ACOUSTICS (_Continued_).
THE TOPOPHONE—THE MEGAPHONE—THE AUTOPHONE—THE AUDIPHONE—THE
TELEPHONE—THE PHONOGRAPH—THE MICROPHONE.
We propose in this chapter to give as shortly as possible a description
of the various instruments lately come into use, by means of which,
and electricity, sounds can be carried from place to place, and their
locality identified. It is only within the last few years that these
wonderful inventions have come into use, and in a measure superseded
the at one time invincible electric telegraph. The Telephone is now
in daily use in London and other places, and its novelty, if not
all its capability, has been discounted. The Phonograph has also
been frequently seen. So we will on this occasion commence with the
TOPOPHONE, a rather novel instrument.
As the name indicates, the TOPOPHONE is an apparatus for
discovering the position of a sound, from the Greek words signifying
a “place” and “sound.” The _sources_ of sound can be found by it, and
indeed this is its actual and practical use. It is claimed for this
new apparatus that it stands in the same relation to the sailor as his
old and trusty friends, the compass and sextant. These in navigation
inform the steersman as to his course, and tells him his position by
observation. The Topophone will tell him whence a sound arises, its
origin wherever it may be; and this in a fog is no mean advantage.
Suppose a ship to be approaching a dangerous coast in a fog. We are all
aware how deceptive sounds are when heard through such a medium. We
cannot tell from what precise direction the horn, whistle, or bell is
sounding. The Topophone will give us the exact spot, and we can then,
from our general knowledge of the locality, work our vessel up the
river, or into the harbour, in safety.
The Topophone was invented in 1880, by Professor Alfred Mayer, an
American, and is based upon the well-known theory of sound waves.
These, as we have already explained, exist in the air; and if the
theory of sound waves has perfected the Topophone, we can fairly say
that it has confirmed the supposed form of the sound waves. “Sound,”
says the inventor of the apparatus, “is supposed to be a particle
continually expanding in the air, composed of a wave produced by
compression, and followed by rarefaction. A continuous sound is a
series of these particles or globules spreading and expanding as the
water-rings in a pond.” This much will be at once perceived.
Now, suppose a person up to his shoulders in a pond of water, and
someone throws a stone into it. If that person extend his arms and
hands at right angles facing the sound, each hand would touch the edge
of a ripple as it came towards him across the pond. He would then be
facing the source of the ripples or waves, and look along a radius
of the circle formed by the waves. But if he please, he can move his
body so that both hands shall touch the same wave at the same time,
or he might turn away from the source, and only one hand would touch
the wave. But when both hands are actually washed by the same circular
ripple he must be facing the source of it. Any position in which his
fingers did not touch the ripple almost at the same instant, would not
be facing the source of the wave ripples. So by turning and extending
his hands, he could with his eyes shut find out whether he was or was
not facing the original source of the waves.
This applied to sound waves in the air is the whole theory of the
Topophone, which, however, depends for its usefulness upon the same
note being sounded by all horns and whistles. One note must be better
than all the others, and that note, probably C (treble), caused by
about two hundred and sixty vibrations per second, has been found most
applicable. If all whistles and horns can by law be compelled to adjust
themselves to this note, then the Topophone will be a real and lasting
benefit.
Let us now look at the apparatus itself.
It being conceded that the resonators are in the same key as the
Foghorn,—and this is necessary,—they are placed upon the deck of the
vessel. An ear-tube of indiarubber is carried from each of these
“resonators” into the cabin. These tubes unite and again separate,
ending in small pieces ready to be fitted to the ears. The apparatus
is fixed on deck, and the arrangement which supports it passes into
the cabin, and can be turned about in any direction. Of course in this
case a dial point is necessary to indicate the direction in which the
instrument is turned. If the machine be worn on the shoulders of the
officer of the watch he can move as he pleases, and wants no indicator.
The Topophone when used is so constructed, that when a horn is heard,
and when the listener is facing the sound, he can _hear nothing_! When
not facing the origin of the sound he can hear the horn very well, but
the moment the resonators receive the sound together as they face the
source, a very low murmur is heard, or perhaps no sound at all.—Why?
