either by connecting the wires which unite the telephones in
correspondence (near the receiving telephone) with branch wires of
other telephones, which may be done up to the number of five or six,
in short circuits; or by means of a little sounding-box closed by two
thin membranes, one of which is fixed on the vibrating disk. When a
certain number of acoustic tubes are connected with the membrane, Mr.
M’Kendrick asserts that several people can hear distinctly.
Telephones may also transmit speech to different stations
simultaneously, by inserting them on the same circuit, and experiments
made at New York showed that five instruments placed in different parts
of the same telegraphic line could be made to speak in this way. In
the telephonic experiments made on the canal lines in the department
of the Yonne, it was ascertained that on a wire seven miles and a
half in length, on which several telephones were placed at varying
distances, three or four persons were able to converse with each other
through the telephones, and each could hear what the other was saying.
The questions and answers could be understood, even in crossing. It
was also possible, by placing a telephone on a second wire, a little
over five miles in length, and half a yard distant from the other, to
hear the conversation exchanged on the first wire by following it to a
distance not exceeding a mile and a quarter. Even the different voices
of the two speakers could be distinguished.
Since the telephone made its appearance in Europe, several inventors
have asserted that they are able to make a telephone speak so as to be
audible in all parts of a large hall. It has been shown that this was
accomplished by Mr. Bell, and in this respect we do not see that those
who have attempted to improve the telephone have attained results of
greater importance. It is certain that the ordinary telephone can emit
musical sounds which become perfectly audible in a tolerably large
room, while the instrument is still attached to the wall. We should
also remember the results obtained by MM. Pollard and Garnier in the
experiments made at Cherbourg to connect the mole with the _Préfecture
Maritime_.
The mole at Cherbourg is, as we know, a kind of artificial island
thrown up before the town in order to make an anchorage. The forts
which have been constructed on the mole are connected by submarine
cables with the military port and with the _Préfecture Maritime_. On
one occasion, after making experiments in the Préfet’s study on one
of the cables applied to a telephone, several persons were talking
together in the room, and were much surprised to hear the bugle sound
the retreat, the sound appearing to come from one part of the room.
It was found, on examination, that the telephone hung to the wall was
occupied with this performance. On enquiry, it appeared that one of
the manipulators on the mole station had amused himself by sounding
the bugle before the telephone on that station. The mole is more than
three miles from Cherbourg, and the _Préfecture Maritime_ is in the
centre of the town. Yet these telephones had been roughly made in the
dockyard workshops; and we have here another proof of the small amount
of accuracy required for the successful working of these instruments.
[Illustration: FIG. 25.]
Telephones of various construction on the Bell model are to be seen at
M. C. Roosevelt’s, Mr. Bell’s agent in Paris, 1, Rue de la Bourse. They
are, for the most part, constructed by M. Bréguet, and the model in the
greatest request, exclusive of the one we have described, is the great
square model, with a horseshoe magnet enclosed in a flat box, and a
horn on its upper side, which serves as a mouthpiece. This system is
represented in fig. 25, and it has been neatly constructed at Boston
under the best conditions. In this new model, made by Mr. Gower, the
magnet is composed of several plates terminated by magnetic cores of
iron, to which the coils are fixed, and the whole is covered with a
thick layer of paraffin. The sounds thus reproduced are much stronger
and more distinct. Mr. Gower, who is now Mr. Roosevelt’s partner, has
made considerable improvements in the different forms of Mr. Bell’s
instrument. There is one model in the form of a snuff-box, in which
the magnet is twisted into a spiral, so as to maintain its length in
a circular form. The pole, which is in the centre of the spiral, is
furnished with an iron core, to which the induction coil is fastened,
and the cover of the snuff-box supports the vibrating disk as well
as the mouthpiece: this model is represented in fig. 26. In another
model, called the mirror telephone, the preceding arrangement is fitted
on to a handle like the glass of a portable mirror, and there is a
mouthpiece on one of the lateral faces, so that the speaker uses the
instrument as if he were speaking before a chimney screen.
