HOW THE TELEPHONE TALKS.
Everybody knows what the telephone is because it is in almost every
man's house. But while everybody knows what it is, there are very few
(comparatively speaking) that know how it works. If you remember what
has been said about sound and electromagnetism it will not be hard to
understand.
When any one utters a spoken word the air is thrown into shivers or
vibrations of a peculiar form, and every different sound has a different
form. Therefore, every articulate word differs from every other word,
not only as a shape in the air, but as a sensation in the brain, where
the air-vibrations have been conducted through the organ of hearing;
otherwise we could not distinguish between one word and another. Every
different word produces a different sensation because there is a
physical difference, as a shape or motion, in the air where it is
uttered. If one word contains 1000 simultaneous air-motions and another
1500 you can see that there is a physical or mechanical difference in
the air.
The construction of the simplest form of telephone is as follows: Take a
piece of iron rod one-half or three-quarters of an inch long and
one-quarter inch thick, and after putting a spool-head on each end to
hold the wire in place wind it full of fine insulated copper wire;
fasten the end of this spool to the end of a straight-bar permanent
magnet. Then put the whole into a suitable frame, and mount a thin
circular diaphragm (membrane or plate) of iron or steel, held by its
edges, so that the free end of the spool will come near to but not touch
the center of the diaphragm. This diaphragm must be held rigidly at the
edges.
Now if the two ends of the insulated copper wires are brought out to
suitable binding-screws the instrument is done.
The permanent steel magnet serves a double purpose. When the telephone
was first used commercially, the instrument now used as a receiver was
also used as a transmitter. As a transmitter it is a dynamo-electric
machine. Every time the iron diaphragm is moved in the magnetic field of
the pole of the permanent magnet, which in this case is the free end of
the spool (the iron of the spool being magnetic by contact with the
permanent magnet), there is a current set up in the wire wound on the
spool; a short impulse, lasting only as long as the movement lasts. The
intensity of the impulse will depend upon the amplitude and quickness
of the movement of the diaphragm. If there is a long movement there will
be a strong current and vice versa. If a sound is uttered, and even if
the multitude of sounds that are required to form a word, be spoken to
the diaphragm, the latter partakes in kind of the air-motions that
strike it. It swings or vibrates in the air, and if it is a perfect
diaphragm it moves exactly as the air does, both as to amplitude and
complexity of movement. You will remember that in the chapter on
sound-quality (Vol. II) it was said that there were hundreds and
sometimes thousands of superposed motions in the tones of some voices
that gave them the element we call quality.
All these complex motions are communicated by the air to the diaphragm,
and the diaphragm sets up electric currents in the wire wound on the
spool, corresponding exactly in number and form, so that the current is
molded exactly as the air-waves are. Now, if we connect another
telephone in the circuit, and talk to one of them, the diaphragm of the
other will be vibrated by the electric current sent, and caused to move
in sympathy with it and make exactly the same motions relatively, both
as to number and amplitude.
It will be plain that if the receiving diaphragm is making the same
motions as the transmitting diaphragm, it will put the air in the same
kind of motion that the air is in at the transmitting end, and will
produce the same sensation when sensed by the brain through the ear. If
the air-motion is that of any spoken word it will be the same at both
ends of the line, except that it will not be so intense at the
receiving-end; it is the same relatively. And this is how the telephone
talks.
I have said that the permanent magnet had two functions. In the case of
the transmitter it is the medium through which mechanical is converted
into electrical energy. It corresponds to the field-magnet of the
dynamo, while the diaphragm corresponds to the revolving armature, and
the voice is the steam-engine that drives it. In the second place, it
puts a tension on the diaphragm and also puts the molecules of the iron
core of the magnet in a state of tension or magnetic strain, and in that
condition both the molecules and the diaphragm are much more sensitive
to the electric impulses sent over the wire from the transmitter. This
fact was experimented upon by the writer as far back as 1879 and
published in the Journal of the American Electrical Society. At the
present day this form of telephone is used only as a receiver.
Transmitters have been made in a variety of forms, but there are only
two generic methods of transmission. One is the magneto method--the one
we have described--and the other is effected by varying the resistance
of a battery current. The former will work without a battery, as the
voice acting on the wire around the magnet through the diaphragm creates
the current; in the latter the current is created by the battery but
molded by the voice. In the latter method the current passes through
carbon contacts that are moved by the diaphragm. Carbon is the best
substance, because it will bear a wider separation of contact without
actually breaking the current. When carbon points are separated that
have an electric current passing through them, there is an arc formed on
the same principle as the electric arc-light.
