THE ELECTRIC TELEGRAPH
WHEN two persons engage in ordinary conversation, they
really use two methods of communication. Both methods are extremely
complicated. By means of mouth, tongue, and throat, the speaker
changes the current of air issuing from his lungs, and throws it into
a great variety of vibrations. These vibrations are communicated to
the outside air and find their way into the ears of the other person.
Such is speech. At the same time, people when speaking employ signals
which appeal to the eye. They move their lips, eyelids, eyebrows, and
sometimes their hands, and each motion gives a slightly different
quality, or stress, to what they are saying. These motions produce an
effect upon the waves of light which are constantly passing to and fro
between the two people. In this way speech is assisted by sight.
When two persons are far apart and still wish to communicate they have
to shout. When the distance becomes greater, their voices become less
and less able to cover it, and, finally, they are driven to communicate
by sight only. So, we find them waving their hands, or handkerchiefs,
or hags at the end of sticks. When the distance is many miles, this
method fails again, and communication becomes very difficult. In
ancient times people used to get out of the difficulty by lighting
big fires which could be seen for ten or fifteen miles in the dark.
The smoke from the fire could be seen for about the same distance in
the day-time. Some savage tribes use the same method even now, and
manage to convey a great deal of information by it. But nowadays we
use the electric telegraph for all such purposes, and the story of its
invention is one of great interest.
The immediate predecessor of the electric telegraph was the optical
telegraph invented by Hooke, Newton’s assistant. The first occasion
on which the optical telegraph was put to practical use was about the
time of the French Revolution. In the year 1792 the whole of France
was covered by a system of signals. The system consisted of a number
of towers on the top of which “semaphores” were mounted which looked
very much like the railway signals of the present day. By means of this
system a message could be sent from Paris to the end of France in a few
hours. When the war broke out in Austria in 1809, the great Napoleon
profited by it to fall upon the Austrians unawares, giving them no time
to make preparations to meet him.
[Illustration: Fig. 52.--Optical Telegraph.]
The Austrians were in alliance with the Bavarians, who suffered greatly
by the war with Napoleon, and the Bavarian Government asked one of
the professors at Munich to devise a system of telegraphy which should
be superior to that used so successfully by Napoleon. The name of the
professor was Soemmering.
[Illustration: Fig. 53.--Soemmering’s First Electric Telegraph.]
He started on the work at once, and four days after receiving the
request he had devised the first electric telegraph which was capable
of transmitting the letters _a_, _b_, _c_, _d_,
_e_. That was all. The apparatus was quite simple and very
ingenious. It consisted of one of Volta’s piles made of fifteen pairs
of silver and iron plates separated by layers of felt soaked in salt
water.
This arrangement was the source of electricity. At the station to which
the signals were to be sent there was a bottle or small tank of water
with a large cork in the bottom of it. Through this cork five wires
were drawn, and they led into water with which the bottle was filled.
The five wires were made very long. They were covered with shellac
varnish, and then they could be twisted together without being in
actual contact. The strand of wire was stretched between the sending
station and the receiving station.
At the sending station the strand of wire was unravelled, and the five
loose ends were marked with the letters _a_, _b_, _c_,
_d_, _e_. The top of the Volta pile placed at the sending
station gave positive electricity, and the bottom of the pile gave
negative electricity. Now, suppose that the wire marked _a_ was
brought into contact with the top of the pile, and the wire marked
_b_ was brought into contact with the bottom of the pile. Then
an electric current travelled all along the strand, through the pile
and the two wires, and through the water between the two wires, thus
making a complete circuit. The water in the bottle was then split up
into hydrogen and oxygen, and bubbles of hydrogen appeared at the wire
_b_ where it entered the water. The observer at the receiving
station then understood that his companion at the sending station
wanted to telegraph to him the letter _b_.
Whenever the man at the sending station wanted to telegraph a letter,
all he had to do was to bring the corresponding wire into contact with
the bottom of the pile, and to bring any other wire into contact with
the top of the pile. The wire at the top was usually the wire which
came next in the message, so that the two letters could be telegraphed
at the same time, the second letter being that which gave off a very
small quantity of oxygen gas.
The instrument so constructed was only capable of sending five
different letters. In order to send a complete message, it was
necessary to have as many wires as there are letters in the alphabet.
Twenty-six wires were therefore twisted together in a strand, after
being covered with varnish and silk thread. The ends of the wires at
the sending station were nailed to a frame by means of nails with
perforated heads. A wire was kept touching the top of the Volta pile,
and another was kept in contact with the lower end of the pile.
These wires ended in small plugs which could be inserted into the
perforations of the nails, so that the sender could pick out any two
letters he wished to telegraph. At the other end the wires were laid
through the bottom of a vessel containing water, and were marked
with appropriate letters. The telegraph was then worked on the same
principle as the smaller one made for five letters.