[Illustration: FIG. 26.]
Mr. Bailey has different models of telephones worked by a battery or by
the Edison carbon of which we shall speak presently, and these, as well
as the telephones by Messrs. Gray and Phelps, are more successful in
conveying sound on a long line of wire.
DIFFERENT ARRANGEMENTS OF TELEPHONES.
The prodigious results attained with the Bell telephones, which were
at first discredited by many scientific men, necessarily provoked,
as soon as their authenticity was proved, innumerable researches on
the part of inventors, and even of those who were originally the most
incredulous. A host of improvements and modifications have consequently
been suggested, which are evidently not without interest, and must now
be considered by us.
BATTERY TELEPHONES.
_The Edison Telephone._--One of the earliest and most interesting
improvements made in the Bell telephone is that introduced by Mr.
Edison in the early part of the year 1876. This system is indeed more
complicated than the one we have just considered, since it requires
a battery, and the sending instrument differs from the receiving
instrument; but it is less apt to be affected by external causes, and
transmits sound to a greater distance.
The Edison telephone, like Mr. Gray’s, which we have already had
occasion to mention, is based upon the action of undulatory currents,
determined by the variations in the resistance of a conductor of
moderate conducting power, which is inserted in the circuit, and the
vibrations of a diaphragm before which the speaker stands react upon
it. Only, instead of employing a liquid conductor, which is practically
useless, Mr. Edison has attempted to use semi-conducting solid
bodies. Those which were most suitable from this point of view were
graphite and carbon, especially the carbon extracted from compressed
lamp-black. When these substances are introduced into a circuit between
two conducting plates, one of which is moveable, they are capable of
modifying the resistance of the circuit almost in the same proportion
as the pressure exerted upon them by the moveable plate,[5] and it
was seen that, in order to obtain the undulatory currents necessary
for the production of articulate sounds, it was enough to introduce
a disk of plumbago or of lamp-black between the vibrating plate of a
telephone and a platinum plate placed in connection with the battery.
When the telephone disk is placed in circuit, its vibrations before
the disk of carbon produce a series of increasing and decreasing
pressures, thus causing corresponding effects in the intensity of the
transmitted current, and these effects react in an analogous manner on
the undulatory currents determined by induction in the Bell system. In
order to obtain good results, however, several accessory arrangements
were necessary, and we represent in fig. 27 one of the arrangements
made in this part of Mr. Edison’s telephonic system.
[Illustration: FIG. 27.]
In this figure a section of the instrument is given, and its form
greatly resembles that of Bell. L L is the vibrating disk; O′ O, the
mouthpiece; M, the opening to the mouthpiece; N N N, the case for the
instrument, which is, like the mouthpiece, made of ebonite, and below
the disk it presents a rather large cavity, and a tubular hole which
is scooped in the handle. In its upper part this tube terminates in a
cylindrical rim, furnished with a worm on which is screwed a little
rod with a ridge on its inner side, and the rheostatic system is
placed within this tube. The system consists, first, of a piston E,
fitted to the end of a long screw E F, and the turning of the button
will move the piston up or down within a certain limit. Above this
piston there is fitted a very thin platinum plate A, connected by a
flexible chain and a wire with a binding-screw P′. Another plate B,
exactly similar, is connected with the binding-screw P, and the carbon
disk C is placed between these two plates. This disk is composed of
compressed lamp-black and petroleum, and its resistance is one _ohm_,
or 110 yards, of telegraphic wire. Finally, an ebonite disk is fastened
to the upper platinum plate, and an elastic pad, composed of a piece
of caoutchouc tube G, and of a cork disk H, is interposed between the
vibrating plate L L and the disk B, in order that the vibrations of
the plate may not be checked by the rigid obstacle formed by the whole
rheostatic system. When these different parts are in position, the
instrument is regulated by the screw F, and this is easily done by
screwing or unscrewing it until the receiving telephone gives out its
maximum of sound.
[Illustration: FIG. 28.]
