Year: 1865

The London Telegraph of May 2S has the fol-
lowing interesting account of the preparations
on board the Great Eastern for laying the ocean
telegraph cable:


DIFFERENCES BETWEEN 1858 AND 1866.
A visit was paid to the Great Eastern few
days since by large party of the directors
friends, and it may be said that all who under
stood the preparations which they saw came
away with greatly strengthened confidence
in the future of the new cable. Since 1858,
when the first Atlantic line was laid, the ad.
vance that has been made by the scientific
world towards cOmprehending electrical phe-
nOmena is very great. 1t has been said by
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 electric
circuits were concerned, we had in 1853 no
knowledge whatever. The instruments in
common use were unsuited to receiving signals
through great length of cable; the necessity
of providing for the conductor an insulation so
perfect as to approach an absolute condition
was inadequately appreciated.


The best preliminary test for long cable
had not been devised, and the old Atlantic tele-
graph 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 pre-
cautions which subsequent experience has
shown to be necessary. When the signals be-
gan to fail the battery power was augmented,
and electromagnetic induction coils, which
rapidly helped on the destruction of the con-
ductor, were put in circuit. No one thought
of "nursing" the eable-of humoring its feeble
attempts at articulate utterance, and Of finding
out what it said rather by listening acutely than
by constantly calling on it, in the language of
the Victoria gallery, to "Speak up" The old
cable however, is dead and gone; part of it
has been picked up and applied to ignOble uses,
as race-horse past his work may be put into
the shafts of Hanson; part of it has been
abandoned, and lies where it may rest till the
end of time, in the "dark unfathomed caves"
of the deep sea. Let Us turn to the practical
present.


SCENES ON BOARD TIE GREAT EASTERN.


The Great Eastern looks just now more like
an engineers's workshop than q seagoing ship.
The vast expanse 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 fac
tory. The great engines ofthe 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 q trance. If you
descend the ladders which lead to the boilers
and furnaces-an expedition which is more
like going down mine than any other to which





the midst of darkness, solitude 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 understand what is being done, you see
something more than this-that scientific FORE
sight of the highest order directs every 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 instrument in an astronomers
observatory, or the most delicate apparatus
of fragile glass ever applied to careful expert
ments Of chemistry.


THE sCIsNIIFIc TESTS


1t eeems impossible that there be any fault in
the Atlantic cable when the Great Eastern goes to
sea To say notbiug of tie tests app led to 1t al the
manutaesory, it is tested not alo after it has been
taken board but during its delivery into the ship
AS as a length is BIO ght alongside, one end is
connected wi b the coils already on board and the
other end with the instruments In the testing room.
The circuit is thus made through The whole extent
of the COIL the portion Or, board and the portion
alongside. The process of hauling in theo COM
mences and theinsulatiol Is continuously observed
The Instruments In the testing room record the
smallest deviation ON a5sOl tey perfect insulation.
It will be understood that an nsulaiion which shall
be quite Perfect as an electrician understands the
word, is not tainsble. piece OF metal separated
by means of the purest glass and enclosed in the
driest atm sphere that can be obtained, WILL if
charged with ele trcity lose tnat elecuiciy after





be understood to mean an approximate condition
but the approximation in the case OF the new Atan
tic cable comes to perfection that this rough
t Try rope is a scientific wonder.


The last diving p lsa ion the cid Atlantic cable
was forced through it by means of galvanic bat
terry consisting of wo hundred and forty cells. The
submarine telegraph from London 10 Amsterdam is
habitua Ally wcrsed W tn ba tery Of fifty cells end
such battery is commonly used for the other sub
mar ne lines of Europe Signals have been repeat
edly sent through more tian thirteen hundred miles
&c ill., 1lo A. (y.oa Eock t,
means of one cell. Galvanic currents feeble nat
they could thave been fe by the hand, and might
have been pas ed harm'essly through circuit COM
peted ny the operators tongue can be used to con-
vey messages along length of cable that would
| We ne ,rly stretch from lOnden to St Pelet burg.
Over needle instruments such as tn Sc in ord nary
use TOR land telegraphy, current from oIe cell


To record such faint pulsaions of electricity it Is
necessary to use Profes Thompsou's mirror gal
vanometer This beautiful instrument GOES sts of
Mirror about he size of fOurpenDy piece. mads OF
micro cope g,a &, and 60 thin th3i l. weighs On
| grain. On the back of this mirror minrte n ag-
net Is fred, al d thu supp emented it is suspended
BY slsen fbr. in the heart col of wire so
that any cur ent passing trough the coil d fleets
tn ma net and the mirror along with it. ray of
Hg: ,cted by the irr falls on tcaie di: tant


Dtss 81 rsnt ana Of
these movements represent the difereGt letters OF
the alphabet, and thus the apparently erratc wan
dericgs Of ray Of light are made to convey inte l.





used to test the able as it is haule1 on board and
if any fanlt had existed it could not have passed
without election. Up to this time when there are
on board the ship and alongside 197O mile, Of cab
| no fault has been discovered.


THE IMMERSION.


The ma hinery for paying ont il not yet on board
| but Is being put toyeIh r at the Greenwich worss
The process of immersion viii take about q fort.
night The begi nIng of the shore end will be laid
by email vessel. which will meet the Crest Eas ern
about twenty miles from the Irish coast The cable
will then be passed on board, connected with that in
the great tanks and the big chip will begin her voy
age. To the nil lated this process OF cutting ard
joining the cable appears very mysterious, bnt the
engineers who used to the w0rk face it without
any hesitation. The joints do net really eneanger
either the insulation or the strength OF the cable
wherever they m de the external and conductn
wires are splced along considerable length-sdme.
es not less than thirty yards-ard the gutta per-
cha carefully put in separate layers firmly pressed
together by meas of warm irons. The complete
ness of the joint tested by LAYING 1t p insulated
metailic vesse, contsining water and ascsrtaining
by means of tests applied to this vessel whether any
electricity escapes frssm the join. as current is
passed along the cable