Experiments in telegraphy were carried out as far back as the year 1753,
when it was proposed to transmit messages by representing the letters of
the alphabet by combinations of sparks produced by a static machine; but
these were of little practical value and nothing of any importance was
accomplished until after the discovery of galvanic current.
Many of these old experiments were very crude and appear somewhat
ridiculous when compared with the methods of nowadays. The earliest
proposal for an electric telegraph appeared in the _Scots’ Magazine_ for
February, 1753, and shows several kinds of proposed telegraphs acting by
the attractive power of electricity, conveyed by a series of parallel
wires, one wire corresponding to each letter of the alphabet and
supported by glass rods at every twenty yards. Words were to be spelled
by the action of the electricity in attracting paper letters, or by
striking bells corresponding to letters.
The modern telegraph consists essentially of four things, namely:
A battery which produces an electric current.
A wire which conducts the electric current from one point to another.
A transmitter for shutting the current off and on.
An electro-magnetic receiving apparatus, which gives out in sounds, the
signals made by the pulsations of the current from a distant point.
The battery may be almost any form of battery. Gravity cells are
preferred, however, for telegraph work.
Heavy galvanized iron wire is usually employed as the "line." It is
necessary to use non-conductors wherever the wire is fastened. Glass
insulators placed on a wooden pin or bracket, which is fastened to the
pole or building on which the wire is to be supported, are used for
outside work. Inside of buildings, rubber tubes are used where the wires
pass through walls, etc.
The operation of a telegraph is not, as many people suppose, a
complicated or difficult matter to understand, but is quite simple.
The key is a contrivance for controlling the passage of the electric
current in much the same manner as an ordinary switch. It consists of a
steel lever, swung on trunnion-screws mounted in a frame, and provided
with a rubber knob which the operator grasps lightly with the thumb and
forefinger. On pressing the lever downward, a platinum point fastened on
the under side of the lever is brought into contact with another point
set into a rubber bushing in the base of the key, so that there is no
electrical connection between the two points unless the key is pressed
down or "closed," as it is often termed. The key is usually fastened to
the operating bench by two rods called "legs." The lever is provided
with screws which permit the stroke of the key to be very closely
adjusted.
[Illustration: Fig. 130.—A Typical Telegraph Key, showing the Various
Parts.]
The line wire and battery are connected to the key, so that no current
can flow until the key is pressed and the contacts brought together.
A "sounder" consists of two electromagnets mounted on a base under a
movable flat piece of iron which is attracted by the magnetism of the
electromagnets when a current flows through them and is withdrawn by a
spring when no magnetism excites the windings.
This piece of iron, which is called the armature, is mounted upon a
strip of brass or aluminum called the lever. The lever strikes against a
brass "anvil" and produces the "clicks," which form the dots and dashes
of the telegraph alphabet.
[Illustration: Fig. 131.—A Typical Telegraph Sounder, showing the
Various Parts.]
Every time that the key is pressed, an electric current is sent out into
the line. The current flows through the magnets of the sounder and
causes the armature to be drawn downward. The lever strikes the anvil
and produces a "click." When the key lever is released, the current is
shut up and the lever flies up and clicks against the top of the anvil.
The period of time between the first click and the second click may be
varied at will according to the length of time that the key is held
down. A short period is called a _dot_ and a long period a _dash_.
Combinations of dots, dashes, and spaces arranged according to the Morse
Alphabet, make intelligible signals.
How To Make a Simple Key and Sounder
The little telegraph instruments shown in Figures 132 and 133 are not
practical for long lines but may be used for ticking messages from one
room to another, and can be made the source of much instruction and
pleasure.
[Illustration: Fig. 132.—A Simple Home-made Telegraph Key.]
The key is a strip of brass fastened to a wooden base in the manner
shown in Figure 132. It is fitted with a knob of some sort on the front
end, so that it is conveniently gripped with the fingers.
The little bridge is made from heavy sheet-brass and prevents the lever
from moving too far away from the contact on the upward stroke.
Connections are made to the key lever at the back end and the contact in
front by the binding-posts, _A_ and _B_. The post, _C_, connects with
the bridge.
The sounder consists of two small electromagnets mounted in a vertical
position on a wooden base. The magnets are connected at the bottom by a
strip of heavy sheet-iron which acts as a yoke.
