The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1892-06-26

49, oshei. Inc nrst long distance lines
80 single circuits with no other wires
near ,neih, but when the work was taken
up with view to providing regular .eIe-
Pnohe service between different cities lines
80 ouht containing dozen or more me-
TIT circuits carried on the same poles.
nheh a somewhat unlooked-fo phenome-
| I'm was encountered. Ii was found that
mere was strong induction from one cir
ouit 10 anothcr-that the conversation
soilg on over one circuit could be heard
on any OF the others. This was a serious
o'pacA, as, OF course, 1t was impossible
| " open line for public service
unuer such conditions. Months
Gnau. spent IN experimenting. and
Hhaiiy remedy was discovered. By
arranging the wires in a certain manner
Oh the poles the overhearing was done
away with. The object sought for and
OBTAINED was 10 so place the wires in rela-
tioh 10 each other that the currents in
uucea In one side of a circuit should neu-
traiize the currents induced i'm the other.
mus 1nus leaving the telephone unaffected.
me Key to the problem having been
.ouho IL Is comparatively simple matter
10 design disposition of wires for line
Ei any number Of circuits that will abso-
!uteiy prevent any induction or overhear-
ing from one circuit to another.
Inc instruments used in long distance
telephone work do not differ greatly from
.nose used In the local exchange systems.
Inc receiver IS precisely the same instru-
lleht, put more powerful form of trans
nhitter has been adopted in order to allow
d margin for loss In transmission over the
iong Hnes. The gain IN carrying power
secured IN this way, however, is not very
great. land the real problem of long distance
telephony Is in the line rather than in the
Instrument. As we have already seen the
nrst desideratum is to provide quiet line.
lree from all disturbing influences OF earth
currents and induction-the voice current
must have a fee path and be left in sole
possession OF 1t. Then comes the question
Oh the distance to which the voice current
can DE carried with sufficient of its original
lorce TO produce clearly audible effect in
the distant receiver. This question is
mainly dependent on the conditions of the
nne. 1t can be easily understood that an
instrument operated by such a compare
lively feeble source of energy as the human
voice must have narrow limits of power.
Telephone transmitters cannot be success
luily operated with more than a certain
amount OF battery power. the maximum
USED at present being only fraction of that
employed In the working of long telegraph
lines. In the transmitter the battery cur
rent is transformed by means of an induc-
tlon coil to an attenuated current of
higher tension which is sent out to
line with the waves and undula-
lions that ere impressed upon it by
the vibrations of the human voice. Now,
there are two conditions of the line
which limit the distance the telephone cur
rent can be effectively transmitted These
are what electricians call resistance and
capacity. Resistance is a sort of friction
that opposes the passage of the current;
every mile OF wire has a definite resist
ance, thin wires having higher resistance
than thicker ones, so that the longer the
line the greater the resistance. The effect
OF resistance IS to diminish the volume of
the telephone current, and therefore the
loudness of the speech received at the
distant end. Capacity is peculiar prop
erty that an electrical conductor has O:
accommodating charge OF electricity on its
surface before allowing any current
to pass out at the far end OF the
conductor: This phenomenon is due
to the effect OF the magnetism of the
earth on conductors placed within its in
tluence, and it varies according to the dis
tance above the earth at which the con-
ductor Is suspended and according to the
material with which the conductor is in
sulated. An overhead wire, which is in
sulated from the earth by the intervening
air, suspended at a height of twenty or
thirty feet above the ground, has a very
low capacity; an underground cable, which
is only separated from the earth by
slight thickness of insulating material, has
about ten or twelve times higher capacity
than the overhead wire. and a submarine
cable, which ls everywhere in close con-
tact with the earth, has the highest
capacity of all about thirty tunes
that of the overhead wires The effect of
capacity on the telephone current is to
deaden and mutfie the dlstinctness of the
speech by absorbing, as it were, part of the
rapid undulations and checking the speed
of their travel along the wire. AS the clear
reproduction of speech IS dependent on the
perfect transmission of thousands of these
tiny undulations per second, the liability
of the telephone current to sufier from the
effects of capacity can be appreciated
Capacity is the greatest bugbear of the teie-
phone engineer; ii limits the distance at
which he can talk overland, it cuts down
his margin to an abnormal extent when he
is forced to work through underground con-
ductors and prevents him from attempting
telephone line OF any length under the
| sea. Here, as before, we see that the earth
| can be anything but q benefactor to the
electrician. Ii telephone engineers could
| suspend their wires from line of balloons
| anchored at q height of several miles above
the earth the influence of capacity would
| be practically nil, and it would be easy to
| talk from New York to San Francisco. If
they could construct q cable provided with
| a screen that would shield the conductor
| from the retarding effect of the earth's
magnetism the problem of ocean telephony
| would be solved, and London and New
| with each other Perhaps before very
| long this will be accomplished.
The first really long distance telephone
| line in the United States was built in 1883
| to connec. New York and Boston. The
| work was carried out by the American
| Bell Telephone Company 10 test the USE
| fitness of long distance telephony from q
| commercial point of view and its practical
! bility from the scientific side of the ques-
| ton. At that time a telephone circuit go
| miles long which should give good and
| trustworthy service was quite sclentlnc
| feat. Successful working was attained by
having great attention to the careful con-
struction of the line. As We have already
| seen in the problem OF telephone commu-
| nication over long distances the line is
| the principal factor, owing to the extreme
| delicacy of the instruments and their very
| limited range of power; the line must
! be so constructed as TO prevent the
| introduction of outside disturbances
| and to cause the minimum OF loss
| in transmission of the telephone current
| The New York-Boston line was metallic
| circuit. built Of hard drawn copper wire,
| carried on high poles as far removed as
| possible from the neighborhood OF other
| electric wires. and from danger OF contact
| with trees which would affect the lnsula-
ton of the wires IN wet weather ana cause
| the appearance of earth currents IN the
| circuit. This line was found To work ad-
| mirably. and no trouble was experienced
with electrical disturbances OF any sort;
| conversation could be carried on between
| New York and Boston with as much ease
| rs over local telephone circuit only q mile
or so long. NJ
A wear or two later the American Tele-
| phone and Telegraph Company, colioqul-