sent at once in this way, but Mr. Gray has only adapted his instrument
for four; he has, however, made use of the duplex system, which allows
him to double the number of transmissions, so that eight messages may
be sent at the same time, four in one direction, and four in another.
Mr. Hoskins asserts that this system has been worked with complete
success on the lines of the Western Union Telegraph Company, from
Boston to New York, and from Chicago to Milwaukee. Since these
experiments were made, fresh improvements have rendered it possible to
send a much larger number of messages.
Mr. Gray has also, aided by Mr. Hoskins, devised a system by which
telephonic messages may be sent on a wire previously used for Morse
instruments. Mr. Varley had already solved this problem, but Mr. Gray’s
system seems to have produced important results, and has therefore a
claim to our attention. We do not, however, describe it here, since it
is not within the lines marked out for us, and those who are interested
in the subject will find all the necessary details in a paper inserted
in the ‘Journal of the Society of Telegraphic Engineers, London,’ vol.
vi.
_Mr. Varley’s System._--This system is evidently the earliest in date,
since it was patented in 1870, and the patent describes the principle
of most of the arrangements which have since been adopted by Messrs.
Lacour, Gray, and Bell. It is based upon the use of his own musical
telephone, which we have already described, but with some variations in
its arrangement, which make it somewhat like the Reiss system.
It was Mr. Varley’s aim to make his telephone work in conjunction with
instruments with ordinary currents, by the addition of rapid electric
waves, incapable of making any practical change in the mechanical
or chemical capacity of the currents which serve for the ordinary
signals, yet able to make distinct signals, perceptible to the ear and
even to the eye. He says: ‘An electro-magnet offers at first a great
resistance to the passage of an electric current, and may consequently
be regarded as a partially opaque body with respect to the transmission
of very rapid inverse currents or of electric waves. Therefore, if a
tuning-fork, or an instrument with a vibrating plate, tuned to a given
note, be placed at the sending station, and so arranged as to be kept
in constant vibration by magnetic influence, the current which acts
upon it must be passed into two helices placed one above the other so
as to constitute the primary helix of an induction coil: in this way
it will be possible to obtain in two distinct circuits two series of
rapidly broken currents, which will correspond to the two directions of
the vibrations of the tuning-fork, and we shall also have the induced
currents produced in the secondary helix by these currents, which may
act on a third circuit. This third circuit may be placed in connection
with a telegraphic line previously used by an ordinary telegraphic
system, if a condenser is applied to it, and in this way two different
transmissions may be obtained simultaneously.’
[Illustration: FIG. 65.]
Fig. 65 represents the arrangement of this system. D is the vibrating
plate of the tuning-fork designed to produce the electric contacts
necessary to maintain it in motion. These contacts are at S and S′, and
the electro-magnets which affect it are at M and M′. The induction coil
is at I′, and the three helices of which it is composed are indicated
by the circular lines which surround it. There is a Morse manipulator
at A, another at A′, and the two batteries which work the system are at
P and P′. The condenser is at C, and the telephone is at the end of the
line L.
When the vibration of the plate D tends to the right, and the electric
contact takes place at S′, the current of the battery P′, after
traversing the primary helix, reaches the electro-magnets M M′, which
give it an impulse in the contrary direction. When, on the other hand,
it tends to the left, the current is sent through the second primary
circuit, which will be balanced by the first. Consequently there will
be a series of reversed currents in the induced circuit corresponding
to the key A′, which will alternately charge and discharge the
condenser C, thus sending into the line a corresponding series of
electric undulations which will react on the telephone placed at the
end of the line; and as the duration of the transmitted currents
will vary with the time that the key A′ is lowered, a correspondence
in the Morse code may be obtained in the telephone, while another
correspondence is exchanged with the key A and the ordinary Morse
receivers.
In order to render the vibratory signals visible, Mr. Varley proposes
to use a fine steel wire, stretched through a helix and facing a narrow
slit, to reproduce the vibrations. A light, which is intercepted by the
wire, is placed behind the slit. As soon as a current passes, the wire
vibrates and the light appears. A lens is placed so as to magnify the
image of the luminous slit, and project it on a white screen while the
wire is in vibration.
VARIOUS USES OF THE TELEPHONE.
_Its domestic application._--We have seen that telephones may be used
with advantage in public and private offices: they can be set up
at a much less expense than acoustic tubes, and in cases where the
latter would never be employed. With the aid of the calls we have
described, they offer the same advantages, and the connection between
the instruments is more easily concealed. The difference of price in
establishing them is in the ratio of one to seven.
