a bar of soft iron, the bar becomes magnetized while the current is
passing. If the bar be bent into the horse-shoe form, as in Fig. 6,
where A C B represents the bar, _a b c d e f_ the coil of insulated
wire, the bar acts as a magnet while the current is passing along the
coil, but ceases to do so as soon as the current is interrupted.[30]
If, then, we have a telegraphic wire from a distant station in electric
connection with the wire _a b c_, the part _e f_ descending to an
earth-plate, then, according as the operator at that distant station
transmits or stops the current, the iron A C B is magnetized or
demagnetized. The part C is commonly replaced by a flat piece of iron,
as is supposed to be the case with the temporary magnets shown in Fig.
7, where this flat piece is below the coils.
So far back as 1838 this property was applied by Morse in America
in the recording instrument which bears his name, and is now (with
slight modifications) in general use not only in America but on the
Continent. The principle of this instrument is exceedingly simple. Its
essential parts are shown in Fig. 7; H is the handle, H _b_ the lever
of the manipulator at the station A. The manipulator is shown in the
position for receiving a message from the station B along the wire W.
The handle H´ of the manipulator at the station B is shown depressed,
making connection at _a´_ with the wire from the battery N´ P´. Thus a
current passes through the handle to _c´_, along the wire to _c_ and
through _b_ to the coil of the temporary magnet M, after circling which
it passes to the earth at _e_ and so by E´ to the negative pole N´. The
passage of this current magnetizes M, which draws down the armature
_m_. Thus the lever _l_, pulled down on this side, presses upwards the
pointed style _s_ against a strip of paper _p_ which is steadily rolled
off from the wheel W so long as a message is being received. (The
mechanism for this purpose is not indicated in Fig. 7.) Thus, so long
as the operator at B holds down the handle H´, the style _s_ marks the
moving strip of paper, the spring _r_, under the lever _s l_, drawing
the style away so soon as the current ceases to flow and the magnet to
act. If he simply depresses the handle for an instant, a dot is marked;
if longer, a dash; and by various combinations of dots and dashes all
the letters, numerals, etc., are indicated. When the operator at B has
completed his message, the handle H´ being raised by the spring under
it (to the position in which H is shown), a message can be received at
B.
[Illustration: FIG. 7.]
I have in the figure and description assumed that the current from
either station acts directly on the magnet which works the recording
style. Usually, in long-distance telegraphy, the current is too weak
for this, and the magnet on which it acts is used only to complete the
circuit of a local battery, the current from which does the real work
of magnetizing M at A or M´ at B, as the case may be. A local battery
thus employed is called a _relay_.
The Morse instrument will serve to illustrate the _principle_ of the
methods by which facsimiles are obtained. The details of construction
are altogether different from those of the Morse instrument; they
also vary greatly in different instruments, and are too complex to be
conveniently described here. But the principle, which is the essential
point, can be readily understood.
In working the Morse instrument, the operator at B depresses the handle
H´. Suppose that this handle is kept depressed by a spring, and that
a long strip of paper passing uniformly between the two points at _a_
prevents contact. Then no current can pass. But if there is a hole in
this paper, then when the hole reaches _a_ the two metal points at _a_
meet and the current passes. We have here the principle of the Bain
telegraph. A long strip of paper is punched with round and long holes,
corresponding to the dots and marks of a message by the Morse alphabet.
As it passes between a metal wheel and a spring, both forming part of
the circuit, it breaks the circuit until a hole allows the spring to
touch the wheel, either for a short or longer time-interval, during
which the current passes to the other station, where it sets a relay
at work. In Bain’s system the message is received on a chemically
prepared strip of paper, moving uniformly at the receiving station, and
connected with the negative pole of the relay battery. When contact is
made, the face of the paper is touched by a steel pointer connected
with the positive pole, and the current which passes from the end of
the pointer through the paper to the negative pole produces a blue
mark on the chemically prepared paper.[31]
We see that by Bain’s arrangement a paper is marked with dots and
lines, corresponding to round and elongated holes, in a ribbon of
paper. It is only a step from this to the production of facsimiles of
writings or drawings.