[Illustration: Fig. 133.—A Simple Home-made Telegraph Sounder.]
The armature is made out of sheet-iron, rolled up in the manner shown in
the illustration. One end of the armature is fastened to a wooden block
in such a position that the armature comes directly over the magnets and
about one-eighth of an inch above them. The opposite end of the armature
moves up and down for about an eighth of an inch between two screws,
each fastened in a wooden block mounted on an upright board in the back
of the magnets. The purpose of the screws is to make the "click" of the
sounder louder and clearer than it would be if the armature only struck
the wood.
A rubber band or a small wire spring passing over a screw and connected
at the other end to the armature will draw the latter away from the
magnets when the current is not passing.
The terminals of the magnets are connected to binding-posts mounted on
the base.
[Illustration: Fig. 134.—A Diagram showing how to connect two Simple
Telegraph Stations.]
The key and sounder should be placed in series with one or two cells of
a battery. Pressing the key will then cause the armature of the sounder
to be drawn down and make a click. When the key is released, the
armature will be drawn up by the spring or rubber band and make a second
click.
Hardly a boy interested in mechanics and electricity has not at some
time or other wished for a telegraph instrument with which to put up a
"line" with his chum.
A practical working set of such instruments can be very easily
constructed, and with little expense, by following the sketches and
instructions given here.
The magnets for the sounder may either be constructed by the intending
telegraph operator or secured from some old electrical instrument such
as a magneto-bell. In the latter case, the hardest part of the work will
be avoided.
If they are to be home-made, the following suggestions may prove of
value in carrying out their construction.
[Illustration: Fig. 135.—A Complete Telegraph Set, consisting of a
Keyboard and a Sounder.]
The cores are made from one-quarter-inch stove-bolts with the heads cut
off. The magnet heads are cut out of hard-wood fiber, one-eighth of an
inch thick and one inch in diameter. They should fit tightly and be held
in place with glue. They are separated so as to form a winding space
between of seven-eighths of an inch. The magnets should be wound full of
No. 25 B. & S. gauge cotton-covered wire.
[Illustration: Fig. 136.—Details of the Telegraph Set shown in Figure
135.]
The yoke is made of enough strips of sheet-iron, one-half inch wide and
two inches long, to form a pile one-quarter of an inch thick. Two
one-quarter-inch holes are bored in the opposite ends of the yoke, one
and one-half inches apart. The lower ends of the magnet cores are passed
through these holes. The ends should project one-half of an inch beyond
the yoke.
They are passed through two holes in a base-board three-quarters of an
inch thick. The holes are countersunk from the lower side, so that a nut
can be screwed on the lower end of each and the magnets held tightly in
an upright position. The remaining parts of the instrument are very
easily made, and are so clearly shown by the drawing that it is hardly
necessary to say more than a few words in explanation.
The lever or tongue, the anvil, the standard, and the lever of the key
are all cut out of hard-wood according to the pattern shown in the
illustration.
The armature is a piece of soft iron fastened to the lever with a small
brass screw.
Tacks are placed under the heads of the adjusting screws on the sounder
so that it will click more loudly.
The rubber band acts as a spring to counteract the weight of the
armature and lever and draw it up as soon as the current is cut off. The
movement of the lever should be so adjusted that it is only sufficient
to make an audible click.
Use care to avoid friction between the lever and the standard, so that
the former will move with perfect freedom.
All the screws used in the work should be round-headed brass wood screws
with the points filed flat. Bore a small hole before screwing them into
place so as to avoid splitting the wood.
The construction of the key is even more simple than that of the
sounder. It should move up and down without any side motion.
The circuit-closer should be kept closed when the instruments are not in
use, and when you are receiving a message. As soon as you are through
receiving and wish to transmit, you should open your circuit-closer and
your friend close his.
The tension of the spring under the lever of the key must be adjusted to
suit the needs of each individual operator.
[Illustration: Fig. 137.—A Diagram showing how to connect two Complete
Telegraph Sets, using one Line Wire and a Ground. The Two-Point Switches
throw the Batteries out of Circuit when the Line is not in use.]