For this purpose electro-magnetic telephones are evidently the best,
since they require no battery and are always ready to work. They are
already in use in many Government offices, and it is probable that they
will soon be combined with electric bells for the service of hotels and
of large public and private establishments: they may even be used in
private houses for giving orders to servants and porters, who may thus
save visitors from the fatigue of a useless ascent of several storeys.
In factories, telephones will certainly soon replace the telegraphic
communication which has already become general. They may not only be
used for ordinary messages, but to call for help in case of fire,
and they will become an integral part of several systems already
established for this purpose.
In countries which have free telegraphic communication, the telephone
has already replaced in great measure the private telegraph instruments
which have hitherto been in use; and if the same privilege is extended
to France, no other mode of correspondence will be used.
_Its application to telegraphic service._--The advantage to be derived
by the telegraphic service from the telephone is rather limited, since,
as far as the speed of transmission is concerned, it is of less value
than many of the telegraphic instruments now in use, and the messages
which it produces cannot be registered. Yet in municipal offices not
overburdened with messages they offer the advantage of not requiring a
trained service. On longer lines their use would be of little value.
The ‘Berne Telegraphic Journal’ has published some interesting remarks
on this subject, of which the following is a summary.
1st. In order to send a message with the special advantages of the
system, the sender ought to be able to address his correspondent
without the intervention of an official. Those who are acquainted with
the network of wires know this to be impossible. Intermediate offices
for receiving messages are essential, and the public cannot be admitted
to those set apart for sending and receiving; consequently the sender
must deliver a written message.
2nd. If the message is written, the chief advantage of the instrument
is lost, since it must be read and uttered aloud, which could not
be done if expressed in a language with which the employés were
unacquainted.
3rd. The instruments now in use at the telegraph offices can transmit
messages more quickly than if they were spoken.
In Germany, however, a telephone service has been established in
several telegraph offices, and its possible advantages are enumerated
as follows in the official circular which created it:
‘The offices which will be opened to the public for the service
of telephonic messages in Germany will be regarded as independent
establishments; yet they will be in connection with the ordinary
telegraph offices, which will undertake to send telephonic messages
through their wires.
‘The transmission will take place as follows: The sending office will
request the receiving office to prepare the instrument; as soon as
the tubes are adjusted, the sending office will give the signal for
despatching the verbal message.
‘The sender must speak slowly and clearly, without raising his voice;
each syllable must be distinctly pronounced; the final syllables
especially must be well articulated, and there must be a pause after
each word, in order to give the receiver time to write it down.
‘When the telegram has been received, the employé at the receiving
office must verify the number of words; then he must repeat through the
telephone the whole message without pausing, so as to make sure that
there is no mistake.
‘In order to ensure secrecy, the telephones are placed apart, where
persons unconnected with the service cannot hear the verbal message,
and the employés are forbidden to reveal to anyone the names of the
correspondents.
‘The charge for telephonic messages, as for the ordinary telegraphic
services, is at the rate of so much a word.’
The use of the telephone has also been suggested for verifying the
perfect junction of telegraphic wires. It is certain that, if the
junction is complete, no abnormal sounds will be heard, or only those
which result from accidental currents; but if the junction is bad, the
imperfect contacts which take place produce variations in electric
intensity which are translated into the more or less marked sounds
observed in the telephone.
M. Mauborgne, the electrician attached to the Northern Railway of
France, has lately used the telephone instead of the galvanometer to
ascertain the condition of the circuits in correspondence with the
instruments in use for electric signals. The reactions produced on
the galvanometer needle by the pieces of iron which are placed at the
sides of the railway often make its indications uncertain, and a strong
wind produces irregular movements in the instrument which interfere
with observations. It was also necessary to place the galvanometer
with due regard to the points of the compass, and to wait for the
needle to settle, which involved loss of time. The operation is easily
accomplished with the telephone, since the strokes of the call-bell are
distinctly reproduced; it is made to ring by working the contacts which
need verification, and in the same way the condition of the battery can
be ascertained.
_Application to military purposes._--Since the telephone was invented,
numerous experiments have been made in different countries to ascertain
whether it would be of use in military operations. These experiments
have hitherto been only moderately satisfactory, on account of the
noise inseparable from an army, which generally makes it impossible
to hear the telephone, and every means of intensifying its sounds has
been eagerly sought. It was at first supposed that the discovery of
the microphone had solved the problem, and I received many enquiries
from military schools on the subject, but I have not been able to see
that anything has been gained from this point of view. The telephone
is, however, of great use in schools of artillery and rifle practice.
