made them the subject of four papers which were laid before the
Académie des Sciences in 1872, and I am convinced that they have in
general nothing to do with atmospheric electricity, but result either
from thermo-electric or hydro-electric influence. They take place
constantly and in all weathers on telegraph lines, whether these lines
are insulated at one end, or in contact with the earth at both ends.
In the first case, the polar electrodes of the couple are formed by
the telegraph wire and the earth plate, generally of the same nature,
and the intermediate conducting medium is represented by the posts
which support the wire and the earth which completes the circuit. In
the second case, the couple is formed in almost the same way, but
the difference in the chemical composition of the ground at the two
points where the earth plates are buried, and sometimes their different
temperature, exert a strong influence. If only the first case be
considered, it generally happens that on fine summer days the currents
produced during the day are inverse to those which are produced by
night, and vary with the surrounding temperature in one or the other
direction. The presence or absence of the sun, the passage of clouds,
the currents of air involve abrupt and strongly marked variations,
which may be easily followed on the galvanometer, and which cause more
or less distinct sounds in the telephone.
During the day, the currents are directed from the telegraph line to
the earth plate, because the heat of the wire is greater than that of
the plate, and these currents are then thermo-electric. During the
night, on the other hand, the wire is cooled by the dew, which causes a
greater oxidation on the wire than that which takes place on the plate,
and the currents then become hydro-electric.
I say more about these currents because, in consequence of a mistaken
belief as to their origin, it has been supposed that the telephone
might serve for the study of the variations of the atmospheric
electricity generally diffused through the air. Such an application of
the telephone would, under these conditions, be not only useless, but
also misleading, by inducing the study of very complex phenomena, which
could lead to nothing more than I have already stated in my different
papers on the subject.
Certain local influences will also produce sounds in the telephone.
Thus the distension of the diaphragm by the moist heat of the breath,
when the instrument is held before the mouth in speaking, causes a
perceptible murmur.
From the electro-static reactions, so strongly produced on the
submarine cables, in consequence of electric transmissions, it might be
supposed that it would not be easy to hold telephonic correspondence
through this kind of conductor, and, to ascertain the fact, an
experiment was made on the cable between Guernsey and Dartmouth, a
distance of sixty miles. Articulate speech, only a little indistinct,
was, however, perfectly transmitted. Other experiments, made by
Messrs. Preece and Wilmot, on an artificial submarine cable, placed
in conditions analogous to those of the Atlantic cable, showed that a
telephonic correspondence might be kept up at a distance of a hundred
miles, although the effects of induction were apparent. At the distance
of 150 miles, it was somewhat difficult to hear, and the sounds were
very faint, as if some one were speaking through a thick partition. The
sound diminished rapidly until the distance of 200 miles was reached,
and after that it became perfectly indistinct, although singing could
still be heard. It was even possible to hear through the whole length
of the cable, that is, for 3,000 miles, but Mr. Preece believed this to
be due to the induction of the condenser on itself: he holds, however,
that singing may be heard at a much greater distance than speech,
owing to the more regular succession of electric waves.
Mr. Preece also made experiments on the subterranean telegraphs
between Manchester and Liverpool, a distance of 30 miles, and found
no difficulty in exchanging correspondence; and it was the same with
the cable from Dublin to Holyhead, a distance of 67 miles. This cable
had seven conducting wires, and when the telephone was connected with
one of them, the sound was repeated through all the others, but in a
fainter degree. When the currents of the telegraphic instruments passed
through the wires, the induction was apparent, but not so great as to
prevent telephonic communication.
ESTABLISHMENT OF A TELEPHONIC STATION.
Although the telephonic system of telegraphy is very simple, yet
certain accessory arrangements are indispensable for its use. Thus,
for example, an alarum call is necessary, in order to know when the
exchange of correspondence is to take place, and information that
the call has been heard is likewise necessary. An electric bell is
therefore an indispensable addition to the telephone, and since the
same circuit may be employed for both systems, if a commutator is
used, it was necessary to find a mode of making the commutator act
automatically, so as to maintain the simple action of the system which
constitutes its principal merit.
