United States Government is also extremely simple, communicating its
signals, not by the deflections of a needle, but by the blows on an
electro-magnet of its armature. The letters are indicated by various
combinations of two signals—one, a single stroke of the armature; and
the other, two blows in very rapid succession. The alphabet used is the
“General Service Flag Code” of the American army and navy, and the
signal numerals of this code are indicated by contacts of the
transmitting key—one contact producing a single blow of the armature,
implying the numeral 1, and two rapidly succeeding contacts causing two
blows, which stand for the numeral 2. The signals are read merely by the
sound made by the stroke of the armature. In the table below the code is
given, dots being used to represent the contacts of the key in the
“sending” instrument, and the blows of the armature in the “receiving”
instrument—the single dots standing for one contact or sound, and the
double dots for the double blows:
┌────────┬──────────┬────────────────────┐
│Letters.│Flag Code.│ Telegraph Signals. │
├────────┼──────────┼────────────────────┤
│ A │2 2 │·· ·· │
│ B │2 1 1 2 │·· · · ·· │
│ C │1 2 1 │· ·· · │
│ D │2 2 2 │·· ·· ·· │
│ E │1 2 │· ·· │
│ F │2 2 2 1 │·· ·· ·· · │
│ G │2 2 1 1 │·· ·· · · │
│ H │1 2 2 │· ·· ·· │
│ I │1 │· │
│ J │1 1 2 2 │· · ·· ·· │
│ K │2 1 2 1 │·· · ·· · │
│ L │2 2 1 │·· ·· · │
│ M │1 2 2 1 │· ·· ·· · │
│ N │1 1 │· · │
│ O │2 1 │·· · │
│ P │1 2 1 2 │· ·· · ·· │
│ Q │1 2 1 1 │· ·· · · │
│ R │2 1 1 │·· · · │
│ S │2 1 2 │·· · ·· │
│ T │2 │·· │
│ U │1 1 2 │· · ·· │
│ V │1 2 2 2 │· ·· ·· ·· │
│ W │1 1 2 1 │· · ·· · │
│ X │2 1 2 2 │·· · ·· ·· │
│ Y │1 1 1 │· · · │
│ Z │2 2 2 2 │·· ·· ·· ·· │
└────────┴──────────┴────────────────────┘
There are similar signals for the numerals and for a few often-recurring
syllables.
The telegraphs we have hitherto described leave no record of the
despatches sent, and hence the messages cannot be read at leisure, and
errors which may occur in the transmission cannot be traced to their
source. A system which registers the messages as actually received has
plainly many advantages over those which merely give a visible or
audible signal without leaving any trace. Hence many contrivances have
been proposed for making the receiving apparatus print the message in
ordinary characters. Such instruments are necessarily very much more
complicated in their construction than those we have already mentioned,
and by no means so simple as the system we are about to describe,
namely, the Morse Telegraph, which is now so largely used, being
universally adopted in America and on the continent of Europe; and,
since the telegraphic communication in Great Britain came into the hands
of the Post-office authorities, here, also, the Morse is the system most
approved.
[Illustration:
FIG. 285.—_Connections of a Telegraphic Line, with Morse Instruments._
]
