second edition of my _Exposé des applications d’Electricité_, I pointed
them out in speaking of the contact-breakers. I also spoke of them in
a paper on electro-magnets (published in the _Annales télégraphiques_,
1865), and in several articles laid before the _Académie des Sciences_
in 1872 and 1875 on the conductivity of filings and conducting powders.
M. Clérac, in 1865, also used them to obtain variable resistances.
[6] In 1865 I was able to verify this observation when tightening the
spirals of an electro-magnet on a naked wire. The greater the number
of spirals under pressure, the more definite were the differences of
resistance in the magnetising helix.
[7] M. Hellesen communicated the plan of his instrument to me on May 3,
1878, and his experiments were made in Copenhagen three weeks earlier.
[8] M. M. J. Page had already noticed that if a telephone is placed
in the circuit of the primary helix of an induction coil, while the
secondary helix of this instrument is placed in the circuit of one of
M. Lippmann’s capillary electrometers, a movement of the mercurial
column of the electrometer takes place at each word, and this movement
is effected towards the capillary end of the tube, in whatever
direction the current is sent by the telephone. This is because the
mercury always tends to move more rapidly at its capillary end than at
the other extremity.
[9] Mr. Edison, in a letter written November 25, 1877, writes that
he has made two telephones which act with copper diaphragms, based
on Arago’s effects of magnetism by rotation. He ascertained that a
copper diaphragm might replace the iron plate, if its thickness did not
exceed 1/32 of an inch. The effect produced is slight when the copper
diaphragm is placed between two corresponding instruments; but when the
sender only is furnished with the copper diaphragm, and the receiver is
arranged as usual, communication becomes easy.
Mr. Preece repeated these experiments, but he only obtained very slight
and indistinct effects: he consequently believes that they are of no
practical use, although very interesting in theory.
[10] Mr. Bell had previously made a like experiment, which suggested to
him that molecular vibrations had as much to do with the action of the
telephone as mechanical vibrations.
[11] M. Bosscha, who has published in the _Archives néerlandaises_
an interesting paper on the intensity of electric currents in the
telephone, says that the minimum intensity of currents necessary to
produce a sound in a telephone by the vibration of its diaphragm may
be less than 100/1000 of a Daniell element, and the displacement of
the centre of the diaphragm would then be invisible. He was unable
to measure exactly the range of movements produced in the diaphragm
by the influence of the voice, but he believes it to be less than
the thousandth part of a millimètre; and from this it follows that,
for a sound of 880 vibrations, the intensity of the induced currents
developed would be 0·0000792 of the unit of electro-magnetic intensity.
[12] Mr. Warwick describes his experiments as follows: ‘The magnets
employed were nearly of the usual size, 1½ inch in diameter, and nearly
eight times as long. At first I employed iron disks, but I found
them to be unnecessary. When I had discarded them, I tried several
substances: first a thin disk of iron, which answered perfectly both
for sender and receiver. A disk of sheet iron, about ⅒ of an inch
in thickness, did not act so well, but all that was said was quite
understood. In making experiments with the disks, I simply placed them
above the instrument, without fixing them in any way: the wooden cover
and the conical cavity were also laid aside, because the transmission
and reception could be effected as well without them. This part of the
instrument seems to be superfluous, since, when the disk is simply
placed level to the ear, the sound seems to be increased by being
brought nearer. Although iron acts better than anything, it appears
that iron disks are not absolutely necessary, and that diamagnetic
substances also act perfectly. I wished that my assistant, who was at
some distance, and could not hear any direct sound, should continue
his calculations. I took away the iron disk and placed across the
instrument a wide iron bar, an inch thick. On applying my ear to it, I
could hear every sound distinctly, but somewhat more faintly. A piece
of copper, three inches square, was substituted for it: although the
sound was still distinct, it was fainter than before. Thick pieces of
lead, zinc, and steel were alternately tried. The steel acted in almost
the same way as the iron, and, as in the other cases, each word was
heard faintly but distinctly. Some of these metals are diamagnetic,
and yet the action took place. Some non-metallic substances were next
tried; first a piece of window-glass, which acted very well. The action
was faint with a piece of a wooden match-box; but on using pieces
of gradually increasing thickness the sound was sensibly increased,
and with a piece of solid wood, 1½ inch in thickness, the sound was
perfectly distinct. I next replaced it by an empty wooden box, which
acted very well. A piece of cork, ½ inch thick, acted, but somewhat
faintly. A block of razor-stone, 2 inches thick, was placed upon the
instrument; and, on applying the ear to it, it was quite easy to
follow the speaker. I then tried to hear without the insertion of any
substance, and, on applying my ear quite close to the coil and magnet,
I heard a faint sound, and on listening attentively I understood all
that was said. In all these experiments the sounds were perceived,
but the sounds transmitted or attempted did not act precisely alike.