In another model, represented in fig. 28, which has produced the best
results in the distinctness with which sounds are transmitted, the
vibrating plate L L is supported on the disks of the secondary carbon
conductor C by means of a little iron cylinder A, instead of the
caoutchouc pad, and the pressure is regulated by a screw placed below
_e_. The mouthpiece E of the instrument is more prominent, and its
opening is larger. Finally, the instrument, which is cased in nickel
silver, is without a handle. The rigid disk _b_, resting on the first
platinum plate _p_, is of aluminium instead of ebonite.
[Illustration: FIG. 29.]
The receiving telephone somewhat resembles that of Mr. Bell, yet it
presents some differences which can be understood from the examination
of fig. 29. The magnet N S is horseshoe in form, and the magnetising
coil E only covers one of the poles, N: this pole is precisely in
the centre of the vibrating plate L L, while the second pole is near
the edge of this plate. The size of the plate itself is considerably
reduced: its superficies is about the same as that of a five-franc
piece, and it is enclosed in a kind of circular groove, which keeps
it in a definite position. In consequence of this arrangement the
handle of the instrument is of solid wood, and the vacant space for
the electro-magnetic system is somewhat larger than in the Bell model;
but an arrangement is made for subduing the echo, and there is a kind
of sounding-box to magnify the sound. It is evident that the relation
which the electro-magnetic system bears to the vibrating disk must
increase the sensitiveness of the instrument; for as the pole S is in
close contact with the disk L L, the latter is polarised, and becomes
more susceptible to the magnetic influence of the second pole N, which
is separated from it by an interval not exceeding the thickness of a
sheet of coarse paper. In Mr. Edison’s two instruments, the receiver
and sender, the upper part C C, corresponding to the vibrating disk,
instead of being fixed by screws to the handle, is screwed on to the
handle itself, which makes it much more easy to dismount the instrument.
Mr. Edison has varied the form of his instruments in many ways, and
their cases have of late been made of metal with a funnel-shaped
mouthpiece of ebonite.
When Mr. Edison had ascertained, as indeed Mr. Elisha Gray had done
before him, that induced currents are more favourable to telephonic
transmissions than voltaic currents, he transformed the currents from
the battery which passed through his sender into induced currents by
making them pass through the primary circuit of a carefully insulated
induction coil; the line wire was then put into communication with
the secondary wire of the coil. We shall afterwards describe some
experiments which show the advantages of this combination: for the
present we can only point out the fact, for it is now an integral
quality of almost all the systems of battery telephones.
_Edison’s Chemical Telephone._--The curious and really useful effects
produced by Mr. Edison with his _electro-motograph_ prompted, about the
beginning of the year 1877, his idea of applying the principle of this
instrument to the telephone for the reproduction of transmitted sounds;
and he obtained such interesting results that the author of an article
on telephones, published in the ‘Telegraphic Journal,’ August 15, 1877,
put forward this invention as one of the finest of the nineteenth
century. It certainly appears to have given birth to the phonograph,
which has lately become famous, and has so much astonished men of
science.
To understand the principle of this telephone, we must give some
account of Mr. Edison’s electro-motograph, discovered in 1872. This
instrument is based upon the principle that if a sheet of paper,
prepared with a solution of hydrate of potash, is fastened on a
metallic plate which is united to the positive pole of a battery, and
if a point of lead or platinum connected with the negative pole is
moved about the paper, the friction which this point encounters ceases
after the passage of the current, and it is then able to slide as if
upon a mirror until the current is interrupted. Now, as this reaction
may be effected instantaneously under the influence of extremely weak
currents, the mechanical effects produced by these alternations of
arrest and motion may, by a suitable arrangement of the instrument,
determine vibrations in correspondence with the interruptions of
current produced by the transmitter.
In this system the telephonic receiver consists of a resonator and a
drum mounted on an axis and turned by a winch. A paper band, wound
upon a reel, passes over the drum, of which the surface is rough, and
a point tipped with platinum, and fitted to the end of a spring which
is fixed in the centre of the resonator, presses strongly on the paper.
