The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1906-07-22
Manner of Testing.


The wav in which tests of this sort
are made is curious. At one end OF the
laboratory is a telephone Instrument that
Is kent at an absolute standard dalI
way down the room is sound-prooi pootn
in which, a similarly perfect instrument
is installed. The telephone In the open
room has practically the surroundings OF
the ordinary subscribers premises; the
other is secluded so as to give as nearly
absolute quiet as possible and allow the
trained ear to Judge correctly the SOUNDS
that come over the wires. On sheit De
side each telephone stands device which,
by shifting Its keys and changing It's
electrical resistance, can be mace TO rep
resent the loop, as 1t is called, petWeei
the subscribers station" and the central
office Fastened to the wall are repeat
ing coils relays and condensers exactly
like those attached to every subscrio-
er's line I'm a regular exchange.
The devices that represent the outside
lines of the telephone system, whether
cable under city streets or open wire
on pole lines, are the most interesting
Of all They look like boxes two or three
feet long and six inches Wide. with
double line OF electrical switches ON the
ton Inside each box Is series, of cohtrlV-
ances each with the electrical resistance
and capacity of so much cable or wire,
as the case may be; and by manipulating
the switches any desired number OF the
sections of artificial line" as they are
called can be put into the circuit under
test The artificial lines are made by tax
ing the resistance Of the size OF wire
they are 10 represent, allowing Tor the IN
eyitable leakage of current under some
conditions and for the influence of induc-
ton under others. and then embodying the
result in single compact device which
will produce on any current that Is passed
through 1t the combined effects or all
these various influences
To Compare Efficiency.
When the engineers wish to compare the
efficiency of two pieces of apparatus.
each is connected with the same wires
through mercury switch" The switch
can be worked so as to put first one
of the samples under examination and
then the other into the test circuit one
observer talks into the instrument at the
open end of the line rocking the switch
back and forth while the other listens In
the sound-proof booth, noting the diner
ences in transmission caused by each
change of observation-disclosures which
to the unframed ear would be hardly
nerceptible Sometimes an actual operat-
inc nlant is compared with standard
eouipment like that used in the labora-
tory by means of one of these engineers
"layouts" and so sltilful does the ex-
merit become that he can determine with
practically absolute accuracy the pereen-
tage of efficiency OF the line or piece of
apparatus he is examining.
This laboratory and another one near
by. which is devoted to mechanical tests,
are important adjuncts of the engineer
ing department of the Bell telephone
system. The profession of the telephone
engineer has existed but thirty years and
has seen more progressive changes than
have taken place in any other profession
in the same length of time, The num-
Der of men whom experience has qualified
as experts in the highest sense Is prob
ably smaller today in this than in any
other profession. SO at Its headquarters
here the. Bell system maintains for the
benefit of all It's thirty-eight organiza-
tons, big and little, an engineering force
of $50 men to whom are referred the puz-
cling difficulties which require for their
solution a greater expenditure of time
and money, and wider resources than any
lesser organization could afford. These
are the men who have made the telephone
the wonderfully efficient thing 1t is today