The general arrangement of the transmitters, batteries, receiving
instruments, &c., should be first studied in its simplest form, as
represented by the diagram, Fig. 285. M represents the vertical coils of
an electro-magnet upon which we are supposed to be looking down; the
armature, A, is attached to a lever, F, which, by the attraction of the
electro-magnet is therefore drawn down. In the position of the
connections, as represented, no current is passing, but if K be pressed
down so as to make connection at 1, at the same time it is broken at 2,
a current will pass in from the positive pole of battery, B, into the
line by 1, 3, L, L´, and through 3´, 2´ through the coils of the
electro-magnet at M´ into the earth, and so back to the negative pole,
Z. The armature, A´, will be attracted so long as the current continues.
Similarly, contact made at 1´ and broken at 2´, will affect the
electro-magnet, M, from the battery at B´. It should be noticed here
that it is not a question of the reversal of currents sent from the same
battery; the key merely enables the operator to send a current in one
direction, so as to affect the distant electro-magnet whenever or so
long as he depresses the key. We shall now examine the construction of
the Morse receiving apparatus, one of the most complete forms of which
is depicted in Fig. 286. In the present description we wish the reader
to consider only the portion of the apparatus towards the left, and to
suppose the absence of the electro-magnet at the right-hand side, with
all the appliances immediately connected with it. He must regard the
electro-magnet, A, as corresponding with M´ in Fig. 285, and remember
that it is in the power of the distant operator at K to throw the
current of his battery through the coils of A, by simply depressing his
key. When the current passes the armature, B, it is attracted, and the
lever, C, to which it is attached, turns on its bearings at D, and the
end, E, of its longer arm is pressed upwards. At this end of the lever,
in the earlier form of the instrument, was a blunt steel point which,
while the armature was attracted to the electro-magnet, was pressed into
a shallow groove in a metallic roller. Between the roller and the steel
point a paper ribbon, half an inch wide, K, was unwound from the drum,
L, by the two rollers, M and N, which grip the paper between them as
they are turned by clockwork within the case, F.
[Illustration:
FIG. 286.—_Morse Recording Telegraph._
]
An important improvement was effected when, instead of steel points for
embossing the message, the Morse instrument was provided with an
arrangement for printing the signals in ink; since the pressure required
for embossing the paper is considerably greater than that needed merely
to bring it into contact with the edge of a little inked disc. In the
inking arrangement the strip of paper travels just below the margin of a
vertical disc, turned by the clockwork, and having its plane parallel to
the length of the paper strip. The narrow edge of this disc is kept
charged with printer’s ink, which it receives from a roller. The end of
the lever connected with the armature of the electro-magnet is formed of
a light strip of metal carrying a narrow projection at the end, over
which the paper passes, just beneath, but not touching, the inking disc.
When the current passes, the little projection is lifted up, and raises
the paper into contact with the ink, printing either a dot or a dash
according to the duration of the current. The amount of force required
to raise an inch or two of the length of the paper ribbon through a
space not greater than the twentieth of an inch is but small, and much
less than would be required to emboss the paper; so that in a great many
cases the part of the apparatus which is represented in Fig. 286, on the
right, may be dispensed with. In other cases it is, however, necessary;
as when, from the length of the line, the currents are too feeble to
give clear indications with the printing lever; and we shall, therefore,
presently describe its arrangement and purpose.
The clockwork is actuated by a spring, wound by the handle G, but its
action is suspended by a detent, which is released by touching the lever
H. When the clockwork is in action and the current constantly
circulating in the coils, a continuous line, parallel to the length of
the ribbon, would be printed upon it, in consequence of the contact with
the inking-disc, P, being maintained; but when a momentary current only
rushes through the coils, the armature attracted but for an instant,
gives rise to merely a dot on the passing paper, while a current of a
little duration will cause the paper to be marked with a short line or
dash.
The dot and the dash are the elementary signs of the Morse code of
signals, and these are producible according to the time the contact key
is held down at the distant station. By employing various combinations
of these two signs, the letters of the alphabet, numerals, &c., are
indicated. In selecting the combinations Professor Morse had regard to
the frequency with which the different letters recur in the English
language. Thus, for the letter E, which is more frequently used than any
other, the symbol chosen was a single dot; and for T, which is the next
most frequently employed, the dash was plainly the most appropriate;
then the four only possible combinations of the signs in pairs fell to
the next most frequent letters, and so on. The following table gives the
complete Morse code. The eye of the reader will doubtless detect a kind
of symmetry in the arrangement of the signs for the first five and last
five numerals:
ALPHABET.
┌──────────────────────────┬─────────┐
│ Letter. │ Sign. │
├──────────────────────────┼─────────┤
│ A │·- │
│ Ä │·-·- │
│ B │-··· │
│ C │-·-· │
│ D │-·· │
│ E │· │
│ É │··-·· │
│ F │··-· │
│ G │--· │
│ H │···· │
│ I │·· │
│ J │·--- │
│ K │-·- │
│ L │·-·· │
│ M │-- │
│ N │-· │
│ O │--- │
│ Ö │---· │
│ P │·--· │
│ Q │--·- │
│ R │·-· │
│ S │··· │
│ T │- │
│ U │··- │
│ Ü │··-- │
│ V │···- │
│ W │·-- │
│ X │-··- │
│ Y │-·-- │
│ Z │--·· │
│ Ch │---- │
└──────────────────────────┴─────────┘
NUMERALS.
┌──────────────────────────┬─────────┐
│ Numeral. │ Sign. │
├──────────────────────────┼─────────┤
│ 1 │·---- │
│ 2 │··--- │
│ 3 │···-- │
│ 4 │····- │
│ 5 │····· │
│ 6 │-···· │
│ 7 │--··· │
│ 8 │---·· │
│ 9 │----· │
│ 0 │----- │
└──────────────────────────┴─────────┘
PUNCTUATION, &c.