The current from the battery, first directed on the spring, passes
by the platinum point through the chemical paper, and returns by the
drum to the battery. On turning the winch, the paper moves forward,
and the normal friction which is produced between the paper and the
platinum point pushes the point forward, while producing by means
of the spring a tension on one side of the resonator; but since the
friction ceases at each passage of the current through the paper, the
spring is no longer drawn out, and the resonator returns to its normal
position. Since this double effect is produced by each vibration made
in the sender, a series of vibrations takes place in the resonator,
repeating those of the sender, and consequently the musical sounds
which affected the sender are reproduced to a certain extent. According
to the American journals, the results produced by this instrument
are astonishing: the weakest currents, which would have no effect
on an electro-magnet, become perfectly efficacious in this way. The
instrument can even reproduce with great intensity the highest notes of
the human voice, notes which can hardly be distinguished by the use of
electro-magnets.
The sender nearly resembles the one we have previously described,
except that, when it is used for musical sounds, a platinum point
is employed instead of the disk of carbon, and it ought not to be
in constant contact with the vibrating plate. According to the
‘Telegraphic Journal,’ it consists simply of a long tube, two inches
in diameter, having one end covered with a diaphragm formed of a thin
sheet of copper, and kept in its place by an elastic ring. A small
platinum disk is riveted to the centre of the copper diaphragm, and a
point of the same metal, fitted with a firm support, is adjusted before
the disk. When the singer stands before the diaphragm, its vibration
causes it to touch the platinum point, and produces the number of
breaks in the current which corresponds to the vibration of the notes
uttered.
The experiments lately made in America, in order to decide on the
merits of various telephonic systems, show that Mr. Edison’s telephone
gives the best results. The ‘Telegraphic Journal,’ May 1, 1878, states
that on April 2 Mr. Edison’s carbon telephone was tested between New
York and Philadelphia on one of the numerous lines of the West Union.
The length of the line was 106 miles, and ran parallel to other wires
almost throughout its length. The effects of induction caused by
telegraphic transmissions through the adjacent wires were enough to
make speech inaudible through the other telephones, but they had no
influence on Edison’s telephone, which was worked with a battery of two
cells and a small induction coil, and Messrs. Batchelor, Phelps, and
Edison were able to converse with ease. Mr. Phelps’ magnetic telephone,
which is considered to be the most powerful of its kind, did not afford
such good results.
In the experiments made between the Paris Exhibition building and
Versailles, the jury commission was able to ascertain that the results
were equally favourable.
_Telephones by Colonel Navez._--Colonel Navez of the Belgian Artillery,
inventor of the well-known balistic chronograph, has endeavoured to
improve the Edison telephone by employing several disks of carbon
instead of one. He considers that the variations of electric resistance
produced by carbon disks under the influence of unequal pressure
depend chiefly on their surface of contact, and he consequently
believes that the more these surfaces are multiplied, the greater
the differences in question will be, just as it happens when light
is polarised through ice. He adds that these disks act well by their
surfaces of contact, since, if they are separated by copper disks, the
speech reproduced ceases to be articulate.[6]
I am not surprised to learn that Colonel Navez has found a limit to the
number of carbon disks, for the reproduction of speech in this system
is due both to the greatness of the differences of resistance in the
circuit, and to the intensity of the transmitted current. If therefore
the instrument’s sensitiveness to articulate sounds is increased
by increasing the number of imperfect contacts in the circuit, the
intensity of the transmitted sounds is diminished, and thus sounds lose
their power. There is consequently a limit to be observed in the number
of carbon disks placed upon each other; and it depends on the nature of
the imperfect contacts which are employed, and on the tension of the
electric generator.