Now that firearms carry so far, it has become necessary to be informed
by telegraph of the points hit on the target, in order to judge of
the accuracy of aim, and for this purpose telegraphic targets were
suggested; but telephones are much to be preferred, and they are now
used with good effect.
If the telephone is unsuited for the service of the flying telegraph in
the field, it may be of great use in the defence of towns, to transmit
the orders of the commandant to different batteries, and even for the
exchange of correspondence with captive balloons sent to hover over
fields of battle.
In spite of the difficulties attending its use, the experiment was
made by the Russians in the late war: the cable wire of communication
was 500 or 600 yards long, and so light that it could be laid by one
man. The ‘Telegraphic Journal’ of March 15, 1878, states that the bad
weather did not interfere with the working of the instruments; but the
noise made it difficult to hear, and it was necessary to cover the head
with a hood to intercept external sounds. This cannot be considered a
satisfactory result, yet the telephone may be of great service to an
army by intercepting the enemy’s messages: a bold man, provided with a
pocket telephone, who placed himself in a retired spot, might divert
the current of the enemy’s telegraphic wire into his telephone, and get
possession of all his despatches, as we saw was the case at Clermont.
He might even do this by diverting the current to earth or to a rail of
the railway line. These are suggestions for future research, and it is
probable that they may some day be turned to practical account.
_Its application to the navy._--The telephone may be of the greatest
use in naval matters, for the service of electro-semaphores, for
island forts and ships at anchor. M. Pollard says that ‘experiments
made between the Préfecture Maritime at Cherbourg, the semaphores and
the forts on the mole, demonstrate the advantage there would be in
establishing telephones at these stations, since they would ensure an
easy communication between the vessels of a squadron and the land they
are approaching. By sinking small cables which come to the surface
of the water along mooring chains, and terminate in buoys or cases
which remain permanently in the harbour, the ships of war may in this
way place themselves in communication with the Préfecture Maritime as
they cast anchor, and, by temporarily connecting the vessels together
with light cables, the admiral may communicate freely with the whole
squadron.’
The telephone has been tried on board ship for transmitting orders, but
without success, on account of the noise always going on in a vessel.
The telephone may be usefully applied to the service of submarine
torpedoes. We have already seen how it may be applied in connection
with the microphone, but it may also be used in firing the torpedoes
after the exact position of the enemy’s ship has been ascertained from
two reconnaissances taken from different parts of the coast.
The telephone, again, makes it possible to verify the condition of
torpedoes, and to ascertain if there is any fault in the circuit within
the explosives. For this purpose a very weak current has been used,
and a galvanometer is not always able to indicate the fault, while the
extreme sensitiveness of the telephone will do so in the simplest way.
Captain M’Evoy, of the American Army, suggested a way of ascertaining,
while on shore, the condition of torpedoes under water, by connecting
the buoys which support them with the land by means of a telephonic
line. By inserting, in the buoy which supports the torpedo, metallic
disks, so arranged as to vibrate with every movement caused by the
waves upon the buoy, a continuous noise will be heard in the telephone,
after the circuit has been completed by the metallic disks; and the
noise will go on as long as the disks continue to oscillate, and will
cease as soon as the buoy is completely covered by the water. When it
ceases, therefore, if not affected by some accidental cause, it may be
supposed that the enemy’s ship is passing over the buoy.
M. Trève, again, has shown that the telephone might be used with
advantage for the telegraphic communication between vessels in tow, and
M. des Portes has applied it with good effect to diving operations. In
this instance, one of the glass panes in the helmet is replaced by a
copper plate in which the telephone is framed, so that the diver need
only make a slight movement of his head in order to receive or address
communications to those in charge of the apparatus. With this system
the keels of vessels may be examined, and an account given of their
condition, without bringing up the divers, which has hitherto been
necessary.
M. de Parville, the able and learned editor of the _Journal
Scientifique_ and the science department of the _Journal des Débats_,
has suggested a new and interesting application of the telephone. It
concerns the possibility of making use of it to determine the precise
position of the magnetic meridian, that is, the true direction of the
magnetised needle.