The sound of a tuning-fork, placed on the iron disk itself or on
the case of the instrument, was clearly heard: thin iron disks were
more effective for articulate speech. With other substances, stone,
solid wood, glass, zinc, &c., the sound of the tuning-fork was heard,
whether it rested upon them, or the vibrating fork was held above
them. These substances were not adapted for transmitting the sound
of the voice. These were all laid aside, and the sounding instrument
was held directly above the pole of the magnet: the sound was clearly
heard, although there was nothing but air between the end of the
magnet and the tuning-fork. The sound was perhaps less intense when
the tuning-fork was held directly above the pole, than when it was at
the end of the magnet. I next tried if my voice could be heard with
this arrangement. The result was rather doubtful, but I think that
some action must have taken place, for the tuning-fork was heard when
it was simply vibrated near the pole. The effect of the voice can only
have differed in the degree of intensity: it was too faint to be heard
at the other extremity. I repeated these effects; I assured myself of
them, and I succeeded in transmitting sounds distinctly on the pole
without a disk, and, on the other hand, by applying my ear to the
instrument, I was able to hear distinctly all that was said, although
there was no disk.’
[13] These are his own words: ‘The articulation produced from the
instrument was remarkably clear, but its great defect consisted in the
fact that it could not be used as a sending instrument, and thus two
telephones were required at each station, one for transmitting and one
for receiving spoken messages.’
[14] These carbons are made by heating, in a temperature gradually
raised to white heat, fragments of deal of a close fibre, which is
enclosed in an iron tube or box hermetically sealed.
[15] Mr. Willoughby Smith varied this experiment by placing a packet
of silk threads coated with copper on the disconnected ends of the
circuit, which were arranged at right angles with each other. Under
these conditions the instrument became so sensitive, that the current
of air produced by a lamp placed above the system, caused a decided
crackling noise in the telephone.
[16] Mr. Hughes observes on this subject that carbon is a valuable
material for such purposes, since it does not oxidise, and its effects
are greater when combined with mercury. He takes the prepared charcoal
used by artists, brings it to a white heat, and suddenly plunges it in
a bath of mercury, of which the globules instantly penetrate the pores
of charcoal, and may be said to metallise it. He also tried charcoal
coated with a deposit of platinum, or impregnated with chloride of
platinum, but this was not more successful than the former method. If
the charcoal of fir-wood is brought to a white heat in an iron tube,
containing tin and zinc, or any other metal which readily evaporates,
it is metallised, and is adapted for use if the metal is subdivided in
the pores of charcoal and not combined with it. When iron is introduced
into carbon in this way it is one of the most effective metals. The
charcoal of fir-wood, in itself a bad conductor, may thus acquire great
conducting power.
[17] Mr. Hughes remarks that the vibrations which affect the
microphone, even in speaking at a distance from the instrument, do
not proceed from the direct action of the sound waves on the contacts
of the microphone, but from the molecular vibrations produced by it
on the board which serves to support the instrument; he shows, in
fact, that the intensity of sounds produced by the microphone is in
proportion to the size of the surface of this board, and when the
sending microphone is enclosed in a cylindrical case, its sensitiveness
is not much diminished if the surface of the box enclosing the whole is
sufficiently large. From this point of view he has sought to increase
the sensitiveness of his instruments by fixing the frame on which the
moveable parts of the sender and receiver revolve on a spring plate.
[18] Helmholtz’s resonator is based upon the principle that a volume
of air contained in an open vase emits a certain note when placed in
vibration, and that the height of the note depends on the size of the
vase and of its opening. Helmholtz makes use of a globe with a large
opening on one side and a small one on the other, and the small one is
applied to the ear. If a series of musical notes take place in the air,
the one which is in harmony with the fundamental note of the globe is
intensified, and can be distinguished from the rest. The same effect
takes place when, on singing to a piano accompaniment, some strings are
heard to vibrate more strongly than others, namely, those which vibrate
in unison with the sounds emitted. The resonators are made in various
ways; those most generally used are cases of different lengths which
also serve as sounding-boxes.
[19] I give the text of M. Cros’ sealed paper, opened by his request,
at the Académie des Sciences, December 3, 1877:--‘Speaking generally,
my process consists in obtaining traces of the movement to and fro of
a vibrating membrane, and in using this tracing to reproduce the same
movements, with their intrinsic relations of duration and intensity,
either on the same membrane or on one adapted to give out the sounds
which result from this series of movements.
‘It is therefore necessary that an extremely delicate tracing, such as
may be obtained by passing a needle over a surface blackened by fire,
should be transformed into a tracing, capable of sufficient resistance
to guide an index which will transmit its movements to the membrane of
sound.
‘A light index is fastened to the centre of a vibrating membrane; it
terminates in a point (a metallic wire or tip of a feather) which rests
on a surface which has been blackened by fire. This surface forms part
of a disk, to which the double action of rotation and rectilinear
progression has been given. If the membrane is at rest, the point
will trace a simple spiral; if the membrane vibrates, there will be
undulations in the spiral, and these undulations will represent the
precise movements of the membrane in their duration and intensity.
‘By a well-known photographic process a transparent tracing of the
undulations of the spiral can be represented by a line of similar
dimensions on some resisting substance, tempered steel for example.