_MM. Pollard and Garnier’s System._--With this object, MM. Pollard and
Garnier devised a very successful arrangement last March, which employs
the weight of the instrument to act upon the commutator.
For this purpose, they suspended the instrument to the end of a spring
plate, fastened between the two contacts of the commutator. The circuit
wire corresponds with this plate, and the two contacts correspond, the
one with the telephone, the other with the bell. When the telephone
hangs below the spring-support, that is, when it is not at work,
its weight lowers the spring plate on the lower contact, and the
communication of the line with the bell is established: when, on the
other hand, the telephone is raised for use, the spring plate touches
the higher contact, and communication is established between the line
and telephone. In order to make the bell sound, it is only necessary to
establish, on the wire which connects the line with the bell contact of
the commutator, a breaker which can both join and break the current,
and which communicates on one side with the contact of the bell, and
on the other with its battery. The ordinary push of an electric bell
will be sufficient, if it is supplied with a second contact, but MM.
Pollard and Garnier wished to make this action also automatic, and
consequently they devised the arrangement represented in fig. 53.
[Illustration: FIG. 53.]
In this system, as well as in those which have since been devised, two
telephones are employed, one of which is constantly applied to the ear,
and the other to the mouth, so as to make it possible to speak while
listening. The telephones are supported by three wires, two of which
contain flexible conductors, while the third only acts as a support.
Two of the four wires of the two telephones are connected with each
other, and the other two are connected with the two binding screws of
the commutator _t_, _t′_: the wires without conductors are suspended to
the extremities of the two flexible plates _l_, _l′_, which correspond
with earth and line.
When at rest, the weight of the telephones presses the two plates _l_,
_l′_, on the lower contacts S, S′, but when the instruments are taken
up these plates press against the higher contacts.
The two bell wires terminate on the lower contacts, those of the
telephones on the higher contacts, and one of the poles of the battery
is connected with the lower contact on the left S′, the other with the
higher contact on the right T.
When at rest, the system is applied to the electric bell, and the
current sent from the opposite station will follow the circuit L _l_
S S′ S′ _l′_ T, so that the call will be made. On taking up the two
telephones, the circuit of the bell system is broken, and that of the
telephones is established, so that the current follows the course L
_l_ T _t t′_ T′ _l′_ T. If only one telephone is held at a time, the
current is sent into the bell system of the opposite station, and
follows the route + P S _l_ L T _l′_ T′ _t_ P --. In this way the
three actions necessary for calling, corresponding, and enabling the
corresponding instrument to give a call, are almost involuntarily made.
_System by MM. Bréguet and Roosevelt._--In the system established by
the Paris agents of the Bell company, the arrangement resembles the
one just described, except that there is only one spring commutator,
and the call is made with the push of an ordinary electric bell. A
mahogany board is suspended from the wall, and on it are arranged,
first, the ordinary electric bell system, with a sending push fixed
below it; second, two forks supporting two telephones, one of which is
fastened to the bar of a commutator, arranged as a Morse key. The two
telephones are connected by two conducting wires, so arranged as to
be capable of extension, and two of their four binding screws are in
immediate connection with each other, and the other two with the earth,
line, and battery, by means of the commutator, the sending push, and
the bell system. The arrangement is shown in fig. 54.
[Illustration: FIG. 54.]
The commutator A consists of a metallic bar _a c_, bearing the
suspension fork of one of the telephones F′ below its point of
articulation: it ends in two pins _a_ and _c_, below which the two
contacts of the commutator are fixed, and a spring compresses the
lower arm of the bar, so as to cause the other arm to rest constantly
on the higher contact. For greater security a steel tongue _a b_ is
fastened to the lower end of the bar, and rubs against the small shaft
_b_, which is provided with two insulated contacts, corresponding to
those of the board. The bar is in communication with the line wire
by means of the call-push, and the upper of the two contacts we have
just described corresponds with one of the telephone wires which is
inserted in the same circuit, while the other corresponds with the bell
system S, which is in communication with earth. It follows from this
arrangement, that when the right telephone presses its whole weight
on the support, the bar of the commutator is inclined on the lower
contact, and consequently the line is in direct communication with
the bell, so that the call can be made. When, on the other hand, the
telephone is removed from its support, the bar rests on the higher
contact, and the telephones are connected with the line.
