Mr. F. Von Faund-Szyll has devised an original system of submarine
telegraph, which is based upon the well known property that selenium
exhibits of modifying its resistance under the influence of luminous
rays, and which he styles the _Selen-Differenzialrecorder_.
Contrary to what is found in the other systems hitherto employed, the
Faund-Szyll system utilizes the cable current merely for starting the
receiving apparatus, which are operated by means of strong local
batteries. The result is that the mechanical work that devolves upon
the line current, which is, as well known, very weak, is exceedingly
reduced.
The system consists of two essential parts: (1) The receiver, properly
so called. (2) The relay as well as the registering apparatus or
_differenzialrecorder_. The receiver consists of a closed box, K, in
the interior of which there is a very intense source of light whose
rays escape by passing through apertures, _a a'_, in the front part
(Fig. 1).
As a source of light, there may be conveniently employed an
incandescent lamp, _g_, capable of giving an intense light, and
arranged (as shown in Fig. 2) behind the side that contains the slits,
_a a'_.
The starting apparatus consists of a small galvanometric helix, _r_,
analogous to Thomson's siphon recorder, which is suspended from a
cocoon fiber and capable of moving in an extremely powerful magnetic
field, N S. This helix carries, as may be seen in Figs. 1, 3 and 4, a
prolongation, _v_, at its lower end whose form is that of a prism, and
which is arranged in front of the partition of the box, K, in such a
way that it exactly covers the two slits, a and _a_ when the bobbin is
at rest, and in this case prevents the luminous rays of the lamp, _g_,
from escaping from the box. But, as soon as the current sent through
the cable reaches the spirals of the bobbin, through the conductors,
_y y'_, the sum of the elementary electrodynamic actions that arise
causes the helix to revolve to the right or left, according to the
polarity of the current, while at the same time the helix slightly
approaches one or the other of the poles of the magnet. The
prolongation, _v_, of the helix, being firmly united with the latter,
follows it in its motion, and has the effect of permitting the
luminous rays to escape through one or the other of the slits, _a a'_,
so that the freeing of the luminous fascicle, if such an expression is
allowable, is effected.
[Illustration: FIG. 1.]
In order to prevent oscillations, which could not fail to occur after
each emission of a current (so that the helix, instead of returning to
a position of equilibrium and stopping there, would go beyond it and
alternately uncover the slits, _a a'_), the apparatus is provided with
a liquid deadener. To this end, the prolongation, _v_, carries a
piece, _o_, which dips into a cup containing a mixture of glycerine
and water.
We shall now describe the _differenzialrecorder_. Opposite the two
slits, _a_ and _a'_, there are two powerful converging lenses, _l_ and
_l'_, whose foci coincide with two sorts of selenium plate rheostat,
_z_ and _z'_. The result of this arrangement is that as soon as one of
the slits, as a consequence of the displacement of the helix, _r_,
allows a luminous fascicle to escape, this latter falls upon the
corresponding lens, which concentrates it and sends it to the selenium
plates just mentioned. Under the influence of the luminous rays, the
resistance that the selenium offers to the passage of an electric
current instantly changes. At M and M' are placed two horseshoe
magnets whose poles are provided with pieces of soft iron that serve
as cores to exceedingly fine wire bobbins, _d_. These polarized pieces
are arranged in the shape of a St. Andrew's cross, and in such a way
that the poles of the same name occupy the two extremities of the same
arm of the cross, an arrangement very clearly shown in Fig. 2.
[Illustration: FIG. 2.]
Between the poles of the magnets, M and M', there is a permanent
magnet, A, movable around a vertical axis, _i_. Four spiral springs,
_f_, whose tension may be regulated, permit of centering this latter
piece in such a way that when the current is traversing the spirals of
the polar bobbins it is equally distant from the four poles, _n_, _s_,
_s'_, and _n'_. Under such circumstances it is evident that a
difference in the power of attraction of these four poles, however
feeble it be, will result in moving the magnet, A, in one direction or
the other around its axis. The energy and extent of such motion may,
moreover, be magnified by properly acting upon the four regulating
springs.
The bobbins of the magnet, M, are mounted in series with the selenium
plates, _z_, the local battery, B, and a resistance box, W. Those of
the magnet, M', are in series with _z'_, B', and W'. The local
batteries, B and B', are composed of quite a large number of elements.
The current from the battery, B, traverses the selenium plates and the
bobbins of the magnet, M, and returns to B through the rheostat, W;
and the same occurs with the current from B'. The two currents, then,
are absolutely independent of one another.
From this description it is very easy to see how the system works. Let
us suppose, in fact, that the current which is traversing the spirals
of the helix, _r_, has a direction such that the helix in its movement
approaches the pole, S; then the prolongation, _v_, will uncover the
slit, _a_, which, along with _a'_, had up to this moment been closed,
and a luminous fascicle escaping through _a_ will strike the lens,
_l'_, and from thence converge upon the selenium plates, _z'_. This is
all the duty that the line current has to perform.
The luminous rays, in falling upon the selenium plates, _z'_, modify
the resistance that these offered to the passage of the current
produced by the battery, B'. As this resistance diminishes, the
intensity of the current in the circuit supplied by the battery, B',
increases, the attractive action of the polar pieces of the magnet,
M', diminishes, the equilibrium is destroyed, and the piece, A,
revolves around the axis, _i_. If the polarity of the line current
were different, the same succession of phenomena would occur, save
that the direction of A's rotation would be contrary. As for the
rheostats, W W', their object is to correct variations in the
selenium's resistance and to balance the resistances of the two
corresponding circuits. The magnet, A, will be combined with a
registering apparatus so as to directly or indirectly actuate the
printing lever. The entire first part of this apparatus, which is very
sensitive, may be easily protected from all external influence by
placing it in a box, and, if need be, in a room distant from the one
in which the employes work.
[Illustration: FIGS. 3 AND 4.]
The _differenzialrecorder_ alone has to be in the work room.
As may be seen, the system is not wanting in originality. Experience
alone will permit of pronouncing upon the question as to whether it is
as practical as ingenious.--_La Lumiere Electrique._
* * * * *