Suppose a sheet of paper so prepared as to be a conductor of
electricity, and that a message is written on the paper with some
non-conducting substance for ink. If that sheet were passed between
the knobs at _a_ (the handle H being pressed down by a spring),
whilst simultaneously a sheet of Bain’s chemically prepared paper
were passed athwart the steel pointer at the receiving station,
there would be traced across the last-named paper a blue line, which
would be broken at parts corresponding to those on the other paper
where the non-conducting ink interrupted the current. Suppose the
process repeated, each paper being slightly shifted so that the line
traced across either would be parallel and very close to the former,
but precisely corresponding as respects the position of its length.
Then this line, also, on the recording paper will be broken at parts
corresponding to those in which the line across the transmitting paper
meets the writing. If line after line be drawn in this way till the
entire breadth of the transmitting paper has been crossed by close
parallel lines, the entire breadth of the receiving paper will be
covered by closely marked blue lines except where the writing has
broken the contact. Thus a negative facsimile of the writing will
be found in the manner indicated in Figs. 8 and 9.[32] In reality,
in processes of this kind, the papers (unlike the ribbons on Bain’s
telegraph) are not carried across in the way I have imagined, but are
swept by successive strokes of a movable pointer, along which the
current flows; but the principle is the same.
[Illustration: FIG. 8. FIG. 9.]
It is essential, in such a process as I have described, first, that the
recording sheet should be carried athwart the pointer which conveys
the marking current (or the pointer carried across the recording
sheet) in precise accordance with the motion of the transmitting sheet
athwart the wire or style which conveys the current to the long wire
between the stations (or of this style across the transmitting sheet).
The recording sheet and the transmitting sheet must also be shifted
between each stroke by an equal amount. The latter point, is easily
secured; the former is secured by causing the mechanism which gives the
transmitting style its successive strokes to make and break circuit,
by which a temporary magnet at the receiving station is magnetized and
demagnetized; by the action of this magnet the recording pointer is
caused to start on its motion athwart the receiving sheet, and moving
uniformly it completes its thwart stroke at the same instant as the
transmitting style.
Caselli’s pantelegraph admirably effects the transmission of
facsimiles. The transmitting style is carried by the motion of a
heavy pendulum in an arc of constant range over a cylindrical surface
on which the paper containing the message, writing, or picture, is
spread. As the swing of the pendulum begins, a similar pendulum at the
receiving station begins its swing; the same break of circuit which
(by demagnetizing a temporary magnet) releases one, releases the other
also. The latter swings in an arc of precisely the same range, and
carries a precisely similar style over a similar cylindrical surface
on which is placed the prepared receiving paper. In fact, the same
pendulum at either station is used for transmitting and for receiving
facsimiles. Nay, not only so, but each pendulum, as it swings, serves
in the work both of transmitting and recording facsimiles. As it
swings one way, it travels along a line over each of two messages or
drawings, while the other pendulum in its synchronous swing traces a
corresponding line over each of two receiving sheets; and as it swings
the other way, it traces a line on each of two receiving sheets,
corresponding to the lines along which the transmitting style of the
other is passing along two messages or drawings. Such, at least, is the
way in which the instrument works in busy times. It can, of course,
send a message, or two messages, without receiving any.[33]
In Caselli’s pantelegraph matters are so arranged that instead of a
negative facsimile, like Fig. 9, a true facsimile is obtained in all
respects except that the letters and figures are made by closely set
dark lines instead of being dark throughout as in the message. The
transmitting paper is conducting and the ink non-conducting, as in
Bakewell’s original arrangement; but instead of the conducting paper
completing the circuit for the distant station, it completes a short
home circuit (so to speak) along which the current travels without
entering on the distant circuit When the non-conducting ink breaks the
short circuit, the current travels in the long circuit through the
recording pointer at the receiving station; and a mark is thus made
corresponding to the inked part of the transmitting sheet instead of
the blank part, as in the older plan.