The diagram for connecting the instruments is self-explanatory. In
cities or towns where a "ground" is available by connecting to the gas
or water pipes, one line wire may be easily dispensed with. Or, if
desirable, a ground may be formed by burying a large plate of zinc
(three or four feet square) in a moist spot and leading the wire to it.
How To Build a Telegraph Relay
In working a telegraph over a long line or where there are a large
number of instruments on one circuit, the currents are often not strong
enough to work the sounder directly. In such a case a _relay_ is used.
The relay is built on the same principle as a sounder, but the parts are
made much lighter, so that the instrument is more sensitive. The
armature of a relay is so small and its movement so little that its
clicking is scarcely audible. It is therefore fitted with a second set
of contacts and connected to a battery and a sounder, which is to set in
operation every time the contacts close. The principle of a relay is
that a weak current of insufficient strength to do the work itself may
set a strong local current to do its work for it.
There are many forms of relays, and while that which is described below
is not of the type commonly used on telegraph lines, it has the
advantage of being far more sensitive than any instrument of the regular
line relay type that the average experimenter could build.
[Illustration: Fig. 138.—Details of the Relay Parts.]
Make the magnets from one-quarter-inch stove-bolts, and cut them off so
that they will form a core about two and one-quarter inches long. Fit
each of the cores with two fiber heads to hold the wire in place.
Insulate the legs with paper and wind each with about fifty layers of
No. 30 B. & S. gauge single-cotton-covered magnet wire. The winding
space between the magnet’s heads should be one and one-eighth inches.
The upper ends of the magnet cores should be allowed to project about
one-quarter of an inch beyond the fiber head. The end of the core is
filed flat, as shown in the illustration.
The magnets are mounted upon an iron yoke, three-sixteenths of an inch
thick. The holes in the yoke should be spaced so that there is a
distance of one and one-half inches between the centers of the magnet
cores.
The armature of the relay is mounted on a small steel shaft with sharp
points at each end. The exact shape of the armature may be best
understood from the illustrations.
The lower end of the shaft rests in a small cone-shaped depression made
by driving a center punch into the yoke half-way between the two
magnets.
The top bearing is a strip of brass projecting from a wooden support.
The end of the shaft rests in a depression similar to that in the yoke.
The contact lever is made of brass and forced on the shaft below the
armature. It swings between a small brass clip fastened to one side of
the support and a little screw held in a similar clip on the opposite
side.
The contact clip is made of spring brass about No. 22 gauge in
thickness. It may be adjusted by a screw passing through the support.
The armature may be controlled in its movement so that the latter will
be very slight by adjusting the screws.
There should not be any friction in the bearings and the armature should
move with perfect freedom. The armature should approach the ends of the
magnet cores until a space about the thickness of heavy paper separates
them and should not touch them.
[Illustration: Fig. 139.—The Completed Relay.]
The spring is made of fine brass wire. It is fastened to the armature
shaft, and the screw mounted on the wooden support with a piece of silk
thread. The thread is passed around the shaft once or twice so that the
tension of the spring will cause the armature to move away from the pole
pieces just as soon as the current flowing through the magnets ceases.
[Illustration: Fig. 140.—A Diagram showing how to connect a Relay,
Sounder, and Key. Closing the Key will operate the Relay. The Relay will
then operate the Sounder in turn.]
The tension of the spring may be adjusted by turning the screw with a
screw-driver. If the armature tends to stick to the magnet poles fasten
a small piece of paper to the poles with some shellac.
The terminals of the magnets are connected to two binding-posts marked
_A_ and _B_. The binding-posts marked _C_ and _D_ are connected
respectively to the contact clip and the brass bearing on the top of the
wooden support.
The diagram in Figure 140 shows how the relay is connected to a
telegraph line.
How To Learn To Telegraph
The instruments so far described have been practical working telegraph
instruments, but they lack the fine points of commercial apparatus and
it is not possible to become as efficient an operator with their aid as
with a real key and sounder.
If the young experimenter desires to become a proficient telegraph
operator, the first thing to do is to purchase a Learner’s telegraph key
and sounder.
Connect a dry cell to the binding-posts on the back of the instrument.
Screw the set down on a table about eighteen inches from the front edge,
so that there is plenty of room for the arm to rest. See that none of
the various adjustment screws about the instrument are loose and that
the armature of the sounder moves freely up and down through a distance
of about one-sixteenth of an inch.