Great improvements in details have been made in the telephone since its
first use, but no new principles have been discovered as applied to
transmission.
We have spoken in another place regarding the various claimants to the
invention of the telephone, but here is one that has been overlooked. A
young man from the country was in a telegraph-office at one time and was
left alone while the operator went to dinner. Suddenly the sounder
started up and rattled away at such a rate that the countryman thought
something should be done. He leaned down close to the instrument and
shouted as loudly as possible these words: "The operator has gone to
dinner." From what we know now of the operation of the telephone I have
no doubt but that he transmitted his voice to some extent over the wire.
This young man's claims have never been put forward before, and we are
doing him tardy justice. But his claim is quite as good as many others
set forth by people who think they invent, whenever it occurs to them
that something new might possibly be done, if only somebody would do it.
And when that somebody does do it they lay claim to it.
In the early days of the telephone it was not supposed that a vocal
message could be transmitted to a very great distance. However, as time
went on and experiments were multiplied the distance to which one could
converse with another through a wire kept on increasing.
In these days, as every one knows, it is a daily occurrence that
business men converse with each other, telephonically, for a distance of
1000 miles or more; in fact, it is possible to transmit the voice
through a single circuit about as great a distance as it is possible to
practically telegraph. This leads us to speak of another telegraphic
apparatus which we have not heretofore mentioned, and that is the
telegraphic repeater. It is a common notion that messages are sent
through a single circuit across the continent, but this is not the
case, although the circuits are very much longer than they were some
years ago. The repeater is an instrument that repeats a message
automatically from one circuit to another. For instance, if Chicago is
sending a message to New York through two circuits, the division being
in Buffalo, the repeater will be located at Buffalo and under the
control of both the operator at Chicago and the operator in New York.
When Chicago is sending, one part of the repeater works in unison with
the Chicago key and is the key to the New York circuit, which begins at
Buffalo. When New York is sending the other part of the repeater
operates, which becomes a key which repeats the message to the Chicago
line. In this way the practical result is the same as though the circuit
were complete from New York to Chicago. At the present day some of the
copper wires and perhaps some of the larger iron wires are used direct
from Chicago to New York without repetition, but all messages between
New York and San Francisco are automatically repeated at least twice and
under certain conditions of weather oftener. I can remember that in wet
weather in the old days, with such wires as they had then (being No. 9
iron with bad joints, which gave the circuit a high resistance) that
these repeaters would be inserted at Toledo, Cleveland, Buffalo and
Albany in order to work from Chicago to New York. Under such conditions
the transmission would necessarily be slow, because an armature time
will be lost at each repeater. Regarding each repeater as a key, when
Chicago depresses his key the armature of the next repeater must act,
and then the next successively, and all of this takes time, although
only a small fraction of a second.
The repeater was a very delicate instrument and had to be handled by a
skilled operator. Every wire must be in its place or the instrument
would fail to operate. I remember on one occasion in Cleveland that
along in the middle of the night the repeater failed to work. The
operator knew nothing of the principle of its operation, so that when it
failed he had to appeal to some of his superiors.
At this time there was no one in the office who knew how to adjust it,
so they had to send up to the house of the superintendent and arouse him
from his sleep and bring him down to the office. He looked under the
table and found that one of the wires had loosened from its binding-post
and was hanging down. He said immediately, "Here's the trouble; I should
think you could have seen it yourself." The operator replied, "I did see
that, but I didn't think one wire would make any difference." He learned
the lesson that all electricians have had to learn--that even one wire
makes all the difference in the world. But this operator was no worse
in that respect than some of his superiors. One of the heads of the
Cleveland office at one time in the early days wanted to give some
directions to the office at Buffalo. He told the operator at the key to
tell Buffalo so and so, when the operator replied: "I can't do it;
Buffalo has his key open." The official immediately said with severity:
"Tell him to close it." He forgot that it would be as difficult for him
to tell him to close it, as it would have been to have sent the original
message.
But let us go back to the telephone. While it is possible to send a
message from New York to San Francisco by telegraph, it is not possible
to telephone that distance, because as yet no one has been able to
devise a repeater that will transfer spoken words from one line to
another satisfactorily. But unless the printer and publisher bestir
themselves some one may accomplish the feat before this little book
reaches the reader. If this proves to be true, let the writer be the
first to congratulate the successful inventor.