In order to stop the unpleasant musical vibrations which accompany
telephonic transmissions, Colonel Navez employs for the vibrating plate
of the sender a silver-plated copper disk, and for the vibrating plate
of the receiver an iron disk lined with brass and soldered together. He
also employs caoutchouc tubes with mouthpieces and ear-tubes for the
transmission and reception of sound, and these instruments are placed
level on a table. For this purpose the magnetised bar of the receiving
telephone is replaced by two horizontal magnets, acting through a pole
of the same nature on a little iron core which carries the coil, and
which is placed vertically between the two magnets. He necessarily
makes use of a small Ruhmkorff coil to transform the electricity of the
battery into induced electricity.
[Illustration: FIG. 30.]
[Illustration: FIG. 31.]
Figs. 30 and 31 represent the two parts of this telephonic system. The
carbon battery is in C (fig. 30), the vibrating disk in L L, and the
mouthpiece E, fitted to a caoutchouc tube T E, corresponds at the lower
end to the vibrating disk. The carbon battery is placed in metallic
contact with the circuit by a platinum rod E C, and the vibrating disk
also communicates with the circuit through a binding-screw. In the
receiving telephone (fig. 31) the upper part is arranged much as in
the ordinary telephones, except that, instead of a mouthpiece, the
instrument is fitted with an ear-tube T O. The two horseshoe magnets,
A, A, which communicate a uniform polarity to the iron core N, support
the induction coil B. The two terminals of this receiver are connected
with the supplementary wire of the induction coil, and the two
terminals of the sender are connected with the two ends of the primary
of this coil, and with the battery which is inserted in the circuit
near this instrument.
_The Pollard and Garnier Telephones._--The battery telephone made
by MM. Pollard and Garnier differs from the foregoing in this
particular: it simply employs two points of graphite, mounted in
metallic porte-crayons, and these points are directly applied against
the vibrating plate with a pressure which must be regulated. Fig. 32
represents the arrangement adopted, which, however, may be infinitely
varied.
L L is the vibrating tin plate, above which is the mouthpiece E, and
P, P′ are the two graphite points with their porte-crayons. There is a
screw on the lower part of the porte-crayons which is fixed in a hole
pierced in a metallic plate C C, and by this means the pressure of the
pencils against the disk L L can be regulated. The metallic plate C C
is made in two pieces, placed side by side, but insulated from each
other, so that they may be placed in communication with a cylindrical
commutator, and by its means the circuit can be arranged in different
ways. Since the commutator consists of five sheets, the transition from
one combination to another is instantaneous, and these combinations are
as follows:
1. The current enters by the pencil P, passes into the plate, and so to
line.
2. The current enters by the pencil P′, passes into the plate, and so
to line.
3. The current comes simultaneously by the two pencils P and P′, goes
into the plate, and thence to line.
4. The current comes by the pencil P, goes thence to the plate, then
into the pencil P′, and so to line.
[Illustration: FIG. 32.]
By this means there are two elements of combination, which may be
employed separately, or by coupling them for tension or quantity.
When the pencils are properly regulated and give a regular transmission
of equal intensity, the effects produced in the transition from
one combination to another may be easily studied, and it has been
ascertained: first, that in a short circuit there is no appreciable
change, whatever be the combination employed; secondly, that when the
circuit is long, or of great resistance, the tension arrangement is the
best, and this in proportion to the length of the line.
This telephonic system, like the two preceding ones, requires an
inducing machine to transform voltaic into induced currents: we shall
presently speak of this important accessory of these instruments.
Besides this arrangement, MM. Pollard and Garnier have employed the one
we have represented in fig. 5, which has given better results. We shall
see presently that it can be used as the receiving organ of sounds. In
each case the two carbons must be placed in contact, and subjected to a
certain initial pressure, which should be regulated by the screw fitted
to the support of the lower carbon.
As for the receiving telephone, the arrangement adopted by MM. Pollard
and Garnier is the same as Bell’s, except that they employ tin plates
and helices of greater resistance. This resistance ranges in fact
from 100 to 125 miles. ‘We have always held,’ these gentlemen say,
‘that whatever may be the resistance of the outer circuit, there is an
advantage in increasing the number of spirals, even when using wire
No. 42, which is the one we prefer.’
[Illustration: FIG. 33.]