The following passage from Guillemin’s “Application of the Physical
Forces” indicates the effectiveness of Caselli’s pantelegraph not
only as respects the character of the message it conveys, but as
to rapidity of transmission. (I alter the measures from the metric
to our usual system of notation.[34]) “Nothing is simpler than the
writing of the pantelegraph. The message when written is placed on
the surface of the transmitting cylinder. The clerk makes the warning
signals, and then sets the pendulum going. The transmission of the
message is accomplished automatically, without the clerk having any
work to do, and consequently without [his] being obliged to acquire
any special knowledge. Since two despatches may be sent at the same
time—and since shorthand may be used—the rapidity of transmission
may be considerable.” “The long pendulum of Caselli’s telegraph,” says
M. Quet, “generally performs about forty oscillations a minute, and
the styles trace forty broken lines, separated from each other by less
than the hundredth part of an inch. In one minute the lines described
by the style have ranged over a breadth of more than half an inch,
and in twenty minutes of nearly 10½ inches. As we can give the lines
a length of 4¼ inches, it follows that in twenty minutes Caselli’s
apparatus furnishes the facsimile of the writing or drawing traced on a
metallized plate 4¼ inches broad by 10½ inches long. For clearness of
reproduction, the original writing must be very legible and in large
characters.” “Since 1865 the line from Paris to Lyons and Marseilles
has been open to the public for the transmission of messages by this
truly marvellous system.”
It will easily be seen that Caselli’s method is capable of many
important uses besides the transmission of facsimiles of handwriting.
For instance, by means of it a portrait of some person who is to be
identified—whether fraudulent absconder, or escaped prisoner or
lunatic, or wife who has eloped from her husband, or husband who has
deserted his wife, or missing child, and so on—can be sent in a few
minutes to a distant city where the missing person is likely to be. All
that is necessary is that from a photograph or other portrait an artist
employed for the purpose at the transmitting station should, in bold
and heavy lines, sketch the lineaments of the missing person on one
of the prepared sheets, as in Fig. 10. The portrait at the receiving
station will appear as in Fig. 11, and if necessary an artist at this
station can darken the lines or in other ways improve the picture
without altering the likeness.
[Illustration: FIG. 10. FIG. 11.]
But now we must turn to the greatest marvel of all—the transmission of
tones, tunes, and words by the electric wire.
The transmission of the rhythm of an air is of course a very simple
matter. I have seen the following passage from “Lardner’s Museum of
Science and Art,” 1859, quoted as describing an anticipation of the
telephone, though in reality it only shows what every one who has
heard a telegraphic indicator at work must have noticed, that the
click of the instrument may be made to keep time with an air. “We
were in the Hanover Street Office, when there was a pause in the
business operations. Mr. M. Porter, of the office at Boston—the
writer being at New York—asked what tune we would have? We replied,
‘Yankee Doodle,’ and to our surprise he immediately complied with our
request. The instrument, a Morse one, commenced drumming the notes of
the tune as perfectly and distinctly as a skilful drummer could have
made them at the head of a regiment, and many will be astonished to
hear that ‘Yankee Doodle’ can travel by lightning.... So perfectly
and distinctly were the sounds of the tunes transmitted, that good
instrumental performers could have no difficulty in keeping time with
the instruments at this end of the wires.... That a pianist in London
should execute a fantasia at Paris, Brussels, Berlin, and Vienna, at
the same moment, and with the same spirit, expression, and precision as
if the instruments at these distant places were under his fingers, is
not only within the limits of practicability, but really presents no
other difficulty than may arise from the expense of the performances.
From what has just been stated, it is clear that the time of music
has been already transmitted, and the production of the sounds does
not offer any more difficulty than the printing of the letters of a
despatch.” Unfortunately, Lardner omitted to describe how this easy
task was to be achieved.
Reuss first in 1861 showed how a sound can be transmitted. At the
sending station, according to his method, there is a box, into which,
through a pipe in the side, the note to be transmitted is sounded. The
box is open at the top, and across it, near the top, is stretched
a membrane which vibrates synchronously with the aerial vibrations
corresponding to the note. At the middle of the membrane, on its upper
surface, is a small disc of metal, connected by a thin strip of copper
with the positive pole of the battery at the transmitting station. The
disc also, when the machine is about to be put in use, lightly touches
a point on a metallic arm, along which (while this contact continues)
the electric current passes to the wire communicating with the distant
station. At that station the wire is carried in a coil round a straight
rod of soft iron suspended horizontally in such a way as to be free
to vibrate between two sounding-boards. After forming this coil, the
wire which conveys the current passes to the earth-plate and so home.