A certain pitch of tone is composed of vibrations or waves of equal
length. In all waves there is a hollow and a crest. One neutralizes
the other. The hollow of a sound wave meeting the crest of another
wave “interferes” to produce silence, stillness, a dead level. So in
“light”; two rays will produce darkness. We will endeavour to explain
this.
If we have two equal strings, each performing an equal number of
vibrations in a second, they will produce equal sound waves, and the
sound produced by both together will be uninterrupted, and twice as
loud as one of them. But if one string vibrate, say one hundred times,
and the other one hundred and one times in a second, they will _not_
be in unison, and one will gain upon the other string, till after it
has got to fifty vibrations it will be half a vibration ahead. At that
moment they will neutralize each other, and silence will ensue for an
appreciable time.
[Illustration: Fig. 185.—The Megaphone.]
In the case of light suppose a _red_ ray strikes the eye, and another
red ray to come upon it from somewhere else. If the difference between
its distance and the other point from the spot in the retina on which
the first ray fell, is the 258/1000 part of an inch, or exactly twice,
thrice, four times as much, etc., that distance, the light will be seen
twice as strong. But if the difference in the distances between the
points whence the light comes be only _one-half the 258/1000 part of an
inch_, or 1½, 2½, 3½, or 4½ times that distance, one light
will extinguish the other, and darkness will be the result. Now this
is precisely what happens in the case of the Topophone. To return to
our simile of water waves. If two stones be cast into a pond, and two
equal and similar waves produced, and if they reach a certain place at
the same moment, they will make one large wave. But if one followed
the other a little, so that the hollow of one coincided with the crest
of the other, and _vice versâ_, the waves would obliterate each other,
and a dead level would result. One tube of the Topophone is half a wave
length longer than the other, and when the resonators are in a line and
receive the wave at the same time, one ear hears the elevation of the
sound wave, and the other the depression,—the sound is neutralized, and
comparative, if not actual, silence results. The sailor knows in what
direction the land lies, and can calculate his distance, or anchor if
he please.
If amongst our readers there be any who wish to make for themselves an
acoustic signalling apparatus there is physically nothing to prevent
them from constructing such an instrument as that shown in the annexed
woodcut (fig. 185). It is founded upon the speaking-trumpet principle,
which is supposed to have been originated by Samuel Markland, in 1670.
Kircher, in his “_Ars magna et umbra_,” and in his “_Phonurgia_,”
mentions a kind of speaking-trumpet, or _porte voix_, of gigantic
dimensions, and called the “Horn of Alexander.” According to Kircher,
the instrument was used by Alexander the Great to summon his soldiers
from a distance of ten miles. The diameter of the circumference was
about eight feet, and Kircher conjectured that the instrument was
mounted upon three supports.
During the last century, a German professor, named Huth, made a model
of the horn, and found it answered every purpose of a speaking-trumpet
with most powerful results, but we beg leave to doubt whether the
instrument really carried the voice to any very great distance.
The Acoustic Cornet, which is the counterpart of the speaking-trumpet,
has been made in many different forms during the last two centuries,
but none of them to the present time consist of anything more intricate
than a simple tube with a mouthpiece and bell-shaped orifice.
Professor Edison, however, in his researches regarding the conveyance
of sounds, has made numerous and interesting experiments. On one
occasion, with his Megaphone he carried on a conversation at a distance
of nearly two miles, without any other assistance from instruments
except a few little cornets of cardboard. These constitute the
Megaphone, which may be regarded as a curiosity, considering the
effects produced by such simple means. The illustration (fig. 185)
represents the instrument which is (or was lately) fixed upon the
balcony of Mr. Edison’s house. At a mile-and-a-half distant from the
house, at a spot indicated by the two birds in the picture, another
instrument was fixed, and conversation was carried on with ease.
