THE TELAUTOGRAPH.
So far we have described several methods of electrical communication at
a distance, including the reading of letters and symbols at sight (as by
the dial-telegraph and the Morse code embossed on a strip of paper);
printed messages and messages received by means of arbitrary sounds, and
culminating in the most wonderful of all, the electrical transmission of
articulate speech.
None of these systems, however, are able to transmit a message that
completely identifies the sender without confirmation in the form of an
autograph letter by mail.
In 1893 there was exhibited in the electrical building at the World's
Fair an instrument invented by the writer called the Telautograph. As
the word implies, it is a system by which a man's own handwriting may be
transmitted to a distance through a wire and reproduced in facsimile at
the receiving-end. This instrument has been so often described in the
public prints that we will not attempt to do it here, for the reason
that it would be impossible without elaborate drawings and
specifications. It is unnecessary to state that it differs in a
fundamental way from other facsimile systems of telegraphy. Suffice it
to say that as one writes his message in one city another pen in another
city follows the transmitting-pen with perfect synchronism; it is as
though a man were writing with a pen with two points widely separated,
both moving at the same time and both making exactly the same motions.
By this system a man may transact business with the same accuracy as by
the United States mail, and with the same celerity as by the electric
telegraph.
A broker may buy or sell with his own signature attached to the order,
and do it as quickly as he could by any other method of telegraphing,
and with absolute accuracy, secrecy and perfect identification.
In 1893, when this apparatus was first publicly exhibited, it operated
by means of four wires between stations, and while the work it did was
faultless, the use of four wires made it too expensive and too
cumbersome for commercial purposes; so during all the years since then
the endeavor has been to reduce the number of wires to two, when it
would stand on an equality with the telephone in this respect. It is
only lately that this improvement has been satisfactorily accomplished,
and, for reasons above stated, no serious attempt has been made to
introduce it as yet; but it has been used for a long enough time to
demonstrate its practicability and commercial value. Companies have been
organized both in Europe and America for the purpose of putting the
telautograph into commercial use.
By means of a switch located in each subscriber's office the wires may
be switched from a telephone to a telautograph, or vice versa, in a
moment of time. By this arrangement a man may do all the preliminary
work of a business transaction through the telephone, and when he is
ready to put it into black and white switch in the telautograph and
write it down. For ordinary exchange work this is undoubtedly the true
way to use the telautograph, because one system of wires and one
central-station system will answer for both modes of communication, and
in this way an enormous saving can be made to the public. There is no
question in the mind of any one who is familiar with the operation of
both the telephone and telautograph but that some day they will both be
used, either in the same or separate systems, as they each have
distinctly separate fields of usefulness,--the telephone for desultory
conversation, the telautograph for accurate business transactions. The
question may arise in the minds of experts how the two systems can be
worked in the same set of cables, and this leads us to discuss the
phenomena of induction.
Every one who has listened at a telephone has heard a jumble of noises
more or less pronounced, which is the effect of the working of other
wires in proximity to those of the telephone. If, when a Morse telegraph
instrument is in operation on one of a number of wires strung on the
same poles, we should insert a telephone in any one of the wires that
were strung on the same poles or on another set of poles even across the
street, we could hear the working of this Morse wire in the telephone,
more or less pronounced, according to the distance the wire is from the
Morse circuit. This phenomenon is the result of induction, caused by
magnetic ether-waves that are set up whenever a circuit is broken and
closed, as explained in Chapter VI.
The telephone is perhaps the most sensitive of all instruments, and will
detect electrical disturbances that are too feeble to be felt on almost
any other instrument, hence the telephone is preyed upon by every other
system of electrical transmission, and for this reason has to adopt
means of self-protection. It has been found that the surest way to
prevent interference in the telephone from neighboring wires is to use
what is called a metallic circuit--that is to say, instead of running a
single wire from point to point and grounding at each end, as in
ordinary telegraph systems, the telephone circuit is completed by using
a second wire instead of the earth.
As a complete defense against the effects of induced currents the wires
should be exactly alike as to cross-section (or size) and resistance.
They should be insulated and laid together with a slight twist. This
latter is to cause the two wires so twisted to average always the same
distance from any contiguous wire.
One factor in determining the intensity of an induced current is the
distance the wire in which it flows is from the source of induction. A
telephone put in circuit at the end of the two wires that are thus laid
together will be practically free from the effects of induced currents
that are set up by the working of contiguous wires--for this reason:
Whenever a current is induced in one of the slack-twisted wires it is
induced in both alike; the two impulses being of the same polarity meet
in the telephone, where they kill each other. In order to have a perfect
result we must have perfect conditions, which are never attained
absolutely, but nearly enough for all practical purposes.
In the early days of telephony great difficulty was experienced in using
a single wire grounded at each end in the ordinary way, if it ran near
other wires that were in active use. As time passed on and the electric
light and electric railroad came into operation these difficulties were
immensely increased, till now in large cities the telephone companies
are fast being driven to the double-wire system, which will soon become
universal for telephonic purposes the world over, except perhaps in a
few country places where there is freedom from other systems of
electrical transmission. To successfully work the telephone and
telautograph through the same cables, these protective devices against
induction must be very carefully provided and maintained.