Pressure on the sending push serves to call the corresponding station:
the connection of the line with the telephones is then broken, and it
is established with the battery of the sending station, which sends
its current through the bell of the corresponding station. In order
to obtain this double effect, the contact spring of the sending push
generally rests upon a contact fastened to a piece of wood shaped like
a joiner’s rule, which covers it in front, and below this spring there
is a second contact, which communicates with the positive pole of the
station battery. The other contact corresponds with the line wire,
and a connection takes place between the earth wire and the negative
pole of the station battery, so that the earth wire is common to three
circuits:
1st. To the telephone circuit. 2nd. To that of the bell system. 3rd. To
that of the local battery.
The second fork, which supports the telephone on the right, is fixed to
the board, and is independent of any electric current.
It is clear that this arrangement may be varied in a thousand ways, but
the model we have just described is the most practical.
_Edison’s System._--The problem becomes more complex in the case of
battery telephones, since the battery must be common to both systems,
and the induction coil must be inserted in two distinct circuits. Fig.
55 represents the model adopted in Mr. Edison’s telephone.
[Illustration: FIG. 55.]
In this arrangement, there is a small stand C on the mahogany board on
which the bases of the two telephones rest. The bell system S is worked
by an electro-magnetic speaker P, which serves, when a Morse key is
added to the system, for exchange of correspondence in the Morse code,
if there should be any defect in the telephones, or to put them in
working order. Above the speaker there is a commutator with a stopper D
to adapt the line for sending or receiving, with or without the bell;
and below the stand C the induction coil, destined to transform the
voltaic currents into induced currents, is arranged in a small closed
box E.
When the commutator is at reception, the line is in immediate
correspondence either with the speaker or with the receiving telephone,
according to the hole in which the stopper is inserted; when, on the
other hand, it is at sending, the line corresponds to the secondary
circuit of the induction coil. Under these conditions the action is
no longer automatic; but since this kind of telephone can only be
usefully employed for telegraphy, in which case those who work it are
acquainted with electric apparatus, there is no inconvenience in this
complication.
CALL-BELLS AND ALARUMS.
The call-bells applied to telegraphic service have been arranged in
different ways. When the vibrating bells are in use, like those of
which we have just spoken, it is necessary to use a battery, and
the advantages offered by telephones with induced currents are thus
sensibly diminished. In order to dispense with the battery, the use of
the electro-magnetic bell has been suggested.
In this case there are usually two bells, with a hammer oscillating
between them, and a support formed of the polarised armature of an
electro-magnet. The electro-magnetic instrument is placed below this
system; it is turned by a winch, and sends the currents, alternately
reversed, which are necessary to communicate the vibratory movement
to the hammer, and this movement is enough to make the two bells
tinkle. Below the winch of this electro-magnetic instrument there is a
commutator with two contacts, which adapts the instrument for sending
or receiving.
M. Mandroux has simplified this system, and has reduced it to small
dimensions by the following arrangement. He fixes two magnetic cores,
furnished with coils, on each of the two poles of a horseshoe magnet,
composed of two bars connected by an iron coupler, and between the
poles expanded by these four cores he inserts an armature, within
which there is a steel spring fastened to one of these poles. In this
way the armature is polarised, and oscillates under the influence of
the reversed currents transmitted by an instrument of the same kind
provided with an induction system. These oscillations may have the
effect of producing the sound of a call-bell, and the induction system
may consist of a manipulating key, fastened to a duplex system of
armature, regularly applied to the magnetic cores, taken in pairs. On
communicating a series of movements to this manipulator, a series of
induced currents in an inverse direction are produced, which cause the
armature of the corresponding station to act as we have already seen,
and which may even, when necessary, furnish a series of Morse signals
for a suitable manipulation. On account of the small size of this
system, it might be applied to the telephonic service of the army.