Perhaps the present opportunity will be the most convenient to speak of
the AUTOPHONE, although it is more a musical than an acoustic
instrument. Until lately Barbary organs and piano organs have been the
only means by which poor people have been able to hear any music, and
that not of a very elevated class. Besides, there is a good deal of
expense connected with the possession of an organ. But the Americans,
with a view to popularize music, have invented the AUTOPHONE,
which is simply a mechanical accordeon, manufactured by the Autophone
Company, of Ithaca, New York.
The principle of the instrument is represented in fig. 186, and is
extremely simple. An upright frame carries within it on one side a
bellows, and on the other a flexible air chamber, which serves as a
reservoir.
The upper portion contains a set of stops like an accordeon, but the
escape of the air through the small vibrating plates can only take
place by the upper surface of the frame work, upon which slides a thin
plate of Bristol board pierced with holes at convenient distances, and
set in motion by the mechanism shown in the annexed diagram (fig. 187).
[Illustration: Fig. 186.—The Autophone.]
The figure represents an axle furnished with a series of “washers,”
which, acting upon the plate, cause it to move round. It is the bellows
movement that turns the axle by the aid of two “catches,” B
and C, which work upon a toothed wheel fixed upon it.
The “catch” B moves the paper on which the tune is
“perforated,” when the bellows is empty, the other catch when it is
distended; but a counter catch, D, represented by the dotted
lines in the illustration, is so arranged that the paper cannot pass
on except the tooth of the catch D is opposite a hole pierced
upon the plate above. In the contrary case there is no movement of
the paper during the dilatation of the bellows. The effect of this
very ingenious arrangement is to give to the “musical” band of “board”
an irregular movement, but it economises it in the case of sustained
notes. The whole action of the instrument depends upon the correct
working of the bellows.
The effect, from an artistic point of view, certainly leaves something
to be desired, but the instrument is cheap, and not cumbersome, and
the slips of paper upon which the music is “cut out” can be made by
machinery, and consequently are not dear. So far, the Autophone is
fitted for popular favour and use, and may supersede the barrel organ.
[Illustration: Fig. 187.—Detail of the Autophone.]
The AUDIPHONE is an instrument to conduct sound to the ear,
to supplement it when temporary or partial deafness has occurred. Very
likely many of our readers have observed ladies carrying large black
fans on occasions,—at church, or lecture, or theatre,—and wondered
why, perhaps. Those “fans” are Audiphones. The instrument is made of
vulcanized rubber, and consists of a long flexible disc supported by
a handle. To the upper edge of the “fan” are attached cords, which
pass through a clip on the handle. If the person who wishes to hear by
means of the Audiphone will hold the fan against the upper teeth,—the
convex side of the fan outward,—he or she will hear distinctly, for
the vibrations of sound are collected and strike upon the teeth and
bones, and act upon the auditory nerves from within, precisely as the
vibrations act from without through the auricle. We need hardly add
that if the ear be injured the Audiphone will be of no use. A writer
says: “From personal observation with the Audiphone it appears to
convey the sonorous vibrations to the ear through the teeth, just as
a long wooden rod held in the teeth will convey the vibrations of the
sounding-board of a piano, though the piano is in another room and out
of hearing by the ear. In using the Audiphone during conversation there
is no movement or vibration felt by the teeth; in listening to a piano
there is a very faint sensation as if the Audiphone vibrated slightly,
while with the handle of the Audiphone resting on the sounding-board
of the piano the vibrations are so violent as to be painful to the
teeth. By closing the ears a person with even acute hearing can observe
the admirable manner in which the instrument conveys spoken words to
the ear. The Audiphone will prove to be of great value to deaf mutes,
as it enables them to hear their own voices, and thus to train them
to express words, while, before, they could only make inarticulate
sounds.”
We have a variation of this instrument which has been introduced
employing a diaphragm held in a telephone mouthpiece, and free to
vibrate under the influence of sounds. This is connected by a string
to a bit of wood that may be held in the teeth. In use the hearer
places the wood between his teeth, the string is drawn tight, and the
speaker speaks through the telephone mouthpiece, the vibrations of
the diaphragm being then conveyed to the teeth through the stretched
string. This apparatus works very successfully, and ladies use it, but
it is not so convenient for general use as the Audiphone.
[Illustration: Fig. 188.—The Telephone.]
