which Robert Wentworth had brought down with him. He was standing by
her side, listening attentively and critically, stopping her every
now and then, to make her go over the ground again, frankly pointing
out defects of style or what not, as his habit was with all we did. A
glorious July evening.
The world's comforter, with weary gait,
His day's hot task has ended in the west.
I was sitting at the open window, my eyes turned towards the hill-side,
bathed in the glory of departing day, my mind attuned to Lilian's
music, and reflecting the _couleur de rose_ of the scene outside. I
was indulging myself with a peep into dream-land, though a little
doubtfully, and somewhat as an interloper, liable at any time to be
warned off the enchanted ground, which, in my self-consciousness, I
told myself youth alone has a right to enter, when my attention was
attracted towards Becky, standing at the door and beckoning me out of
the room.
'A letter for you, Miss; just come by the evening post,' she whispered,
slipping it into my hand when I joined her outside. I noticed that
Becky always called me aside to give me the foreign letters now; as
though she intuitively felt that I should prefer to receive them when
alone.
I thanked her with a look; and hastily catching up my garden-hat,
slipped by the window and out at the gate, unobserved; then hurried
down the lane to read my precious letter at the stile, in the red glory
of the sunset.
A letter from Philip--and what a letter!--'My wife--my dear wife. At
last I am setting my face homewards'----
Ah, well; I think I will tell the rest in my own words. I have been
chary of quoting Philip's letters hitherto, and they shall be sacred
still. Enough for me to say that his affairs were definitely settled at
last. He loved me--he _did_ love me--in a way which it made me humble
to think of; humble, and proud, and glad, with all a woman's strength
and depth. Ah! Philip, for once I was satisfied for your sake; it _was_
something stronger, and deeper, and more enduring than a girl's love
awaiting you!
How tenderly he wrote about the pain which the long waiting had cost
him! How tenderly he dwelt upon what he termed my unselfishness in
acceding to the delay! How rejoiced he seemed to be at last able to
claim me--'_me_,' I repeated, nodding pleasantly at a wild rose peeping
round the hedge. 'You wouldn't imagine it, I daresay, but it is true,
nevertheless.'
Philip had never written like this before; never until now had it
been so evident how much the long waiting had cost him. Whilst I had
sometimes tormented myself with fears lest the separation should at
length have become a matter of course to him, he had been silently
rebelling. I could only judge how much by the sudden revulsion--the
contrast in his tone now that the waiting was at an end.
He had made enough to satisfy us two, without any more
'money-grubbing,' as he termed it. He would have nearly two thousand
a year when he had retired from the partnership and all was settled.
We could now live the life we had dreamt of in the old times, with
the gratification of knowing that we had earned it. Any time after
the middle of next month he might be expected. 'And you must amuse
yourself in the meantime in deciding where we are to pitch our tent.
Look about for a house after your own heart for us to settle down in;'
and so forth, and so forth. Was ever woman so blessed! My whole being
steeped in happiness, I clasped my hands upon the top bar of the stile
and tried to offer up a thanksgiving. What had I done to deserve all
the happiness showered upon me? What was I that I should be so blessed?
But mental prayer was not enough. There was the irresistible desire to
_give_ as well as receive, which is experienced in all seasons of great
joy. Who can love one truly without being in more sympathy with all
humanity! I only know that I felt I could not bear my happiness aright
until I had, so to speak, consecrated it by some act of love.
I slipped my letter into the bosom of my dress, turned down the lane
which ran at right angles with that leading from the cottage, and
walked swiftly on. On I went, without thinking whither; yielding to the
impulse upon me, without pausing to ask myself how far I should have to
go, or what I should find to do in those silent lanes. Was some subtle
influence at work with me, of which at the time I was not conscious?
Was some guardian spirit leading me towards an end it was not necessary
for me to see? I only know that I shall never believe it was only
chance which led me to a certain spot that night!
SUBMARINE CABLES.
THEIR MANUFACTURE.
Twenty-seven years ago the first submarine cable was laid across the
Strait of Dover. This was a single copper wire covered in gutta-percha,
which parted next day; and the first practicable submarine cable was
laid in 1851, on the same route. Since then the progress of ocean
telegraphy has been extraordinary; no fewer than six cables spanning
the Atlantic bed--five to North America (although these are not all
working), and one to South America by way of Madeira and Pernambuco.
And so extensive is the already existing network of foreign cables,
that when Asia is united to America by cabling the Pacific, the
electric girdle round the world will be complete from east to west, as
it now is between north and south.
In this great development of telegraphy our countrymen have
unquestionably furnished both the lion's share of the work and the
capital. The cables have nearly all been manufactured in London, which
is the headquarters of telegraphy.
