This apparatus has recently been the object of some experiments which
resulted in its being finally adopted in the army. We think that our
readers will read a description of it with interest. Its mode of
construction is based upon a theoretic conception of the lines of force,
which its inventor explains as follows in his Elementary Treatise on
Electricity:
"To every position of the disk of a magnetic telephone with respect to
the poles of the magnet there corresponds a certain distribution of the
lines of force, which latter shift themselves when the disk is
vibrating. If the bobbin be met by these lines in motion, there will
develop in its wire a difference of potential that, according to
Faraday's law, will be proportional to their number. All things equal,
then, a telephone transmitter will be so much the more potent in
proportion as the lines set in motion by the vibrations of the disk and
meeting the bobbin wire are greater in number. In like manner, a
receiver will be so much the more potent in proportion as the lines of
force, set in motion by variations in the induced currents that are
traversing the bobbin and meeting the disk, are more numerous. It will
consequently be seen that, generally speaking, it is well to send as
large a number of lines of force as possible through the bobbin."
[Illustration: FIG. 1.--THE COLSON TELEPHONE.]
In order to obtain such a result, the thin tin-plate disk has to be
placed between the two poles of the magnet. The pole that carries the
fine wire bobbin acts at one side and in the center of the disk, while
the other is expanded at the extremity and acts upon the edge and the
other side. This pole is separated from the disk by a copper washer, and
the disk is thus wholly immersed in the magnetic field, and is traversed
by the lines of force radiatingly.
This telephone is being constructed by Mr. De Branville, with the
greatest care, in the form of a transmitter (Fig. 2) and receiver (Fig.
3). At A may be seen the magnet with its central pole, P, and its
eccentric one, P'. This latter traverses the vibrating disk, M, through
a rubber-lined aperture and connects with the soft iron ring, F, that
forms the polar expansion. These pieces are inclosed in a nickelized
copper box provided with a screw cap, C. The resistance of both the
receiver and transmitter bobbin is 200 ohms.
[Illustration: FIG. 2.--TRANSMITTER TAKEN APART.]
The transmitter is 3½ in. in diameter, and is provided with a
re-enforcing mouthpiece. It is regulated by means of a screw which is
fixed in the bottom of the box, and which permits of varying the
distance between the disk and the core that forms the central pole of
the magnet. The regulation, when once effected, lasts indefinitely. The
regulation of the receiver, which is but 2¼ in. in diameter, is
performed once for all by the manufacturer. One of the advantages of
this telephone is that its regulation is permanent. Besides this, it
possesses remarkable power and clearness, and is accompanied with no
snuffling sounds, a fact doubtless owing to all the molecules of the
disk being immersed in the magnetic field, and to the actions of the two
poles occurring concentrically with the disk. As we have above said,
this apparatus is beginning to be appreciated, and has already been the
object of several applications in the army. The transmitter is used by
the artillery service in the organization of observatories from which to
watch firing, and the receiver is added to the apparatus pertaining to
military telegraphy. The two small receivers are held to the lens of the
operator by the latter's hat strap, while the transmitter is suspended
in a case supported by straps, with the mouthpieces near the face (Fig.
1).
In the figure, the case is represented as open, so as to show the
transmitter. The empty compartment below is designed for the reception
and carriage of the receivers, straps, and flexible cords. This
arrangement permits of calling without the aid of special apparatus, and
it has also the advantage of giving entire freedom to the man on
observation, this being something that is indispensable in a large
number of cases.
[Illustration: FIG. 3.--RECEIVER TAKEN APART.]
In certain applications, of course, the receivers may be combined with a
microphone; yet on an aerial as well as on a subterranean line the
transmitter produces effects which, as regards intensity and clearness,
are comparable with those of a pile transmitter.
Stations wholly magnetic may be established by adding to the transmitter
and two receivers a Sieur phonic call, which will actuate them
powerfully, and cause them to produce a noise loud enough for a call. It
would be interesting to try this telephone on a city line, and to a
great distance on those telegraph lines that are provided with the Van
Rysselberghe system. Excellent results would certainly be obtained, for,
as we have recently been enabled to ascertain, the voice has a
remarkable intensity in this telephone, while at the same time perfectly
preserving its quality.--_La Nature_.
* * * * *
[NATURE.]