┌──────────────────────────┬─────────┐
│ │ Sign. │
├──────────────────────────┼─────────┤
│Full stop │······ │
│Colon │---··· │
│Semicolon │-·-·-· │
│Comma │·-·-·- │
│Interrogation │··--·· │
│Exclamation │--··-- │
│Hyphen │-····- │
│Apostrophe │·----· │
│[6]Fraction-line │------ │
│[7]Inverted commas │·-··-· │
│[7]Parenthesis │-·--·- │
│Italics or underlined │··--·- │
│New line │·-·-·· │
└──────────────────────────┴─────────┘
Footnote 6:
To be placed between the numerator and denominator of a vulgar
fraction.
Footnote 7:
To be placed before and after the words to which they refer.
OFFICIAL SIGNALS.
┌──────────────────────────┬─────────┐
│ │ Sign. │
├──────────────────────────┼─────────┤
│Public message │··· │
│Official Telegraph message│·- │
│Private message │·--· │
│Call │-·-·-·- │
│Correction, or rub out │···-· │
│Interruption │·········│
│Conclusion │·-·-·-· │
│Wait │·-··· │
│Receipt │·-··-··-·│
└──────────────────────────┴─────────┘
The length of a dot being taken as a unit, the length of a = 3 dots.
dash
The space between the signs composing a letter = 1 dot.
The space between two letters of a word = 3 dots.
The space between two following words = 6 dots.
[Illustration:
FIG. 287.—_Morse Transmitting Key._
]
[Illustration:
FIG. 288.—_Morse Transmitting Plate._
]
Fig. 287 is a view of the Morse transmitting key. A B is a brass lever,
moving in bearings at C, and provided at the end of its longer arm with
a large knob or button of some insulating material. Steel pins are
screwed in at B and D, and they are so adjusted that while that at B is
pressed against the projection, E, by the action of the spring, F, when
the knob, K, is pressed, contact is broken at B, and established at D. D
and E are each provided with a binding-screw, so that wires may be
attached in the manner indicated in Fig. 285. When the key is in the
position shown, a current arriving by the line-wire passes from the
fulcrum, C, of the lever through the contacts into the apparatus. When
the knob is pressed down the battery current enters the lever by the
contact at D, and passes into the line from the fulcrum, C. The clerks
who are called upon to transmit messages usually soon learn to time the
contacts very accurately in accordance with the code of signals, so as
to produce the dashes and lines with accuracy. However, with certain
persons some difficulty was found in acquiring the requisite uniformity,
and to obviate any objection on this score, Morse invented an
arrangement for facilitating the signalling, which is represented in
Fig. 288. This is a smooth tablet of a non-conducting substance, such as
ivory, except the shaded portions, which are plates of metal having
their surfaces even with that of the ivory, and all soldered to a plate
of metal beneath the ivory, which places them all in communication with
each other and with the binding-screw, C. The lengths of the strips of
metal and those of the spaces between them correspond with the dots and
dashes of the Morse alphabet as marked on the tablet. The battery wire
is connected with the binding-screw, C, and the line-wire terminates in
an elastic and flexible coil of insulated wire, which is attached to a
short rod having an insulated handle and terminated by a blunt platinum
point. This the transmitter takes in his hand and draws uniformly along
the line of metal strips belonging to the letter which he wishes to
telegraph. The circuit is closed while the point of the style is passing
across the metallic strips. This arrangement appears to be but little
used, but it is nevertheless admirable for its simplicity, and is
described here as a good illustration of the mode in which the varied
duration of the contacts is able to produce the signals of the Morse
alphabet. With the ordinary transmitting key a clerk is able to
telegraph, on the average, twenty or twenty-five words in a minute, but
the receiving apparatus is capable of recording three times as many.
Morse also invented a system of transmitting the messages automatically,
by setting up the message in a kind of type, just as ordinary letters
are arranged for printing. The type, if it may be so called, had simple
projections like the slips of metal, corresponding with each letter in
Fig. 288. The lines of the message were drawn under a contact-lever,
which closed the circuit when lifted up by the projections. Thus the
speed of transmission could be very greatly increased, and a single wire
and apparatus had its capacity of conveying a great number of messages
in a given time proportionately enlarged.