The Telephone is now in daily use in London, and is by no means
strange to the majority of our countrymen, still some description of
it will probably be acceptable, and a glance at its history may prove
interesting.
[Illustration: Fig. 189.—The “receiving” apparatus.]
In speaking of the Telephone, we must not lose sight of the facts
before mentioned, as regards our sense of hearing, and the manner in
which the ear acts by the series of bones termed the hammer, the anvil,
and stirrup. In the process of reproduction of tone in the magnetic
instruments, the mechanism of the human ear was, to a certain extent,
imitated, and a diaphragm, by vibrations, generates and controls an
electric current.
Professor Wheatstone was the first person to employ the electric
wire for the transmission of sounds, but Professor Philip Reiss, of
Friedrichsdorf, was the first to make the experiment of producing
musical sounds at a distance. His first instrument was of a most
primitive nature; subsequently he produced an instrument of which fig.
188 is the Telephone, fig. 189 the “receiver.”
In fig. 188, it will be seen that there is an aperture on the top and
one at the side; the latter is the mouthpiece. The top aperture is
covered with a membrane which is stretched very tightly. When a person
speaks or sings into the mouthpiece his voice is at once concentrated
upon the tight membrane, which it causes to vibrate in a manner
corresponding with the vibrations of the voice. There are two binding
screws, one at each side. To the centre of the tight membrane a piece
of platinum is fixed, and this is connected with the binding screw on
one side, in which a wire from the battery is fixed. On the membrane
is a tripod, the feet of which (two) rest in metal cups, one of them
being in a mercury cup connected with the binding screw at the opposite
side to that already mentioned. The third “foot”—a platinum point—is on
the platinum in the centre of the membrane or top, and moves with it.
Every time the membrane is stretched by a vibration the platinum point
is touched, and the closed circuit is broken by the return of each
vibration.
[Illustration: Fig. 190.—Bell’s first Telephone (Transmitter).
_a._ Electro-magnet. _b._ Diaphragm. _c._ Collar. _d._ Collar and tube.
_f._ Screw. _g._ Mouthpiece. _h._ Battery. _i._ Wire from battery to
coil. _k._ Telegraph wire. _l._ Through binding screw. _m._ Pillar
holding magnet.]
The receiving instrument (fig. 189) consists of a coil enclosing an
iron rod, and fixed upon a hollow sounding box. It is founded upon a
fact discovered by Professor Henry, that iron bars when magnetized by
an electric current become a little longer, and at the interruption
of the current resume their former length. Thus in the receiver the
iron will become alternately longer and shorter in accordance with the
vibrations of the membrane in the box far away, and so the longitudinal
vibrations of the bar of iron will be communicated to the sounding box,
and become perfectly audible. This instrument, however, could only
produce the “pitch” of sound, “not different degrees of intensity, or
other qualities of tones.” It merely sang with its own little trumpet
whatever was sung into it; for all the waves were produced by an
electric current of a certain and uniform strength, and therefore the
sound waves were of the same size.
But in 1874, Mr. Elisha Gray, of Chicago, improved Reiss’ instrument,
and discovered a method by which the intensity or loudness of tones, as
well as their “pitch,” were transmitted and reproduced. In this method
he employed electrical vibrations of varying strength and rapidity,
and so was enabled to reproduce a tune. Subsequently he conceived the
notion of controlling the vibrations by means of a diaphragm, which
responded to every known sound, and by this he managed to transmit
speech in an articulate manner.
[Illustration: Fig. 191.—Bell’s Telephone (Receiver).]
In 1876, Professor Graham Bell sent a Telephone to the Centennial
Exhibition at Philadelphia. Mr. Bell, according to the report, managed
to produce a variation of strength of current in exact proportion to
the particle of air moved by the sound. A piece of iron attached to
a membrane, and moved to and fro in proximity to an electro magnet,
proved successful. The battery and wire of the electro magnet are in
circuit with the telegraph wire, and the wire of another electro magnet
at the receiving station. This second magnet has a solid bar of iron
for core, which is connected at one end, by a thick disc of iron, to
an iron tube surrounding the coil and bar. The free circular end of
the tube constitutes one pole of the electro magnet, and the adjacent
free end of the bar core the other. A thin circular iron disc held
pressed against the end of the tube by the electro-magnetic attraction,
and free to vibrate through a very small space without touching the
central pole, constitutes the sounder by which the electric effect is
reconverted into sound. The accompanying illustrations (figs. 190, 191)
show Mr. Bell’s Telephone as described.
