Year: 1865




The London Telegraph of May %, has the
following inte resting account OF the pre-
parations on board the Great Eastern for
laying the ocean telegraph cable


DIFFERENCE BETWEEN 1858 AND 1865


A visit was paid to the Great Eastern a
few days since by large party of the di-
rectors' friends and it may be said that
all who understood the preparations which
they saw came away with a greatly
strengthened confidence in the future of the
new cable. Since 1858, when the first At,
antic line was laid the advance that has
been made by the scientific world towards
comprehending electrical phenomena is
very great. 1t has been said, by a man
well qualified to speak on the subject, that
electric science has passed. since that time,
| from its childhood to its maturity. So far
as the phenomena connected with long cleo
trio circuits were concerned, we had in 1858
no knowledge whatever. The instruments
in common use were unsuited to receiving
signals through a great length of cable
the necessity of providing for the conduc-
tor an insulation so perfect as to approach
an absolute condition was inadequately APP
preciated The best preliminary test for a
long cable had not been devised, and the
old Atlantic telegraph was laid without
having been subjected to any searching
test on shore Everybody had advice to
give concerning the management of the
wire, but no one recommended the precau-
ii )ns which subsequent experience has
shown to be necessary. When the signals
began to fall the battery power was aug
mented, and electromagnetic induction
coils, which rapidly helped on the destruc-
ton of the conductor were put in circuit
No one thought of " nursing" the cable
of humoring it's feeble attempts at articu-
late utterance and of finding what it said
rather by listening acutely than by con-
stantly calling on it, in the language ofthe
Victoria gallery, to "Speak up" The old
cable, however, is dead and gone part of
it has been picked up and applied to igno
bic uses, as a racehorse past his work may
be put into the sh ats of a hanson part
of it has been abandoned, and lies where it
may rest till the end of time, in the clark
unfathomed caves of the deep sea. Let
us turn to the practical present.


SCENES ON BOARD THE GREAT EAsTEEN


The Great Eastern looks just now more
like an engineers workshop than a sea-
going ship. The vast expanses Of her deck
are covered with wooden sheds and piles of
timber. There are smiths forges below,
and between the decks you might fancy
yourself in machinist's factory. The
great engines of the ship, it is true, have
lost the bright look of machinery which is
in constant use and the huge dull masses
of iron seem asleep, or in a trance. If you
descend the ladders which lead to the boil
ers and furnaces an expedition which is
more like going down a mine than any
other to which it can be compared-you
find yourself in the midst of darkness, soli-
tude and cold but in those regions of the
vessel where the cable is being shipped
and watched there is every sign of keen,
vigilant intelligence. When you under
stand what is being done, you see some
thing more than this--that scientific fore
step and that the thick tarry rope, coarse
and rough to appearance, which lies coiled
away under water in the tanks of the ship,
is manufactured, scanned, and tested with
as much care as the incest optical instru-
ment in an astronomers observatory, or
most delicate apparatus of fragile glass
ever applied to the careful experiments of
chemistry.


THE SCIENTIFIC TESTS.


1t seems impossible that there can be
any fault in the Atlantic cable when the
Great Eastern goes to sea. To say nothing
ofthe tests applied to it at the manufactory,
it is tested not alone after it has been taken
on board, but during its delivery into the
ship AS soon as length is brought along
side, one end is connected with the coils al
ready on board, and the other end with the
instruments in the testing room. The Cir
cult is thus made through the whole extent
of the coil, the portion on board and the
portion alongside The process of hauling
in then commences, and the insulation is
continuously observed. The instruments
in the testing room record the smallest de-
Walton from absolutely perfect insulation.
1t will be understood that an insulation
which shall be quite perfect, as an cleo
trician understands the word, is not at
tainable. A piece of metal separated by
means of the purest glass, and enclosed in
the driest atmosphere that can be obtained,
will, if charged with electricity, lose that
electricity after a time. In speaking of
insulation we must therefore be understood
to mean an approximate condition but
the approximation in the case of the new
Atlantic cable comes so near to perfection
that this rough tarry rope is a scientific
wonder.


The last dying pulsation of the old At
lantc cable was forced through it by means
of galvanic battery consisting of two
hundred and forty cells. The submarine
telegraph from London to Amst erdam is
habitually worked with battery of fifty
cells, and such battery is commonly used
for the other submarine lines of Europe
Signals have been repeatedly sent through
more than thirteen hundred miles of the
cable now on board the Great Eastern by
means of one CELL Galvanic currents so
feeble that they could not have been felt
by the hand, and might have been passed
harmlessly through circuit completed by
the operators tongue, can be used to con-
vey messages along length of cable that
would very nearly stretch from London to
St Petersburg. Over needle instruments,
such as those in ordinary use for land tele-
graph, current from one cell would be
powerless.


To record such faint pulsations of elec-
tricity, it is necessary to use Professors
Thompson's mirror galvanometer. This
beautiful instrument consists of a mirror
oh bo ,;,o &C n four nanny pinoa rna6a