The Democratic advocate. [volume] (Westminster, Md.) 1865-1972, 1869-07-15
How the Atlantic Gable is Worked.

" eNS "VAtuS VI tue Atiautfc
Cable 10 recent lecture by the Hon.
VIM. j. McAlpine. on the subject Of
=" Modern Eugineering:"
Telegraphy may, with propriety, be
considered one Of the branches Of en-.
gineering, and is peculiarly of modern
development. A clever writer says
that it may be read by each of the Eve
senses. On land lines each signal is
made BY suspending the flow Of the
electric current for two different iuter-
vals Of time called "dots and dashes"
the use Of which, in different orders,
constitutes the alphabet Of the telegraph.
When these are printed they are read
BY "sight," but ordinarily the operator
reads them by "sound" as easily as a
musician reads the letters of the scale
BY the same sense. If the operator has
no instrument, he will grasp the wire
in his hand aud read the signals by
" feeling" the intermissions Of the flow
of the electric current. In like manner,
BY placing the wire across the tongue
he can "taste" the same intermissiou.
but this is dangerous experiment.
And it is said that the electricity can
be made to dissolve chemical and pro.
duce pungent odor in the teIegraphic
alphabet, which can be read by "smel.
ling" but for this l do not vouch. /
believe that the method Of signalizing
through the Atlantic Cable is known
in detail to but few persons. The oper.
alton is exactly reversed from that Of
the land wires.
The gutta- -percha covering of the cop
per wires, under the pressure of great
depth Of water, becomes an absorbent
Of the electricity which is being sent
through them to the extent Of 90 per
cent. The first portion of the electric
wave OF 10 per cent. crosses the ocean
(l,700 miles) in two seconds, aud il
would be followed by succession of
waves from the restoration of that por-
tion OF the electricity which has been
absorbed by the gutta. percha 10 i'm.
pulses, and the signal would be repeated
like echoes, and produce not only confu.
sion, but great delay. To remedy this
Professor Varly introduced a key, which
sends alternate currents; positive aud
negative, at such intervals ss allow the
first wave Of 10 per cent. to pass for.
ward, aud then that portion absorbed
by the covering Is neutralized by its
opposite, and the cable is cleared for
the transmission OF a second pair Of
currents. The battery used is a very
small one, (tbree of Daniels cups, } and
the signal being 10 per cent Of this
small current, is powerless to move any
OF the other instruments in use on land.
The instrument used consists Of q mi.
mute polarized needle. suspended on a
single strand Of a spiders web, or one
from the silk-worm. In the middle Of
this minute needle is placed au almost
microscopic mirror, which reflects sin.
gle ray Of light from a powerful lamp.
The currents Of electricity afIe,t this
needle alternately to the right and left
for space Of time corresponding to
that occupied iu the signal Of the land
line, the same kind OF alphabet being
used In ooth cases. The receiver (not
operator sits 10 DARK room, and the
small mirror reflects the ray Of light
upon piece OF white paper before him,
on winch . black line Is drawn, to the
rignt and ieit OF which the light is al
ternateiy renected. The receiver reads
these signals by "slght," and transmits
them 70 another person, placed outside
Of the DARK room, by means Of on o-di-
nary instrument.
a short time since, General Reynolds
toia me tnat he had sent message,
Wi,hoat either wire or cable, ninety-two
miles across an arm Of Lake Superior,
oy means oil the heiiotrope or mirror,
ana On the return OF his messenger,
VINO nad been sent with written copy,
ae iound 'nat the heliotrope message
mao been receiyed, understood and
ooeyed.
ne mad two assistants. who had been
telegraphic operators, who had for a
Wnoie summer Deen amusing themselves
~ .aiking 70 eacn otner with these
iubtfumeBts, th0ugn tney were stationed