The Telephone, subsequently simplified by Professor Bell, is shown in
the two following illustrations (figs. 192, 193). The voice strikes
against the diaphragm, and it begins to vibrate. The _sound_ is not
conveyed by the wire; the _motion_ is communicated, and the vibrations
become sound waves again. The Telephone consists of a cylindrical
magnet encircled at one end by a bobbin, on which is wound a quantity
of fine insulated copper wire. The magnet and coil are contained in a
wooden case, the ends of the coil being soldered to thick copper wire,
which traverse the “wooden envelope,” and terminate in the binding
screws. In front of the magnet is a thin circular iron plate, in which
is the mouthpiece. The drawings will explain the instrument.
[Illustration: Fig. 192.—External appearance of Bell Telephone.]
[Illustration: Fig. 193.—_a._ Bobbin of coil wire round magnet. _b._
Diaphragm. _c._ Mouthpiece. _d._ Permanent magnet. _e._ Wires to
binding screws. _f._ Both wires as one for convenience. _g._ Adjusting
screw-holding magnet.]
Mr. Edison also invented a Telephone like Gray’s, and made the
discovery, that when properly prepared, carbon would change its
resistance with pressure, and that the ratio of these changes
corresponded with the pressure. This solved the problem of the
production of speech. The carbon is placed between two plates of
platinum connected in the circuit and near the diaphragm, and the
carbon receives the pressure from it by means of the mouthpiece.
When we come to MAGNETISM and ELECTRICITY we may have
something more to say respecting the mysteries of the Telephone and
its later developments. At present we are only concerned with it as a
sound conveyer, and it answers its purpose admirably, although somewhat
liable to attract other sounds or vibrations from neighbouring wires.
The PHONOGRAPH, a mechanical invention of Mr. Edison, does not
make use of electricity, although the vibratory motion of the diaphragm
is utilized. It, in a simple form, consists of a diaphragm so arranged
as to operate upon a small stylus, placed just opposite and below the
centre, and a brass cylinder, six or eight inches long, by three or
four in diameter, mounted upon a horizontal axis, extending each way
beyond its ends for a distance about its own length.
“A spiral groove is cut in the circumference of the cylinder, from one
end to the other, each spiral of the groove being separated from its
neighbour by about one-tenth of an inch. The shaft or axis is also cut
by a screw thread corresponding to the spiral groove of the cylinder,
and works in screw bearings; consequently when the cylinder is caused
to revolve, by means of a crank that is fitted to the axis for this
purpose, it receives a forward or backward movement of about one-tenth
of an inch for every turn of the same, the direction, of course,
depending upon the way the crank is turned. The diaphragm is firmly
supported by an upright casting capable of adjustment, and so arranged
that it may be removed altogether when necessary. When in use, however,
it is clamped in a fixed position above or in front of the cylinder,
thus bringing the stylus always opposite the groove as the cylinder is
turned. A small, flat spring attached to the casting extends underneath
the diaphragm as far as its centre and carries the stylus, and between
the diaphragm and spring a small piece of india-rubber is placed
to modify the action, it having been found that better results are
obtained by this means than when the stylus is rigidly attached to the
diaphragm itself.
[Illustration: Fig. 194.—Mode of using the Telephone.]
“The action of the apparatus will now be readily understood from what
follows. The cylinder is first very smoothly covered with tin-foil, and
the diaphragm securely fastened in place by clamping its support to the
base of the instrument. When this has been properly done, the stylus
should lightly press against that part of the foil over the groove.