We have now to ask the reader’s attention to the details of the
apparatus in Fig. 286, the use of which has not already been pointed
out. The electro-magnet, O O´, and the parts immediately connected with
it, form what is called a _relay_. The object of this may be illustrated
by supposing that the instrument is at one end of a long line, such as
that between Edinburgh and London. Let us suppose it is at Edinburgh:
the currents sent from London by a battery of convenient size might not
be powerful enough to magnetize the soft iron of A with sufficient
intensity to give clearness to the signals. They are, therefore, made to
circulate in the electro-magnet, O, where they act by attracting the
armature, W, which has the form of a split tube of soft iron, attached
to a very light lever, Q, adjusted with great delicacy, and so that it
moves by little magnetic force. The end of the lever works between two
adjustable screws, R and S, which are electrically insulated, except
that R is in communication with one extremity of the coils of the
electro-magnet, A. Q is in metallic communication through the pillar, T,
and the binding-screw, U, with the zinc end of a battery at Edinburgh,
which is called the local battery, the other pole of which communicates
with the other ends of the coils, A, through the screw, U´. When no
current from London is passing through O, Q is held down by the spring,
W´, and the circuit of the local battery is broken; but the instant the
line-current passes, the armature, W, is attracted, and Q makes contact
with R, the current from the local battery rushes through the coils, A,
and the appropriate movements of the printing lever are effected by its
action. X is a spring for drawing down the lever, and it is provided
with a screw for adjusting its tension, and Y, Z, are screws for
limiting the extent of motion of the lever; under P is the little
projection by which the band of paper is pressed against the
inking-disc; _l_ and _e_ are respectively the screws for the line and
earth connections.
An extremely ingenious system of signalling, by which the speed could be
greatly increased, has been devised by Sir Charles Wheatstone, and is
largely adopted by the British postal authorities. In this system the
message is first translated into telegraphic language by a machine,
which punches certain holes in a strip of stiff paper. The apparatus
originally designed for this purpose by the inventor is thus described
by him in the Juror’s Report, International Exhibition of 1862:
“Long strips of paper are perforated by a machine constructed for the
purpose, with apertures grouped to represent the letters of the alphabet
and other signs. A strip thus prepared is placed in an instrument
associated with a source of electric power, which, on being set in
motion, moves it along, and causes it to act on two pins in such a
manner that when one of them is elevated the current is transmitted to
the telegraphic circuit in one direction, when the other is elevated it
is transmitted in the reverse direction. The elevations and depressions
of these pins are governed by the apertures and intervening intervals.
These currents, following each other indifferently in these two opposite
directions, act upon a writing instrument at a distant station in such a
manner as to produce corresponding marks on a slip of paper, moved by
appropriate mechanism.
“The first apparatus is a _perforator_, an instrument for piercing the
slips of paper with the apertures in the order required to form the
message. The slip of paper passes through a guiding groove, at the
bottom of which an opening is made sufficiently large to admit of the
to-and-fro motion of the upper end of a frame containing three punches,
the extremities of which are in the same transverse line. Each of these
punches, the middle one of which is smaller than the two external ones,
may be separately elevated by the pressure of a finger-key.
“By the pressure of either finger-key, simultaneously with the elevation
of its corresponding punch, in order to perforate the paper, two
different movements are successively produced: first, the raising of a
clip which holds the paper firmly in its position; and secondly, the
advancing motion of the frame containing the three punches, by which the
punch which is raised carries the slip of paper forward the proper
distance. During the reaction of the key consequent on the removal of
the pressure, the clip first fastens the paper, and then the frame falls
back to its normal position. The two external keys and punches are
employed to make the holes, which, grouped together, represent letters
and other characters, and the middle punch to make holes which mark the
intervals between the letters.
“The second apparatus is the _transmitter_, the object of which is to
receive the slips of paper prepared by the perforator, and to transmit
the currents in the order and direction corresponding to the holes
perforated in the slip. This it effects by mechanism somewhat similar to
that by which the perforator performs its functions. An eccentric
produces and regulates the occurrence of three distinct movements: 1.