The Bell Telephone Company in Paris has arranged another little
call-system which is quite satisfactory and has the advantage of
acting as a telephone at the same time. The model resembles the one
we have termed a snuff-box telephone, and it has a button commutator
by means of which the instrument is placed in communication with the
electro-magnetic system of the instrument, or with a battery which is
able to make the telephone vibrate with some force. To make a call,
the button must be pressed, and the battery current is communicated
to the corresponding instrument, which begins to vibrate when the call
is made; and when notice is given of the receipt of the signal, the
pressure on the button is removed, and it becomes possible to speak and
receive as in ordinary telephones.
[Illustration: FIG. 56.]
_M. de Weinhold’s System._--M. Zetzche speaks highly of an alarum
devised by Professor A. de Weinhold, which resembles that by M. Lorenz,
represented in fig. 56. Its organ of sound consists of a steel bell T,
from 13 to 14 centimètres in diameter, and toned to give about 420
double vibrations in a second. ‘Its diameter and tone,’ he says, ‘are
important, and any great departure from the rule laid down diminishes
the effect. The opening of the bell is below, and it is fixed on a
stand by its centre. A slightly curved bar magnet, provided at its two
ends with iron appendices enclosed in a coil, traverses the stand.
The bar magnet of the telephone also terminates in an iron appendix
enclosed in a coil. In both cases the changes produced in the magnetic
condition appear to be more intense than they are in magnets without
appendices. The bar magnet is placed within the bell in the direction
of one of its diameters, so that the appendices almost touch its sides.
‘When the bell is struck on a spot about 90° from this diameter with
a wooden clapper M, which acts with a spring, and is withdrawn by
stretching the spring and then letting it go, as in a bell for the
dinner-table, the vibrations imparted to it send currents into the
coils, and these currents produce identical vibrations on the iron
disk of the telephone, which are intensified by a conical resonator
fitted to the telephone, so as to be easily heard some paces off. For
ordinary use, the bell coil is broken into a short circuit by means of
a metallic spring R, and consequently, when the bell is struck, the
spring must be opened so as not to break the circuit. An instrument of
the same kind has also been devised by Herr W. E. Fein at Stuttgardt.’
[Illustration: FIG. 57.]
[Illustration: FIG. 58.]
_MM. Dutertre and Gouault’s System._--One of the most ingenious
solutions of the problem of making the telephone call has recently been
proposed by MM. Dutertre and Gouault. Figs. 57 and 58 represent the
opposite faces of the instrument. It consists of a kind of snuff-box
telephone, like the one shown in fig. 26, and it is so arranged as to
send or receive the call, according to the way in which it is placed on
its stand, which is only an ordinary bracket fastened to the wall. When
it is placed on the bracket so as to have the telephone mouthpiece on
the outside, it is adapted for receiving, and can then give the call.
When, on the other hand, its position on the bracket is reversed, it
permits the other station to make the call, by producing vibrations
on a vibrator under the influence of a battery, and these vibrations
reverberate in the corresponding instrument with sufficient force to
produce the call. If the instrument is taken up, and the finger is
placed on a small spring button, it may then be used as an ordinary
telephone.
In this instrument, the magnet N S (fig. 57) is snail-shaped, like
others we have mentioned, but the core of soft iron S, to which the
coil E is fastened, can produce two different effects on its two
extremities. On the one side, it reacts on a small armature which is
fastened to the end of a vibrating disk C, fig. 58; the armature is
placed against a contact fastened to the bridge B, and constitutes an
electro-magnetic vibrator. For this purpose the bridge is in metallic
communication with the coil wire, of which the other end corresponds
with the line wire, and the spring C is mounted on an upright A, which
also supports another spring D G acting on two contacts, one placed at
G, and corresponding to the earth wire, the other at H, and connected
with the positive pole of the battery. A small moveable button, which
passes through a hole in the lid of the box, and projects beyond it, is
fixed at G, and all this part of the instrument faces the bottom of the
box. The upper part consists of the vibrating disk and the mouthpiece,
so that the mechanism we have described is all mounted on an inner
partition forming a false bottom to the box.