The crank is now turned, while, at the same time, someone speaks into
the mouthpiece of the instrument, which will cause the diaphragm to
vibrate, and as the vibrations of the latter correspond with the
movements of the air producing them, the soft and yielding foil will
become marked along the line of the groove by a series of indentations
of different depths, varying with the amplitude of the vibrations of
the diaphragm; or in other words, with the inflections or modulations
of the speaker’s voice. These inflections may therefore be looked upon
as a sort of visible speech, which, in fact, they really are. If now
the diaphragm is removed, by loosening the clamp, and the cylinder
then turned back to the starting point, we have only to replace the
diaphragm and turn in the same direction as at first, to hear repeated
all that has been spoken into the mouthpiece of the apparatus; the
stylus, by this means, being caused to traverse its former path, and
consequently, rising and falling with the depressions in the foil,
its motion is communicated to the diaphragm, and thence through the
intervening air to the ear, where the sensation of sound is produced.
[Illustration: Fig. 195.—BELL’S LONG-DISTANCE TELEPHONE
_a._ Compound magnet. _d._ Diaphragm. _e._ Speaking tube.
_f._ Telegraph wire. _g._ Line to earth. _b_, _c._ Small spaces.]
“As the faithful reproduction of a sound is in reality nothing more
than a reproduction of similar acoustic vibrations in a given time, it
at once becomes evident that the cylinder should be made to revolve
with absolute uniformity at all times, otherwise a difference more
or less marked between the original sound and the reproduction will
become manifest. To secure this uniformity of motion, and produce a
practically working machine for automatically recording speeches,
vocal and instrumental music, and perfectly reproducing the same, the
inventor devised an apparatus in which a plate replaces the cylinder.
This plate, which is ten inches in diameter, has a volute spiral groove
cut in its surface on both sides from its centre to within one inch of
its outer edge; an arm guided by the spiral upon the under side of the
plate carries a diaphragm and mouthpiece at its extreme end. If the
arm be placed near the centre of the plate and the latter rotated, the
motion will cause the arm to follow the spiral outward to the edge. A
spring and train of wheel-work regulated by a friction governor serves
to give uniform motion to the plate. The sheet upon which the record is
made is of tin-foil. This is fastened to a paper frame, made by cutting
a nine-inch disc from a square piece of paper of the same dimensions
as the plate. Four pins upon the plate pass through corresponding
eyelet-holes punched in the four corners of the paper, when the latter
is laid upon it, and thus secure accurate registration, while a
clamping-frame hinged to the plate fastens the foil and its paper frame
securely to the latter. The mechanism is so arranged that the plate may
be started and stopped instantly, or its motion reversed at will, thus
giving the greatest convenience to both speaker and copyist.
“The articulation and quality of the Phonograph, although not yet
perfect, is full as good as the Telephone was. The instrument, when
perfected and moved by clock-work, will undoubtedly reproduce every
condition of the human voice, including the whole world of expression
in speech and song, and will be used universally.
“The sheet of tin-foil or other plastic material receiving the
impressions of sound, will be stereotyped or electrotyped so as to be
multiplied and made durable; or the cylinder will be made of a material
plastic when used, and hardening afterward. Thin sheets of _papier
maché_, or of various substances which soften by heat, would be of this
character. Having provided thus for the durability of the Phonograph
plate, it will be very easy to make it separable from the cylinder
producing it, and attachable to a corresponding cylinder anywhere and
at any time. There will doubtless be a standard of diameter and pitch
of screw for Phonograph cylinders. Friends at a distance will then send
to each other Phonograph letters, which will talk at any time in the
friend’s voice when put upon the instrument.” (_Scribner._)
The MICROPHONE (an outcome of the Telephone) was discovered
by Professor Hughes, of London. It is an instrument which in its main
features consists of a carbon “pencil,” so suspended that one end rests
upon a carbon “die.” The instrument being connected with a Telephone
by the circuit wires, will reproduce faint sounds very distinctly.
Once a Microphone was put into a preacher’s pulpit, and joined to a
private telegraph wire which led to a gentleman’s house. The owner was
thus enabled to hear the sermon. So long as it is thus connected every
minute sound, even a fly’s footstep, will be faithfully reproduced.