The principal parts of a submarine cable are: the _conductor_; the
_insulator_; and the _protector_ or sheathing. The conductor, as its
name implies, is the wire which conducts or conveys the electric
current from one place to another. It corresponds to the iron wire of
our ordinary open air or land lines of telegraph. Along this wire,
as is well known, the current from the battery at the station from
which the message is being sent travels to the station receiving the
message, where it passes to the earth, and appears to return through
the earth to the battery again; thus _completing its circuit_.
There are two distinct parts of the circuit which the current has
to traverse--namely, the outgoing part, represented by the wire or
_conductor_; and the return part, represented by the earth itself; and
inasmuch as these two parts must be kept distinct and apart throughout
their length, the wire which is laid along the earth's surface must
be kept apart from the earth, to secure which the conductor is
entirely surrounded with an _insulator_. In land lines, erected on
posts overhead, the wire is separated or insulated from the earth by
the air, which is, when dry, the most perfect insulator known; and
at the points of support, contact with the earth is prevented by the
use of porcelain, stoneware, or vulcanite 'insulators,' to which the
conducting wire is fastened.
An insulator is a non-conducting substance, impervious, so to speak,
to electricity. It is the theoretical antipodes of a conductor. While
the conductor is a substance through or over which electricity flows
freely, the insulator will neither permit electricity to pass through
its mass nor over its surface. It can therefore be used as a means of
confining electricity to a conductor, and preventing it from escaping
to other conductors in the neighbourhood. In short it can be made to
insulate or isolate the particular conductor from all other conductors.
Its use in a submarine cable is to confine the electric current to the
conductor or wire, so that it travels along it from one station to the
other without escaping to the water, and through that to the earth
(which, as we have already said, is the neighbouring conductor, and
the return part of the circuit) on its way. It is therefore of course
important that there shall be no flaw in the insulator, and in order to
protect it from strain and violence, it is covered with a strong guard
or sheathing. This outer sheathing or protector, which is composed of
twisted metal strands, is purely mechanical. Only the conductor and the
insulator are concerned in the _electrical_ requirements of the cable.
The conductor is invariably of copper wire, that metal being chosen
because, next to silver, which is of course too expensive, it is the
best metallic conductor of electricity. The metals, as distinguished
from most other minerals, are excellent conductors of electricity; that
is to say, they oppose relatively _less resistance_ to the passage of
the electric current through their mass. There is an economy of power
in using a good conductor for the telegraphic line. The current is less
weakened when the resistance to its passage along the line of wire is
less, and it is therefore capable of more powerful effects throughout
the route, and consequently at the other end. The conductivity or
conducting power of a wire increases with the thickness of the wire;
and therefore by taking a thicker wire of a more common metal than
copper (such as iron), the resistance to the passage of the current
may be made as small as when a thin copper wire is employed. But it is
important that the conductor of a submarine cable, especially of a long
one, should be of as fine dimensions as possible, in order to economise
insulating material and sheathing, and reduce the total weight of the
finished line. Therefore the advantages in point of price of iron wire
over copper in the first place, would be greatly overbalanced by the
increased cost of insulating and sheathing it. It is of the greatest
importance that the copper wire of the cable should be as pure as
possible, for the slightest trace of arsenic or other foreign element
is sufficient to hamper, in some mysterious way, the swift course of
the subtle current, and very materially to weaken the conducting power
of the wire.
In a few cables the copper conductor has been made in the form of a
single thick wire; but for the sake of greater flexibility and less
risk of breakage, it is generally made in the form of a strand of three
or more, and frequently of seven wires; six set round a central one.
The wires are wound together in a spiral strand, and their interstices
filled with an adhesive substance called Chatterton's Compound, a
mixture of resin, gutta-percha, and Stockholm tar. This compound not
only renders the strand solid, and impervious to water, but also acts
as an adhesive connection between the copper conductor itself and the
insulator with which it is to be coated. Bound together with this or
similar pitchy compounds, the conductor and the insulator form a solid
_core_ expanding and contracting together.
The insulator is always either of gutta-percha or india-rubber, but
most frequently the former; and it is of course essential that there
shall be no flaw or defect, such as an air-bubble or steam-vesicle, or
hair or thread inclosed so as to deteriorate its insulating properties.
To guard against such accidents, it is usual to apply a series of
coatings to make up the total thickness of the insulator. Accordingly,
when one coating has cooled, a layer of Chatterton's Compound is
applied to it, and another coating overlaid, and so on, until the
required amount of insulating material has been put on.
Whether the insulating substance is gutta-percha or india-rubber, there
is generally wound round it a serving of untarred hemp or jute yarn,
which has either been tanned or soaked in brine as a preservative. This
is to act as a padding or cushion for the iron sheathing or protector
next to be applied. This serving is applied in the following way. A
circular disc or frame, carrying on one face a series of bobbins which
hold the threads of the yarn, is kept revolving. The core is made to
pass through a hole in the centre of this disc, and the threads are
wound spirally round it as the disc revolves.