When the box rests upon its base, on the side shown in fig. 58, the
button at G presses on the spring D G, and raises it so as to break the
connection with the battery; the coil of the instrument is then united
to the circuit, and consequently receives the transmitted currents,
which follow this route: line wire, coil E, bridge B, spring C, spring
D G, earth contact. If these currents are transmitted by a vibrator,
they are strong enough to produce a noise which can be heard in all
parts of a room, and consequently the call may be given in this way.
If the currents are due to telephonic transmission, the instrument is
applied to the ear, care being taken to put the finger on the button
G, and the exchange of correspondence takes place as in ordinary
instruments; but it is simpler and more manageable to insert a second
telephone in the circuit for this purpose. When the box is inverted on
its mouthpiece, and the button G ceases to press on the spring D G, the
battery current reacts on the vibrator of the instrument, and sends the
call to the corresponding station, following this route: I D A C B E,
line, earth and battery; and the call goes on until the correspondent
breaks the current by taking up his instrument, thus warning the other
that he is ready to listen.
_System of M. Puluj._--There is yet another call system, devised
by M. Puluj. It consists of two telephones without mouthpieces,
connected together, and with coils placed opposite the branches of two
tuning-forks, tuned as nearly as possible to the same tone. A small
metal bell is fixed between the opposite faces of the tuning-forks, and
a wire stretched near them is provided with a small ball in contact
with their branches. When the tuning-fork at the sending station is put
in vibration by striking it with an iron hammer covered with skin, the
tuning fork at the other station vibrates also, and its ball strikes
upon the bell. As soon as the signal is returned by the second station,
mouthpieces with iron diaphragms are fastened to the telephones, and
the correspondence begins. It seems that, by the use of a resonator,
the sound which reaches the receiving station may be so intensified as
to become audible in a large hall, and the bell signal may be heard in
an adjoining room, even through a closed door.
_Mr. Alfred Chiddey’s System._--This arrangement consists of a slender
copper tube, eight inches long, and with an orifice of 1/30 of an inch,
of which the lower end is soldered to the diaphragm of a telephone. A
branch joint, to which an india-rubber tube is fitted, connects it with
a gas jet, which is lighted and surrounded with a lamp shade, in such
a way as to make it produce, under given conditions, sounds resembling
those of the singing flames. A perfectly similar system is arranged
at the other end of the line, in such a way that the sounds emitted
in each case shall be precisely in unison. If the two systems are so
regulated as not to emit sounds in their normal condition, they can
be made to sing by causing a tuning-fork in the vicinity of one or the
other to vibrate the same note, and then the corresponding flame will
begin to sing, producing a vibration in the diaphragm of the telephone
with which it is in correspondence, and hence will follow the vibration
of the diaphragm of the other telephone, and consequently the vibration
of the flame of the calling instrument. In this way the call signal may
be made without the intervention of any battery.
APPLICATIONS OF THE TELEPHONE.
The applications of the telephone are much more numerous than might
be supposed at the first glance. As far as the telegraphic service
is concerned, its use must evidently be rather limited, since it
cannot register the messages sent, and the speed of transmission is
inferior to that of the improved system of telegraphs; yet in many
cases it would be very valuable, even for a telegraphic system, since
it is possible to work it without any special telegraphic training.
The first comer may send and receive with the telephone, and this is
certainly not the case even with the simplest forms of telegraphic
instruments. This system is therefore already in use in public offices
and factories, for communication in mines, for submarine works, for
the navy, especially when several vessels manœuvre in the same
waters, some towed by others; finally, for military purposes, either
to transmit orders to different corps, or to communicate with schools
of artillery and rifle practice. In America the municipal telegraphic
service and that of telegraphs limited to the area of towns are
conducted in this way, and it is probable that this system will soon
be adopted in Europe. Indeed, a service of this kind was established
in Germany last autumn at the telegraph offices of some towns, and the
London Post Office is now thinking of establishing it in England.