For this purpose a Bell telephone is necessary, of which the
magnetic core is formed of an iron rod a mètre in length, kept, by
a suitable suspension, at nearly the same angle of inclination as a
dipping-needle. This rod will be magnetised under the influence of
terrestrial magnetism, and the telephone will be able to transmit
the sounds produced by some sort of vibrator placed near its
mouthpiece. These sounds will be strong in proportion to the degree
of magnetisation of the bar; and if the telephone is turned round the
horizon, keeping the bar at the same angle of inclination, the sounds
transmitted to the receiving telephone will be greatest when the axis
of the bar is in the plane of the magnetic meridian, and least when
it is at 90°. It will therefore be possible to ascertain from the
direction of the axis at the moment when the sounds are no longer
heard, the exact inclination of the magnetic needle from north to
south, for it will be given by the perpendicular to the line which is
followed by the axis of the iron bar at that moment.
It is possible that, with this system, the disturbing influence on the
magnetic needle of the mass of iron in iron-plated vessels might be
almost destroyed, and a more exact orientation than that of the compass
might be obtained. The same process may make it possible to estimate
and measure the variations of terrestrial magnetism. M. de Parville has
not himself tried to apply this system; but Mr. Blake’s experiments, of
which we spoke in an early part of this work, make it probable that it
might be done with advantage.
_Application to industry._--One of the earliest and most important
applications of the telephone is that which was first made to the
service of mines in England and America in the autumn of 1877. The
great length of the galleries is well known, and had already involved
the use of the electric telegraph for transmitting orders; but the
miners did not understand how to work these instruments, and the
service was ill performed. Thanks to the telephone, through which the
first corner can send and receive a message, there is no longer any
difficulty in the communication between the galleries and the surface
of the mine.
The ventilation of mines can also be regulated by the aid of
telephones. If one of these instruments is placed near a wheel kept
in motion by the air which passes through the ventilating shaft, and
another is placed in the inspector’s office he can ascertain by the
sound if the ventilation is duly carried on, and if the machine works
regularly.
_Application to scientific research._--M. d’Arsonval’s experiments,
which we have already mentioned, show that the telephone can be used
as an extremely sensitive galvanoscope; but since it can only produce
sounds under the influence of broken currents, the circuit on which the
experiment is made must be divided at rather close intervals. It has
been seen that it is not even necessary to insert the telephone in the
circuit: it may be influenced, when at a distance, either immediately
or by the induction of the broken current on a circuit placed parallel
to the first, and the force of these effects may be increased by the
reaction of a core of iron, round which the inducing circuit is wound.
The drawback to this system is that the direction of the current is
not ascertained, so that it cannot be used as a measuring instrument;
but, on the other hand, it is so sensitive, so easy to arrange, and so
inexpensive, that it might be of the greatest use as a galvanoscope.
Mr. Warren de La Rue has also made use of the telephone in his
researches into the electric discharges of high-tension batteries,
in order to follow the different phases of the discharge during the
luminous phenomena which it produces. In this way he ascertained
that when a condenser is placed in connection with a battery formed
of a considerable number of insulated elements, and is gradually
discharged through a Geissler tube, a dull and faint sound is heard
in the telephone, as long as the stratifications of light appear to
be perfectly stable; but the sound becomes considerably stronger,
and sometimes even piercing, in proportion to the diffusion of these
stratifications, and to their approach to the point of extinction:
whence it is shown that the discharge of a battery into tubes in which
a vacuum has been made is intermittent.
Mr. Spottiswoode has repeated the same experiments with the discharges
of Holtz machines, and with large condensers, and he found that the
most piercing sounds produced by the telephone coincided with the
greatest development of the stratifications. These sounds, however,
sometimes ceased for a moment. It was even possible to ascertain,
from the intensity of the sounds produced, the differences of tension
which might be manifested in the charge of the condenser and the
slackening of the machine’s motion, and the differences of intensity
in these sounds might in some cases exceed an octave. The fall in the
scale generally appeared in half-tones instead of gradually, and the
introduction of resistances into the circuit modified the sounds very
much: they might even be intensified by approaching the finger to the
discharging tube.
From experiments made with the telephone between Calais and Boulogne,
it appears that this instrument might be applied with advantage to the
science of projectiles. In fact, in some artillery practice which took
place on the shore at Boulogne, a telephone was placed close to the
gun, and the explosion was heard at a distance of nearly two miles,
where the projectile fell. It was possible to estimate its velocity by
measuring the lapse of time between the moment when the projectile left
the gun, and its fall. This calculation is usually made by observing
the flash from the cannon’s mouth; but in some cases, as in a fog or in
practice at long ranges, the telephone may be usefully substituted for
ocular observation. On the field of battle, an observer, provided with
a telephone and placed on a hill, might rectify from a distance the aim
of his battery, which is generally established in a sheltered and less
elevated place.
THE PHONOGRAPH.