The iron wires of the sheathing, which completely inclose and cover
the served core, are wound on by the powerful 'cable machines,' whose
operation is so interesting a feature in a visit to a cable factory.
The great revolving disc, seven or eight feet in diameter, is set round
with iron bobbins filled with the iron sheathing wires. These bobbins
are _suspended_ on the face of the disc, so that as the disc revolves
they always preserve their fixed position with respect to the earth.
In this way the wires themselves are not twisted round their own axes
as they are laid on the core. These wires are generally of the best
homogeneous iron wire, that is, a wire intermediate in quality between
iron and steel, and uniting some of the toughness of the former to
the strength of the latter. They are sometimes themselves covered
with a serving of the best tarred Manilla hemp; sometimes laid on
in single wires abutting against each other, so as to form a smooth
and complete casing for the cable; and sometimes they are applied in
strands of three wires, each abutting against each other. The composite
sheathing of hemp and iron is usually applied to the deep-sea portion
of a cable where, in laying, a union of lightness and strength is
demanded, and where, when once laid, the cable is not likely to be
molested. The single-wire sheathing is applied to cables to be laid in
shallower depths, such as coast-waters; and the heavy-strand sheathing
is for protecting the cable in anchorages and on sea-beaches. The
light-sheathed cable is called 'main' or 'deep-sea cable;' the medium
is called 'intermediate;' and the heavy-sheathed cable is called
'shore-end.' There is seldom more of the last than ten or twelve miles,
to carry the cable well out of reach of the abrasion of storm-shifted
boulders and coast anchorage. The intermediate usually extends until
deep water has been reached, where the deep-sea portion takes its
place. These three types of cable are connected together by 'taper
pieces.' The core is of course uniform throughout the entire length of
the cable; but the taper pieces serve to connect the different types
of sheathing artistically and soundly with each other. The intermediate
cable generally has its sheathing wires covered with a serving of
mineral pitch, silica, and hemp of a coarse quality, in order to ward
off as long as possible the dissolving action of the sea-water.
The cable being thus finished at the manufactory, it is coiled into
large iron tanks, and there immersed in brine until it is shipped for
transport and laying.
All the materials of a submarine cable are carefully watched and
tested--the iron wire, for stretching, twisting, and breaking stress,
and the core for all its electric properties. The special properties
of every knot or mile of the core are chronicled, so that a complete
account of every part of the cable is preserved during its progress
of manufacture. And after it is made, it is tested electrically every
day, to see that no change takes place in its electric qualities. These
electric tests are three in number: For _resistance_--the resistance
of the copper wire to the passage of the current. For _inductive
capacity_--the amount of charge or quantity of electricity which the
cable will take up. For _insulation resistance_--the insulating power
of the gutta-percha coating.
These tests are made by direct comparison with units, just as bodies
are weighed by comparison with a pound or unit of weight. The unit of
electric resistance is the _ohm_; so called after the celebrated German
physicist and electrician Ohm. The ohm is the resistance of a certain
length of platinum-silver wire determined by a Committee of the British
Association. Multiples of the ohm are readily obtained, and these are
arranged and made up into what are called _resistance-boxes_--the
practical tool of the electrician. A resistance-box usually contains
coils of platinum-silver wire of from five thousand ohms downwards to
single ohms or fractions of an ohm. It is with this finely graduated
tool that the electrician compares the resistance, or in other words
ascertains the conducting power of the cable.
The unit of measurement of the _insulation resistance_ of the
cable is a very high multiple of the ohm, called the _meg-ohm_ or
million-ohms; for inasmuch as the insulator is, technically speaking,
a non-conductor, its office is to exercise the necessary resistance
to the escape of the current. The unit for capacity is called a
_micro-farad_ or millionth part of the _Farad_, which derives its name
from Faraday, and represents a certain _quantity_ of electricity.
The practical tool for the micro-farad is a contrivance called a
_condenser_, a description of which, without the aid of drawings, would
be too technical for our readers. A submarine cable is itself, however,
a particular form of such a condenser. The copper wire is one of the
opposed conductors, the sheathing, earth, and sea-water form the other,
and these are separated from each other by the insulating coating of
gutta-percha. It is a curious fact that when a charge of electricity
is communicated to the copper wire of a cable, it _induces_ a charge
of an opposite kind in the earth outside. This inductive property of
an insulated wire contiguous to the earth has an important bearing on
practical telegraphy; for inasmuch as the communicated charge and the
induced charge attract each other, the former travels less swiftly
along the wire; it is held back, as it were, by the retarding influence
of the earth's induced charge; or in other words has a tendency to
ooze out of the cable instead of travelling uninterruptedly to the
other end. It is of consequence, therefore, to ascertain the inductive
capacity of a cable; as the less it is, the greater will the _speed_ of
signalling be.
