. Webster
& Horsfall) “Homogeneous Iron.” It was manufactured and rolled into rods
at their works at Killamarsh, near Sheffield, and drawn at their wire
factory at Hay mills, near Birmingham. This wire approaches to steel in
regard to strength, but by some peculiarity in the mode of preparing it,
is deprived entirely of that springiness which prohibits altogether the
use of steel as a covering for the outsides of submarine cables. Ten
wires were laid spirally round the core, and each of these wires was of
No. 13 gauge, and was under contract to bear a strain of 850 to 1,100
lb., with an elongation of half an inch in every fifty inches within
those breaking limits. The Cable, as completed and surrounded by these
wires, had not the slightest tendency to spring, as would be the case if
the metal were hard steel, and could be handled with great facility.
Before, however, these ten wires surrounded the core, each separate wire
had to be itself covered with a jacket of tarred Manilla yarn, the
object of which is at once to protect the iron from rust and to lighten
the specific gravity of the mass, while adding also in some degree to
the strength of the external portion of the Cable. The wire was drawn
horizontally forward over a drum through a hollow cylinder, on the
outside of which bobbins filled with Manilla yarn revolved vertically,
and the yarns from these bobbins, being made to converge around the wire
as it issued from the end of the cylinder, were thus spun tightly round
the former. These Manilla-covered wires being wound upon large drums
ready for use, the core, which we left some time back surrounded with
jute, was passed round several sheaves, which conducted it below the
floor of the factory, from whence it was drawn up again through a hole
in the centre of a circular table, around the circumference of which
were ten receptacles for ten drums, containing the Manilla-covered wire.
Between these drums massive iron rods, fastened to the circumference of
the table, rose, and converged around a small hollow cone of iron
through the upper flooring of the factory, at a height of 12 or 14 feet
above the table. The jute-covered core was pulled up vertically, and
passed on straight through the hollow interior of the cone already
mentioned, which latter formed the apex of the converging rods. This
done, the ten wires from the ten drums were drawn up over the outside of
the same cone, and as they rose beyond it converged around the core,
which latter, being free from the revolving part of the machinery, was
simply drawn out; while the circular table being now set revolving by
steam power, the ten wires from the drums were spun in a spiral around
the core, thus completing the Cable, which was hauled out of the factory
by the hands of men, who at the same time coiled it into large iron
tanks, where it was covered with water, and was daily subjected to the
most careful electrical tests, both by the very experienced staff of the
contractors and by the agents of the Atlantic Telegraph Company.
The distance from the western coast of Ireland to the spot in Trinity
Bay, Newfoundland, selected as the landing-place for the Cable, was a
little over 1,600 nautical miles, and the length of Cable contracted
for, to cover this distance, including the “slack,” was 2,300 knots,
which left a margin of 700 knots, to cover the inequalities of the
sea-bed, and to allow for contingencies. On the first occasion 2,500
statute miles were taken to sea, the distance to the Newfoundland
terminus on that occasion being 1,640 nautical miles; and, after losing
385 miles in 1857, and setting apart a further quantity for experiments
upon paying-out machinery, sufficient new Cable was manufactured to
enable the Niagara and Agamemnon to sail in 1858 with an aggregate of
2,963 statute miles on board the two ships, of which about 450 statute
miles were lost in the two first attempts of that year, and 2,110 miles
were finally laid and worked through.
The greatly increased weight and size of the Cable would have made the
question of stowage a very embarrassing one had it not been for the
existence of the Great Eastern steamship, there being no two ordinary
ships afloat that would be capable of containing, in a form convenient
for paying-out, the great bulk presented by 2,300 miles of a Cable of
such dimensions. This bulk, and the now acknowledged necessity for
keeping Cables continuously in water, made their influence to be felt in
a very expensive manner to the Company and to the contractors throughout
the progress of the work, even at this early stage. The works at Morden
Wharf had to be to a very large extent remodelled to meet these
contingencies. Eight enormous tanks, made of five-eighths and half-inch
plate iron, perfectly watertight, and very fine specimens of this
description of work, were erected on those premises, and these tanks
then received an aggregate of 80 miles of Cable per week. Four of the
tanks were circular in shape, and each contained 153 miles of cable,
being 34 ft. in diameter and 12 ft. deep. The other four were slightly
elliptical, being 36 ft. long by 27 ft. wide, and 12 ft. deep, and
contained each 140 miles. The contents of all these, as they became
full, were transferred to the Great Eastern at Sheerness, for which
service the Lords of the Admiralty granted the loan of two
sailing-ships, laid up in ordinary at Chatham, namely--the Amethyst and
the Iris.[4] These ships had to undergo very considerable alteration
to render them suitable for the work, portions of the main deck
having to be removed--fore and aft--to make room for watertight tanks,
which here, as elsewhere, were to be the medium for holding the Cable.