The spring which draws the lever upwards away from the magnets should be
set only at sufficient tension to raise the lever when no current is
passing. If too tight, the spring will not allow the armature to respond
to the current flowing through the magnets.
The key is provided with several adjustment-screws to regulate the
tension and the play of the lever to suit the hand of the operator. A
little practice will enable the student to judge best for himself just
how the key should be set.
The next step is to memorize the alphabet, so that each character can
instantly be called to mind at will. The punctuation marks are not used
very frequently, and the period is the only one which the student need
learn at first.
The Morse alphabet consists of dots, dashes, and spaces. Combinations of
these signals spell letters and words.
Many of the characters are the reverse of others. For example, _A_ is
the reverse of _N_. _B_ and _F_, _D_ and _U_, _C_ and _R_, _Q_ and _X_,
_Z_ and _&_, are the other reverse letters, so if the formation of one
of each of these letters is memorized the reverse is easily mastered.
It is important that the beginner should learn how properly to grasp the
key, for habits are easily formed and a poor position will limit the
sending speed of the operator.
Place the first or index finger on the top of the key-handle, with the
thumb under the edge; and the second finger on the opposite side. The
fingers should be curved so as to form a quarter-section of a circle.
Bring the third and fourth fingers down so that they are almost closed
on the palm of the hand. Rest the arm on the table in front of the key
and allow the wrist to be perfectly limber.
[Illustration: Fig. 141.—How to hold a Telegraph Key.]
The grasp on the key should be firm but not rigid. Avoid using too much
strength or a light hesitating touch. Endeavor to acquire a positive,
firm up and down motion of the key. Avoid all side pressure, and do not
allow the fingers to leave the key when making the signals. The movement
is made principally with the wrist, with the fingers and hand perfectly
elastic.
A dot is made by a single instantaneous, downward stroke of the key. A
dash is made by holding the key down for the same period of time that it
takes to make three dots. A long dash is made by holding the key down
for the same time that it takes to make five dots.
A space in the letters, such as, for instance, the space between the
first and last two dots in the letter _R_ should occupy the time of one
dot. The space between each letter should occupy the time required for
two dots, and the space between words should occupy the time required
for three dots.
Commence the use of the key by making dots in succession, first at the
rate of two every second, and increasing the speed until ten can be
made. Practice should be continued until three hundred and sixty dots a
minute can be made with perfect regularity.
Then begin making dashes at the rate of two every three seconds, and
continue until one hundred and twenty a minute can be made with perfect
regularity.
Practise the long dashes at the rate of one a second, and increase until
ninety can be made in a minute.
[Illustration: Fig. 142.—The Morse Telegraphic Code.]
When this has been accomplished, practise the following letters until
they can be perfectly made. Each row of letters is an exercise which
should be practised separately until mastered.
Dot Letters
E I S H P 6
Dot and Space Letters
O C R Y Z &
Dash Letters
T L M 5 O
Dots and Dashes
A U V 4
Dashes and Dots
N D B 8
Mixed Dots and Dashes
F G J K Q W X 1 2 3 7 9 Period
After you can write these different letters, practise making words.
Select a list of commonly used words. When words seem easy to write,
practise sending pages from a book.
Systematic and continual practice will enable the student to make
surprising progress in mastering the art of sending.
Reading and receiving messages must be practised with a companion
student. Place two instruments in separate rooms or in separate houses
so that the operators will be entirely dependent upon the instruments
for their communication with each other. Start by transmitting and
receiving simple messages. Then use pages from a book, and increase the
speed until it is possible to send and receive at least 15 words a
minute without watching the sounder but merely depending upon the clicks
to determine the duration of the dots and dashes.
Figure 140 shows how to arrange a regular telegraph line for two
stations. Gravity batteries should be used for regular telegraph work.
It is necessary that the key should be kept closed by having its
circuit-closer shut when messages are not being sent. If one of the keys
is left open the circuit is broken, and it is not possible for a person
at the other end of the line to send a message.
Every telegraph office has a name or call usually consisting of two
letters; thus for New York the call might be N. Y. and for Chicago, C.
H.
If New York should desire to call Chicago, he would repeat the call
letters, C H., until answered. Chicago would answer by sending I,
several times and signing, C H. When so answered, New York would proceed
with the message.