The resistances and capacity of a cable are usually tested, according
to the standards of resistance and capacity--that is, with the ohm,
meg-ohm, and micro-farad--by measuring the strength of an electric
current passing through the cable, by means of an instrument called
the galvanometer, or current measurer. Its principle depends upon the
fact, discovered by Oersted, the famous Copenhagen philosopher, that
when a current is sent along a wire in the neighbourhood of a freely
suspended magnetic needle, the needle will be deflected into a new
position, and this position will be to right or to left according
as the current of one kind or the other is sent through the wire.
Moreover, the amount of deflection will be directly proportional to
the _strength_ of the current. This great discovery, which gave an
incalculably great impetus to the progress of the telegraph, is the
theoretical basis of the galvanometer. One form of this instrument,
used to test submarine cables, is called the 'reflecting galvanometer,'
and is the invention of Sir William Thomson. The wire through which the
current to be measured is made to pass, consists of a great many turns
of silk-covered or insulated copper of a very fine gauge, forming a
hollow coil, in the heart of which a very diminutive magnetic needle
is suspended by a gossamer-like filament of floss silk. This magnet
(or magnets, for there are generally more than one) carries a tiny
circular mirror, the whole arrangement of magnets and mirror being no
longer than (=) [Transcriber's note: The parallel lines in the original
shown here by = were 2mm (1/16") apart and 3mm (1/8") long.]. A beam of
light is thrown from a lamp in front on to the mirror, and reflected
back again on to a graduated pasteboard scale. When the current to be
measured is sent throughout the coiled wire surrounding the magnets,
they are turned horizontally on their former position, and the mirror
is inclined round with them, so that the reflected beam of light is
moved along the scale, the distance to which it is moved being a
measure of the current strength.
Now when the current from a given battery or source of electricity is
made to pass through wires of different resistances, the strength of
the current which will pass through these wires can be made a measure
of their resistances; and therefore, when the current from a particular
battery is sent through the conductor of the cable or to test the
insulator, and in each case measured by the galvanometer, and compared
with the current from the same source which will flow through the units
of comparison, the copper resistance and insulation resistance can be
obtained.
In a somewhat similar way the capacity--the _amount_ of electricity
which a cable will take--is compared with the capacity of a standard
condenser or measure of capacity. The opposite plates or sheets of the
condenser are charged by a particular battery; and as these charges
are eager to flow into each other and unite, but are held apart by
the insulator, they may be allowed to do so through a wire or other
conductor. The discharge of the opposite electricities into one
another sets up a short powerful current in this wire, and its strength
is proportional to the quantity of electricity discharged; that is,
to the capacity of the condenser. If the coil of the galvanometer be
substituted for this discharging wire, the strength of this discharge
will be measured by the deflection of the gleam of light on the scale.
By charging alternately, therefore, the condenser and the cable from
the same battery, and observing their respective discharges by means
of the galvanometer, the capacities of the cable and condenser are
compared.
The speed of signalling through a submarine cable, that is to say the
number of words per minute that can be transmitted through it, varies
with the resistance of its conductor, its inductive capacity, and its
length; and it is by a consideration of these properties, together with
weight and cost of material, that its form and dimensions are designed;
and on this interesting subject we may have a few words to say in a
future paper.
LIFE IN ST KILDA.
FIRST PAPER.
For the following interesting account of the island of St Kilda, we are
indebted to Mr J. Sands, a gentleman who has more than once visited
the rock, and who upon one occasion was detained there for several
months by stress of weather. As will be seen by his narrative--the
first portion of which we now offer to our readers--he utilised his
opportunities for observing not only the manners and customs of the
natives, but many curious facts connected with the natural history and
even the archæology of the islet. With these few words of preface, we
leave Mr Sands to tell his story.
Far out in the Atlantic--forty-nine miles west from Obe in the Sound of
Harris, and forty-three from Shillay in the Outer Hebrides--there is a
group of islands, evidently of volcanic origin, the largest of which,
called _Hirta_ by the inhabitants, and St Kilda by strangers, contains
a small community who speak Gaelic only, and have all Highland names.
This island, which is about three miles long by two broad, is bounded
on the north-east and south-west by enormous precipices that rise like
walls out of the sea. These cliffs are frequented by vast numbers of
sea-fowl; by puffins, cormorants, guillemots, auks, and other birds. A
species of gull called the fulmar also abounds, and is of great value
to the inhabitants, who salt the flesh for food in winter and sell the
oil and feathers. St Kilda is the only island in Great Britain where
that bird breeds. About three miles to the north-east of St Kilda is an
island called Boreray, which is the great resort of solan-geese, which
also frequent the _stacks_ or isolated rocks adjacent.