The dimensions of the two tanks on board the Amethyst were 29 ft.
diameter by 14 ft. 6 in. in depth, and each held 153 miles of Cable; of
those on the Iris, one was 29 ft. diameter and 14 ft. 6 in. deep, and
held 153 miles, and the other held 110 miles, and was 24 ft. wide, and
17 ft. deep.
[Illustration: F. Jones, lith from a drawing by R. Dudley
London, Day & Sons, Limited, Lith.
THE CABLE PASSED FROM THE WORKS INTO THE HULK LYING IN THE THAMES AT
GREENWICH.]
[Illustration: T. Picken, lith from a drawing by R. Dudley
London, Day & Sons, Limited, Lith.
THE OLD FRIGATE WITH HER FREIGHT OF CABLE ALONGSIDE THE “GREAT EASTERN”
AT SHEERNESS.]
The Great Eastern steamship was fitted up with three tanks to receive
the Cable, one situated in the forehold, one in the afterhold, and the
third nearly amidships. The bottoms and the first tier of plates were of
five-eighths iron, and each tank, when completed to this height, and
tested as to its tightness by filling it with water, and found or made
to be perfectly watertight, was let down from its temporary supports on
to a bed of Portland cement, three inches in thickness, and the building
up and riveting of the remaining tiers was continued. The beams beneath
each tank were shored up from the floor beneath it down to the kelson
with nine inches Baltic baulk timber, and it will give some idea of the
magnitude of the work to state that upwards of 300 loads of this
material were required for this purpose alone. The dimensions of the
fore tank were 51 ft. 6 in. diameter by 20 ft. 6 in. in depth, and its
capacity was for 693 miles of Cable. The middle tank was 58 ft. 6 in.
broad, and 20 ft. 6 in. deep, and held 899 miles of Cable, and the after
tank was 58 ft. wide and 20 ft. 6 in. deep, and contained 898 miles. The
three tanks were therefore capable of containing in all 2,490 miles of
the new Cable.
The experience gained on board the Agamemnon and Niagara, and the
practical knowledge obtained by the telegraphic engineers, were turned
to good account in erecting the new machinery on the deck of the Great
Eastern for paying-out the Cable.
Over the hold was a light wrought-iron V wheel, the speed of which was
regulated by a friction wheel on the same shaft. This was connected with
the paying-out machinery by a wrought-iron trough, in which, at
intervals, were smaller wrought-iron V wheels, and at the angles
vertical guide wheels. The paying-out machinery consisted of a series of
V wheels and jockey or riding wheels (six in number); upon the shafts of
the V wheels were friction wheels, with brake straps weighted by levers
and running in tanks filled with water: and upon the shafts of the
jockey wheels were also friction straps and levers, with weights to hold
the Cable and keep it taut round the drum. Immediately before the drum
was a small guide wheel, placed under an apparatus called the knife, for
keeping the first turn of the Cable on the drum from riding or getting
over another turn. The knives, of which there were two, could be removed
and adjusted with the greatest ease by slides similar to a slide-rest
of an ordinary turning-lathe. One knife only was used, the other being
kept ready to replace it if necessary. The drum, round which the Cable
passed, was 6 feet diameter and 1 foot broad, and upon the same shaft
were fixed two Appold’s brakes, running in tanks filled with water.
There was also a duplicate drum and pair of Appold’s brakes fitted in
position and ready for use in case of accident. Upon the overhanging
ends of the shafts of the drums driving pulleys were fitted, which could
be connected by a leather belt for the purpose of bringing into use the
duplicate brakes, if the working brakes should be out of order. Between
the duplicate drum and the stern wheel were placed the dynamometer and
intermediate wheels for indicating the strain upon the Cable. The
dynamometer wheel was placed midway between the two intermediate wheels,
and the strain was indicated by the rising or falling of the dynamometer
wheel on a graduated scale of cwts. attached to the guide rods of the
dynamometer slide. The stern wheel, over which the Cable passed when
leaving the ship, was a strong V wheel, supported on wrought-iron
girders overhanging the stern, and the Cable was protected from injury
by the flanges of this wheel by a bell-mouthed cast-iron shield
surrounding half its circumference.
Close to the dynamometer was placed an apparatus similar to a
double-purchase crab, or winch, fitted with two steering wheels, for
lifting the jockey or riding wheels with their weights and the weights
on the main brakes of the drum, as indications were shown upon the
dynamometer scale.
All the brake wheels ran in tanks supplied with water by pipes from the
paddle-box tanks of the ship.
The Cable passed over the wrought-iron V wheel over the tank along the
trough, between the V wheels and jockey wheels in a straight line; four
turns round the drum where the knife comes into action over the first
intermediate wheel, under the dynamometer wheel, and over the other
intermediate and stern wheels into the sea.
[Illustration: From a drawing by R. Dudley London, Day & Sons, Limited,
Lith.
PAYING-OUT MACHINERY.]
[Illustration: T. Picken, lith from a drawing by R. Dudley London, Day &
Sons, Limited, Lith.