As already explained, while the current passes, the rod of iron is
magnetized, but the rod loses its magnetization when the current ceases.
Now, when a note is sounded in the box at the transmitting station, the
membrane vibrates, and at each vibration the metal disc is separated
from the point which it lightly touches when at rest. Thus contact is
broken at regular intervals, corresponding to the rate of vibration
due to the note. Suppose, for instance, the note _C_ is sounded; then
there are 256 complete vibrations in a second, the electric current is
therefore interrupted and renewed, and the bar of soft iron magnetized
and demagnetized, 256 times in a second. Now, it had been discovered
by Page and Henry that when a bar of iron is rapidly magnetized
and demagnetized, it is put into vibrations synchronizing with the
interruptions of the current, and therefore emits a note of the same
tone as that which has been sounded into the transmitting box.
Professor Heisler, in his “Lehrbuch der technischen Physik,” 1866,
wrote of Reuss’s telephone: “The instrument is still in its infancy;
however, by the use of batteries of proper strength, it already
transmits not only single musical tones, but even the most intricate
melodies, sung at one end of the line, to the other, situated at a
great distance, and makes them perceptible there with all desirable
distinctness.” Dr. Van der Weyde, of New York, states that, after
reading an account of Reuss’s telephone, he had two such instruments
constructed, and exhibited them at the meeting of the Polytechnic
Club of the American Institute. “The original sounds were produced at
the furthest extremity of the large building (the Cooper Institute),
totally out of hearing of the Association; and the receiving
instrument, standing on the table in the lecture-room, produced, with
a peculiar and rather nasal twang, the different tunes sung into the
box at the other end of the line; not powerfully, it is true, but very
distinctly and correctly. In the succeeding summer I improved the form
of the box, so as to produce a more powerful vibration of the membrane.
I also improved the receiving instrument by introducing several iron
wires into the coil, so as to produce a stronger vibration. I submitted
these, with some other improvements, to the meeting of the American
Association for the Advancement of Science, and on that occasion (now
seven years ago) expressed the opinion that the instrument contained
the germ of a new method of working the electric telegraph, and would
undoubtedly lead to further improvements in this branch of science.”
The telephonic successes recently achieved by Mr. Gray were in
part anticipated by La Cour, of Copenhagen, whose method may be
thus described: At the transmitting station a tuning-fork is set
in vibration. At each vibration one of the prongs touches a fine
strip of metal completing a circuit. At the receiving station the
wire conveying the electric current is coiled round the prongs of
another tuning-fork of the same tone, but without touching them.
The intermittent current, corresponding as it does with the rate of
vibration proper to the receiving fork, sets this fork in vibration;
and in La Cour’s instrument the vibrations of the receiving fork
were used to complete the circuit of a local battery. His object was
not so much the production of tones as the use of the vibrations
corresponding to different tones, to act on different receiving
instruments. For only a fork corresponding to the sending fork could
be set in vibration by the intermittent current resulting from the
latter’s vibrations. So that, if there were several transmitting forks,
each could send its own message at the same time, each receiving fork
responding only to the vibrations of the corresponding transmitting
fork. La Cour proposed, in fact, that his instrument should be used
in combination with other methods of telegraphic communication. Thus,
since the transmitting fork, whenever put in vibration, sets the local
battery of the receiving station at work, it can be used to work a
Morse instrument, or it could work an ordinary Wheatstone and Cook
instrument, or it could be used for a pantelegraph. The same wire, when
different forks are used, could work simultaneously several instruments
at the receiving station. One special use indicated by La Cour was the
adaptation of his system to the Caselli pantelegraph, whereby, instead
of one style, a comb of styles might be carried over the transmitting
and recording plates. It would be necessary, in all such applications
of his method (though, strangely enough, La Cour’s description makes
no mention of the point), that the vibrations of the transmitting fork
should admit of being instantly stopped or “damped.”