In addition to these letters, the inventor devised a mechanism by
which a bell could be sounded in order to attract the attention of the
man at the receiving end. This apparatus was extremely ingenious. It
consisted of a lever to which a spoon was attached.
[Illustration: Fig. 54.--Soemmering’s Telegraph.]
The spoon lay in the water, just above two of the wires, with its open
surface down. When the current was sent through these two wires, the
hydrogen and oxygen collected in the spoon, and raised it. This set a
little ball rolling down into a funnel. Through the funnel it dropped
into a small pan, and removed the catch of an alarm clock. This set the
alarm going and attracted the attention of the man at the receiving
station. When the message was finished, the man had to put back the
ball to its original place, and wind up and set the alarm clock as
before.
It was not long before the Emperor Napoleon heard of the Bavarian
invention. One of his officials told him about it and asked leave to
explain it to him. The Emperor listened to the explanation, but then
swept it aside as worthless. “It’s only a German idea,” he said. He
considered it impossible to lay a strand of wire across country and to
preserve it from damage. He preferred to rely on his optical telegraph
which had done him such good service.
The electric telegraph did not come into real use until the magnetic
needle was adopted as an indicator. Ten years after the first telegraph
was invented, a Danish electrician made a very important discovery,
which exercised a far-reaching effect upon electric science. He was
trying to discover some connection between electricity and magnetism,
and made all sorts of experiments with magnetic compasses. He found
at last that a magnetic needle is affected powerfully by a current
passing in a wire close by. When a wire bearing an electric current is
stretched along a table from north to south, and a magnetic compass
is placed on the top of the wire pointing in the same direction, the
needle swings round every time the current is sent through the wire,
and swings back into its ordinary position as soon as the current is
interrupted. So long as the current flows, the needle tends to set
itself at right angles to the wire, and will do so almost exactly when
the current is very strong.
This discovery made a great impression on the scientific world, and
many men of science proposed to use it for the purpose of telegraphy.
But it was not until the year 1833 that the first telegraph was
constructed on this principle. Two professors in Heidelberg, whose
names were Gauss and Weber, established a telegraph of this kind
between the Physical Institute and the Observatory. The wire had a
total length of nearly two miles, and they produced at the receiving
station a deflection of a magnetic needle to the right or left. This
arrangement was afterwards improved by a young student, who attached
pens to two magnetic needles, and made them write dots on a strip
of paper passing along under them. Using two different inks, he got
different sets of coloured dots for each letter. These could be easily
recognised afterwards and read off the paper.
The current used in these experiments was not a steady current from a
Volta pile or electric battery. It was a so-called induction current.
The induction current had been discovered in 1831 by a great Englishman
of the name of Michael Faraday, who found that when a wire is placed
by the side of another wire through which electricity can pass, then as
soon as the current is sent through this wire by connecting it with the
battery, a momentary current flows in the opposite direction through
the other wire.
[Illustration: Fig. 55.--Diagram of Morse System of Telegraphy.]
For this to happen, however, it is necessary that the second wire
should also form a closed circuit, and not have any free ends. Such an
induction current, or induced current, can also be obtained by means
of a large magnet. All that is necessary is to take a coil of wire and
suddenly slip it upon a bar magnet, or suddenly slip it off. The more
rapidly the slipping on or off is done the stronger is the current.
In this way, therefore, it is possible to produce an electric current
without any piles, or batteries, or chemicals.
[Illustration: Fig. 56.--S. F. B. Morse.]
This kind of current was found very effective for telegraphy,
especially as the magnet was always ready, whereas the electric
batteries, or cells, were liable to get exhausted and useless. It was
only when the electric battery was improved greatly and made more
trustworthy that it was adopted again for telegraphy, and it is used
for that purpose at the present day.
A great improvement was introduced into telegraphy by S. E. B. Morse,
who invented the alphabet known as the “Morse Code” and also a
recording machine which writes down the message in dots and dashes. The
alphabet is as follows:--
a • — h • • • • o — — — u • • —
b — • • • i • • p — — • v • • • —
c — • • • • j • — — — q — — • — w • — —
d — • • k — • — r • — • x — • • —
e • l • — • • s • • • y — • — —
f • • — • m — — t — z — — • •
g — — • n — •
[Illustration: Fig. 57.--The Needle Telegraph.]
The word “alphabet” appears on the paper strip like this:--
• — • — • • — — • • • • • • — — • • • • —
a l p h a b e t
For work in which no record is required, the needle telegraph is
employed usually. But the Morse code is used in this case also, the
needle moving to the right when a dot is intended, and to the left when
a dash. Telegraph clerks get after a while to understand a message by
simply listening to the sound of the needle. Nowadays the needle is a
stout magnet, which as a rule rests against a piece of iron belonging
to an electromagnet. When the current passes, it knocks against a
different piece of iron, and the operators learn to read the message
from the sound of the knocks. The instrument is therefore called a
_sounder_.