COILING THE CABLE IN THE AFTER TANK ON BOARD THE GREAT EASTERN AT
SHEERNESS. VISIT OF H.R.H. THE PRINCE OF WALES ON MAY 24th.]
This dynamometer was only a heavy wheel resting on the rope, but fixed
in an upright frame, which allowed it to slide freely up and down, and
on this frame were marked the figures which showed exactly the strain in
pounds on the Cable. Thus, when the strain was low the Cable slackened,
and the dynamometer sunk low with it; when, on the contrary, the strain
was great, the Cable was drawn “taut,” and on it the dynamometer rose to
its full height. When it sunk too low, the Cable was generally running
away too fast, and the brakes had to be applied to check it; when, on
the contrary, it rose rapidly the tension was dangerous, and the brakes
had to be almost opened to relieve it. The simplicity of the apparatus
for opening and shutting the brakes was most beautiful. Opposite the
dynamometer was placed a tiller-wheel, and the man in charge of it
never let it go or slackened in his attention for an instant, but
watched the rise and fall of the dynamometer as a sailor at the wheel
watches his compass. A single movement of this wheel to the right put
the brakes on, a turn to the left opened them. A good and experienced
brakeman would generally contrive to avoid either extreme of a high or
low strain, though there were few duties connected with the laying of
submarine cables which were more anxious and more responsible while they
last, than those connected with the management of the brakes. The whole
machine worked beautifully, and with so little friction that when the
brakes were removed, a weight of 200 lb. was sufficient to draw the
Cable through it.
In order to guard against any possible sources of accident, every
preparation was made in case of the worst, and, in the event of very bad
weather, for cutting the Cable adrift and buoying it. For this purpose a
wire rope of great strength, and no less than five miles long, having a
distinctive mark at every 100 fathoms, was taken in the Great Eastern.
This, of course, was only carried in case of desperate eventualities
arising, and in the earnest hope that not an inch of it would ever be
required. If, as unfortunately happened, its services were wanted, the
Cable could be firmly made fast to its extremity, and so many hundred
fathoms of the wire rope, according to the depth of water the Cable was
in, measured out. To the other end of the rope an immense buoy was
attached, and the whole would then be cut adrift and left to itself till
better weather.
On the 24th of May, His Royal Highness the Prince of Wales, accompanied
by many distinguished personages, paid a long visit to the Great
Eastern, for the purpose of inspecting the arrangements made for laying
the Cable. His Royal Highness was received by Mr. Pender, the Chairman
of the Telegraph Construction Company; Mr. Glass, Managing Director; and
a large number of the electricians and officers connected with the
undertaking. After partaking of breakfast, the Prince visited each
portion of the ship, and witnessed the transmission of a message sent
through the coils, which then represented in length 1,395 nautical
miles. The signals transmitted were seven words, =“I WISH SUCCESS TO THE
ATLANTIC CABLE,”= and were received at the other end of the coils in the
course of a few seconds--a rate of speed which spoke hopefully of
success.
On Monday, the 29th of May, the last mile of this gigantic Cable was
completed at Glass, Elliot, & Co.’s works; an event celebrated in the
presence of all the eminent scientific men who had laboured so zealously
in the promotion of the undertaking at Greenwich. When the tinkling of
the bell gave notice that the machine was empty, and the last coil of
the Cable stowed away, the mighty work, the accomplishment of which was
their dream by night and their study by day, stood completed. For eight
long months the huge machines had been in a constant whirl,
manufacturing those twenty-three hundred nautical miles of Cable
destined to perform a mission so important, and yet it would be
difficult to point to a single hour during which they did not yield
something to cause care and anxiety.
On Wednesday, the 14th of June, the Amethyst completed her final visit,
and commenced to deliver the last instalment of the Cable to the Great
Eastern.
On the 24th the Great Eastern left the Medway for the Nore, carrying
7000 tons of Cable, 2000 tons of iron tanks, and 7000 tons of coal. At
the Nore she took in 1,500 additional tons of coal, which brought her
total dead-weight to 21,000 tons.
Mr. Gooch, M.P., Chairman of the Great Eastern Company and Director of
the Telegraph Construction and Maintenance Company; Mr. Barber (Great
Eastern), Mr. Cyrus Field, Captain Hamilton, Directors of the Atlantic
Telegraph Company; M. Jules Despescher; Mr. H. O’Neil, A.R.A.; Mr.
Brassey, Mr. Fairbairn, Mr. Dudley, the representatives of some of the
principal journals, and several visitors, went round in the vessel from
the Nore to Ireland.
The whole of the arrangements for paying-out and landing the Cable were
in charge of Mr. Canning, principal Engineer to the Telegraph
Construction and Maintenance Company, Mr. Clifford being in charge of
the machinery. These gentlemen were assisted by Mr. Temple, Mr. London,
and eight experienced engineers and mechanists. A corps of Cable layers
was furnished by the Telegraph Construction and Maintenance Company.