Mr. Gray’s system is more directly telephonic, as aiming rather at the
development of sound itself than at the transmission of messages by
the vibrations corresponding to sound. A series of tuning-forks are
used, which are set in separate vibration by fingering the notes of a
key-board. The vibrations are transmitted to a receiving instrument
consisting of a series of reeds, corresponding in note to the series of
transmitting forks, each reed being enclosed in a sounding-box. These
boxes vary in length from two feet to six inches, and are connected
by two wooden bars, one of which carries an electro-magnet, round the
coils of which pass the currents from the transmitting instrument. When
a tuning-fork is set in vibration by the performer at the transmitting
key-board, the electro-magnet is magnetized and demagnetized
synchronously with the vibrations of the fork. Not only are vibrations
thus imparted to the reed of corresponding note, but these are
synchronously strengthened by thuds resulting from the lengthening of
the iron when magnetized.
So far as its musical capabilities are concerned, Gray’s telephone can
hardly be regarded as fulfilling all the hopes that have been expressed
concerning telephonic music. “Dreaming enthusiasts of a prophetic turn
of mind foretold,” we learn, “that a time would come when future Pattis
would sing on a London stage to audiences in New York, Berlin, St.
Petersburg, Shanghai, San Francisco, and Constantinople all at once.”
But the account of the first concert given at a distance scarcely
realizes these fond expectations. When “Home, Sweet Home,” played at
Philadelphia, came floating through the air at the Steinway Hall, New
York, “the sound was like that of a distant organ, rather faint, for a
hard storm was in progress, and there was consequently a great leakage
of the electric current, but quite clear and musical. The lower notes
were the best, the higher being sometimes almost inaudible. ‘The Last
Rose of Summer,’ ‘Com’ è gentil,’ and other melodies, followed, with
more or less success. There was no attempt to play chords,” though
three or four notes can be sounded together. It must be confessed that
the rosy predictions of M. Strakosch (the _impresario_) “as to the
future of this instrument seem rather exalted, and we are not likely as
yet to lay on our music from a central reservoir as we lay on gas and
water, though the experiment was certainly a very curious one.”
The importance of Mr. Gray’s, as of La Cour’s inventions, depends,
however, far more on the way in which they increase the message-bearing
capacity of telegraphy than on their power of conveying airs to a
distance. At the Philadelphia Exhibition, Sir W. Thomson heard four
messages sounded simultaneously by the Gray telephone. The Morse
alphabet was used. I have mentioned that in that alphabet various
combinations of dots and dashes are used to represent different
letters; it is only necessary to substitute the short and long duration
of a note for dots and dashes to have a similar sound alphabet.
Suppose, now, four tuning-forks at the transmitting station, whose
notes are _Do_ [Illustration], _Mi_, _Sol_, and _Do_ [Illustration],
or say _C_, _E_, _G_, and _C_´, then by each of these forks a
separate message may be transmitted, all the messages being carried
simultaneously by the same line to separate sounding reeds (or forks,
if preferred), and received by different clerks. With a suitable
key-board, a single clerk could send the four messages simultaneously,
striking chords instead of single notes, though considerable practice
would be necessary to transform four verbal messages at once into the
proper telephonic music, and some skill in fingering to give the proper
duration to each note.
Lastly, we come to the greatest achievement of all, Professor Graham
Bell’s vocal telephone. In the autumn of 1875 I had the pleasure
of hearing from Professor Bell in the course of a ride—all too
short—from Boston to Salem, Mass., an account of his instrument as
then devised, and of his hopes as to future developments. These hopes
have since been in great part fulfilled, but I venture to predict that
we do not yet know all, or nearly all, that the vocal telephone, in
Bell’s hands, is to achieve.
It ought to be mentioned at the outset that Bell claims to have
demonstrated in 1873 (a year before La Cour) the possibility of
transmitting several messages simultaneously by means of the Morse
alphabet.