‘When this is done, this resisting surface is placed in a turning
machine which causes it to revolve and advance with a velocity and
motion similar to those by which the registering surface was actuated.
A metallic point if the tracing is concave, or a grooved index if it
is in relief, is kept upon the tracing by a spring, and the index
which supports this point is connected with the centre of the membrane
which produces the sounds. Under these conditions, the membrane will
be actuated not by the vibrating air, but by the tracing which guides
the index, and the impulses will be precisely similar in duration and
intensity to those to which the registering membrane was subjected.
‘The spiral tracing represents equal successions of time by increasing
or decreasing lengths. There is no inconvenience in this, since the
turns of the spiral are very close together, if only the circumference
of the turning circle is used; but then the central surface is lost.
‘In all cases the tracing of the helix on a cylinder is much more
satisfactory, and I am now trying to make this idea practicable.’
[20] Never make a contact between the stylus and the cylinder until the
latter is covered with the tinfoil. Do not begin to turn the cylinder
until assured that everything is in its place. Take care, when the
stylus returns to the point of departure, to bring the mouthpiece
forward. Always leave a margin of from five to ten millimètres on the
left and at the beginning of the sheet of tinfoil; for if the stylus
describes the curve on the extreme edge of the cylinder, it may tear
the sheet or come out of the groove. Be careful not to detach the
spring of the caoutchouc pad.
To fix the tinfoil, apply varnish to the end with a paint-brush; take
this end between the finger and thumb of the left hand, with the sticky
part towards the cylinder; raise it with the right hand and apply it
quite smoothly to the cylinder; bring round the sticky end, and join
them firmly.
To adjust the stylus and place it in the centre of the groove, bring
the cylinder to the right, so as to place the stylus opposite the
left extremity of the tinfoil; bring forward the cylinder gently and
by degrees, until the stylus touches the tinfoil with force enough to
imprint a mark. Observe if this mark is quite in the centre of the
groove (in order to do this, make a mark with the nail across the
cylinder), and if it is not, adjust the stylus to the right or left by
means of the little screw placed above the mouthpiece. The depth of the
impression made by the stylus should be ⅓ millimètre, just enough for
it to leave a slight tracing, whatever the range of vibrations may be.
To reproduce the words, the winch must be turned with the same velocity
as when they were inscribed. The average velocity should be about
eighty turns a minute.
In speaking, the lips must touch the mouthpiece, and deep guttural
sounds are better heard than those which are shrill. In reproducing,
the tightening screw must be loosened and brought in front of the
mouthpiece, the cylinder must be brought back to its point of
departure, the contact between the stylus and the foil must be renewed,
and the cylinder must again be turned in the same direction as when the
sentence was spoken.
To increase the volume of reproduced sound, a tube of cardboard, wood,
or horn may be applied to the mouthpiece; it must be of a conical form,
and its lower end should be rather larger than the opening of the
mouthpiece.
The stylus consists of a No. 9 needle, somewhat flattened on its two
sides by friction on an oiled stone. The caoutchouc pad which connects
the plate with the disk serves to weaken the vibrations of the plate.
If this pad should come off, heat the head of a small nail, apply it to
the wax which fastens the pad to the plate or to the spring, so as to
soften it; then press the caoutchouc lightly, until it adheres to the
place from which it was detached. The pads must be renewed from time to
time, as they lose their elasticity. Care must be taken in replacing
them not to injure the vibrating plate, either by too strong a pressure
or by grazing it with the instrument employed to fix the pad.
The first experiments should be with single words or very short
sentences, which can be extended as the ear becomes accustomed to the
instrument’s peculiar tone.
The tone is varied by accelerating or slackening the rotatory movement
of the cylinder. The cries of animals may be imitated. Instrumental
music may be reproduced by placing a cardboard tube before the
mouthpiece. The airs should be played in rapid time, since, when there
is no system of clockwork, they will be more perfectly reproduced than
those which are played slowly.
[21] We confess that we find it difficult to believe in this property
of the phonograph, from which we have only heard the harsh and
unpleasant voice of Punch.
[22] The action of this pedal is effected by two little rockers, so
connected that the upper damper is lowered a little before the lower
damper is raised--a condition necessary to produce the quivering motion
of the plate which furnishes the rolling _r_.
[23] The arrangement of this part of the instrument is remarkable in
this particular, that in the case of certain letters the air is ejected
with more or less force through the pipe I, while in the case of other
letters the air is drawn into the same tube. Since I was unable to
see the internal arrangement of these cavities, I can only give an
imperfect account of the mechanism at work.
Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.
Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.
Illustrations in this eBook have been positioned between paragraphs and
outside quotations.
Footnotes, originally at the bottoms of the pages that referenced them,
have been collected, sequentially renumbered, and placed near the end
of the book.
The Table of Contents is not well-coordinated with the actual text. The
Transcriber has not added missing entries, but has attempted to correct
page number discrepancies.
Several diagrams use labels with prime marks, but the accompanying
explanations do not always include the prime marks.