The to-and-fro motion of a small frame which contains a groove fitted to
receive the slip of paper, and to carry it forward by its advancing
motion. 2. The elevation and depression of a spring-clip, which holds
the slip of paper firmly during the receding motion, but allows it to
move freely during the advancing motion. 3. The simultaneous elevation
of three wires placed parallel to each other, resting at one of their
ends over the axis of the eccentric, and their free ends entering
corresponding holes in the grooved frame. These three wires are not
fixed to the axis of the eccentric, but each end of them rests against
it by the upward pressure of a spring; so that when a light pressure is
exerted on the free end of either of them, it is capable of being
separately depressed. When the slip of paper is not inserted the
eccentric is in action; a pin attached to each of the external wires
touches during the advancing and receding motions of the frame a
different spring; and an arrangement is adopted, by means of insulation
and contacts properly applied, by which, while one of the wires is
elevated, the other remains depressed; the current passes to the
telegraphic circuit in one direction, and passes in the other direction
when the wire before elevated is depressed, and _vice versâ_; but while
both wires are simultaneously elevated or depressed the passing of the
current is interrupted. When the prepared slip of paper is inserted in
the groove, and moved forward whenever the end of one of the wires
enters an aperture in its corresponding row, the current passes in one
direction, and when the end of the other wire enters an aperture of the
other row, it passes in the other direction. By this means the currents
are made to succeed each other _automatically_ in their proper order and
direction to give the requisite variety of signals. The middle wire only
acts as a guide during the operation of the current.
“The wheel which drives the eccentric may be moved by the hand, or by
the application of any motive power. Where the movement of the
transmitter is effected by machinery, any number may be attended to by
one or two assistants. This transmitter requires only a single
telegraphic wire.
“The third apparatus is the _recording_ or _printing apparatus_, which
prints or impresses legible marks on a strip of paper, corresponding in
their arrangement with the apertures in the perforated paper. The pens
or styles are elevated or depressed by their connection with the moving
parts of the electro-magnets. The pens are entirely independent of each
other in their action, and are so arranged that when the current passes
through the coils of the electro-magnet in one direction, one of the
pens is depressed, and when it passes in the contrary direction the
other is depressed; when the currents cease, light springs restore the
pens to their elevated points. The mode of supplying the pens with ink
is the following: A reservoir about an eighth of an inch deep, and of
any convenient length and breath, is made in a piece of metal, the
interior of which may be gilt in order to avoid the corrosive action of
the ink; at the bottom of this reservoir are two holes, sufficiently
small to prevent by capillary attraction the ink from flowing through
them; the ends of the pens are placed immediately above these small
apertures, which they enter when the electro-magnets act upon them,
carrying with them a sufficient charge of ink to make a legible mark on
a ribbon of paper passing beneath them. The motion of the paper ribbon
is produced and regulated by apparatus similar to those employed in
other register and printing telegraphs.”
The mode by which Wheatstone proposed to indicate the letters was novel,
consisting in dots only, the numbers and positions of which in two lines
along the paper ribbon distinguished the letters—the system of combining
the symbols being still identical with the Morse code, only the dash was
replaced by a dot in the lower lines:
WHEATSTONE’S DOT SIGNALS.
˙⠄ ⠄˙˙˙ ⠄˙⠄˙ ⠄˙˙ ˙ ˙˙⠄˙ ⠄⠄˙ ˙˙˙˙ ˙˙ ˙⠄⠄⠄
A B C D E F G H I J
MORSE’S DOT AND DASH.
·- -··· -·-· -·· · ··-· -· ···· ·· ·-
A B C D E F G H I J
A single dot in the upper line stood for E, in the lower line for T; a
dot in the upper line, followed by one in the lower line a little to the
right, represented A; one in the lower line, followed by another in the
upper line, indicated N; and so on. By the dot printing it is said that
Wheatstone would signal 700 letters per minute. There were, however,
objections to the new code of signals: all the world had agreed to use
the Morse alphabet, and it was perhaps less liable to incorrect reading;
and for other reasons this more rapid signalling was unsuitable for
submarine lines. The apparatus has therefore been modified to suit the
dot and dash system of signals, and great improvements have been
effected by Sir Charles on the original instruments, with a view of
increasing the rapidity of transmission as much as possible. The paper
as punched for the Morse signals shows a row of equidistant holes in the
middle, by which the paper is guided uniformly forward, and in the outer
rows are holes arranged in pairs, either exactly opposite to each other
or obliquely—the former produce dots at the receiving station, the
latter dashes. From 60 to 100 words can thus be sent and printed in one
minute, and the automatic transmitting system can be applied to the
needle, or any other form of telegraph.
After a clerk has for some time been habituated to working with the
Morse instrument, he is able to read the message from the different
sounds made by the armature, as dashes or dots are respectively marked,
and he usually _listens_ to the message, and transcribes it at once into
ordinary language by the ear alone. This observation soon led to the
adoption of sound alone as the means of signalling, and an instrument on
this plan has already been referred to.