, 1900-10-12

The events of the past two years
have been given an increased interest
in the remote parts of the globe that
has never been so widespread among
our people as now. The Philippines,
the Transvaal and China have ceased
to be mere geographical facts, but
have become real places of which we
know something and from which we
demand news with as slight delay as
possible. The Geographic cables
therefore today hold an important
place in minds that previously had
given them but little consideration.
1t is strange how few people know
anything of the oceanic Geographic
service, says a writer in the Washing
ton Star. A vague idea that it is car
ried on by cables" is about all that
the ordinary person possesses, but
what a cable is. how it is operated or
what difficulties lie in the way Of its
construction, are all unknown to the
bulk of well-informed people. The ac-
counts of them are generally SC incum-
bered with t~echnicalties as to be al
most unintelligible to unprofessional
readers, and, in consequence, they are
wrapped in more mystery tina are
many things that enter into everyday
life. Most people think that there is
no more difference between submarine
and land %telegraphy than there is be-
tween an overhead and ar under
ground trolley line, but this is not
true. They are absolutely distinct,
and have little more in common than
have a great railway system n a
horse car line. If so much. Both tele-
graphic systems use electric currents
to transmit signals over a Conducting
wire, as both the railway and the
horse car line use vehicles that move
on n track. but all else is different.
In order to understand why a route
for a cable is always sought with much
are the structure of the cable itself
should be known, for on its safety de-
ponds the success of the enterprise. A
cable consists of a Gore" of wire that
is really the important part OF the
whole, and a covering of some insulat-
ing and protecting material. The core
is made of strands of copper woven in
to a rope-like cord, and weighs from
20 to 400 pounds per mile-for the
shore ends that have to stand the surf
are much stronger and heavier than
the deep sea portions. The stranded
form is much more flexible than the
solid rod. and is not so apt to be bro
ken in laying. The core is coated with
a mixture of resin, tar and gutta per-
cha, known as "Chatterlon's COM
pound" that Is to act as a cement and
hold the insulation firmly to the wires.
The insulating material must COM
ply with many requirements. 1t must
not conduct electricity and must pre-
vent leakage" as much as possible; 1t
sea water will DOR corrode the copper
IL it reaches it, and will steal the cur
zen If there be the smallest hole
through which 1t may reach the wires.
It must resist the chemical action OF
the water on itself. and 1t must be
flexible and tough, so that the cable
may be coiled into a small space on
board ship and run over pulleys when
being laid without cracking or tear
ing. Finally, 1t must be something
that does not decay readily and does
no dissolve in water. So far but one
material has been discovered that full
fills all the conditions. That is gutta
percha. a gum that is easily worked
and whose only drawback is its scar
city.
When the pure gum is heated to
about1 $50 degrees Fahrenheit it becomes
very soft and plastic. so that 1t car
be rolled or pressed into shapes that II
retains when cold. Advantage Is Ia
ken of this in making cables, for the
heated gum is forced through a cylin-
der surrounding the core and as the
core is drawn through a ~die-plece a
thin layer of gutta percha is left on 1t
This is repeated as often as Is required
and the core is thus covered with q
series Of gutta percha jackets that ex'