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ELECTRICAL APPARATUS FOR MEASURING AND FOR DEMONSTRATION AT THE MUNICH
EXHIBITION.
Apparatus for use in laboratories and cabinets of physics were quite
numerous at the Munich Exhibition of Electricity, and very naturally a
large number was to be seen there that presented little difference
with present models. Several of them, however, merit citation. Among
the galvanometers, we remarked an apparatus that was exhibited by
Prof. Zenger, of Prague. The construction of this reminded us of that
of other galvanometers, but it was interesting in that its inventor
had combined in it a series of arrangements that permitted of varying
its sensitiveness within very wide limits. This apparatus, which Prof.
Zenger calls a "Universal Rheometer" (Fig. 1), consists of a bobbin
whose interior is formed of a piece of copper, whose edges do not
meet, and which is connected by strips of copper with two terminals.
This internal shell is capable of serving for currents of quantity,
and, when the two terminals are united by a wire, it may serve as a
deadener. Above this copper shell there are two identical coils of
wire which may, according to circumstances, be coupled in tension or
in series, or be employed differentially. Reading is performed either
by the aid of a needle moving over a dial, or by means of a mirror,
which is not shown in the figure. Finally, there is a lateral scale,
R, which carries a magnetized bar, A, that may be slid toward the
galvanometer. This magnet is capable of rendering the needle less
sensitive or of making it astatic. In order to facilitate this
operation, the magnet carries at its extremity a tube which contains a
bar of soft iron that may be moved slightly so as to vary the length
of the magnet. Prof. Zenger calls this arrangement a magnetic vernier.
It will be seen that, upon combining all the elements of the
apparatus, we can obtain very different combinations; and, according
to the inventor, his rheometer is a substitute for a dozen
galvanometers of various degrees of sensitiveness, and permits of
measuring currents of from 20 amperes down to 1/50000000 an ampere.
The apparatus may even be employed for measuring magnetic forces, as
it constitutes a very sensitive magnetometer.
[Illustration: FIG. 1.--ZENGER'S UNIVERSAL RHEOMETER.]
Prof. Zenger likewise had on exhibition a "Universal Electrometer"
(Fig. 2), in which the fine wire that served as an electrometric
needle was of magnetized steel suspended by a cotton thread. In this
instrument, a silver wire, t, terminating in a ball, is fixed to a
support, C, hanging from a brass disk, P, placed upon the glass case
of the apparatus. It will be seen that if we bring an electrified body
near the disk, P, a deviation of the needle will occur. The
sensitiveness of the latter may be regulated by a magnetic system like
that of the galvanometer. Finally, a disk, P', which may be slid up
and down its support, permits of the instrument being used as a
condensing electrometer, by giving it, according to the distance of
the disks, different degrees of sensitiveness. One constructor who
furnished much to this part of the exhibition was Mr. Th. Edelmann of
Munich, whose apparatus are represented in a group in Fig. 3. Among
them we remark the following: A quadrant electrometer (Fig. 4), in
which the horizontal 8-shaped needle is replaced by two connected
cylindrical surfaces that move in a cylinder formed of four parts; a
Von Beetz commutator; spyglasses with scale for reading measuring
instruments (Fig. 3); apparatus for the study of magnetic variations,
of Lamont (Fig. 3) and of Wild (Fig. 5); different types of the
Wiedemann galvanometer; an electrometer for atmospheric observations
(Fig. 6); a dropping apparatus (Fig. 7), in which the iron ball opens
one current at a time at the moment it leaves the electro-magnet and
when it reaches the foot of the support, these two breakages producing
two induction sparks that exactly limit the length to be taken in
order to measure the time upon the tracing of the chronoscope
tuning-fork; an absolute galvanometer; a bifilar galvanometer (Fig. 8)
for absolute measurements, in which the helix is carried by two
vertical steel wires stretched from o to u, and which is rendered
complete by a mirror for the reading, and a second and fixed helix, so
that an electro-dynamometer may be made of it; and, finally, a
galvanometer for strong currents, having a horseshoe magnet pivoted
upon a vertically divided column which is traversed by the current,
and a plug that may be arranged at different heights between the two
parts of the column so as to render the apparatus more sensitive (Fig.
9).
[Illustration: FIG. 2.--ZENGER'S UNIVERSAL ELECTROMETER.]
We may likewise cite the exhibit of Mr. Eugene Hartmann of Wurtzburg,
which comprised a series of apparatus of the same class as those that
we have just enumerated--spyglasses for the reading of apparatus,
galvanometers, magnetometers, etc.
[Illustration: FIG. 3.--EXHIBIT OF TH. EDELMANN.]
Specially worthy of remark were the apparatus of Mr. Kohlrausch for
measuring resistances by means of induction currents, and a whole
series of accessory instruments.
Among the objects shown by other exhibitors must be mentioned Prof.
Von Waltenhofen's differential electromagnetic balance. In this, two
iron cylinders are suspended from the extremities of a balance. One of
them is of solid iron, and the other is of thin sheet iron and of
larger diameter and is balanced by an additional weight. Both of them
enter, up to their center, two solenoids. If a strong current be
passed into these latter, the solid cylinder will be attracted; but
if, on the contrary, the current be weak, the hollow cylinder will be
attracted. If the change in the current's intensity occur gradually,
there will be a moment in which the cylinders will remain in
equilibrium.
[Illustration: FIG. 4.--EDELMANN'S QUADRANT ELECTROMETER.]
Prof. Zenger's differential photometer that we shall finally cite is
an improvement upon Bunsen's. In the latter the position of the
observer's eye not being fixed, the aspect of the spot changes
accordingly, and errors are liable to result therefrom. Besides,
because of the non-parallelism of the luminous rays, each of the two
surfaces is not lighted equally, and hence again there may occur
divergences. In order to avoid such inconveniences, Prof. Zenger gives
his apparatus (Fig. 10) the following form: The screen, D, is
contained in a cubical box capable of receiving, through apertures,
light from sources placed upon the two rules, R and R'. A flaring
tube, P, fixes the position of the eye very definitely. As for the
screen, this is painted with black varnish, and three vertical
windows, about an inch apart, are left in white upon its paper. Over
one of the halves of these parts a solution of stearine is passed. To
operate with the apparatus, in comparing two lights, the central spot
is first brought to invisibility, and the distances of the sources are
measured. A second determination is at once made by causing one of the
two other spots to disappear, and the mean of the two results is then
taken. As, at a maximum, there is a difference corresponding to 3/100
of a candle between the illumination of the two neighboring windows,
in the given conditions of the apparatus, the error is thus limited to
a half of this value, or 2 per cent. of that of one candle.
[Illustration: FIG. 5.--WILD'S APPARATUS FOR STUDYING MAGNETIC
VARIATIONS.]
Among the apparatus designed for demonstration in lecture courses, we
remarked a solenoid of Prof. Von Beetz for demonstrating the
constitution of magnets (Fig. 11), and in which eight magnetized
needles, carrying mica disks painted half white and half black, move
under the influence of the currents that are traversing the solenoid,
or of magnets that are bought near to it externally. Another apparatus
of the same inventor is the lecture-course galvanometer (Fig. 3), in
which the horizontal needle bends back vertically over the external
surface of a cylinder that carries divisions that are plainly visible
to spectators at a distance.
[Illustration: FIG. 6.--ELECTROMETER FOR ATMOSPHERIC OBSERVATIONS.]
Finally, let us cite an instrument designed for demonstrating the
principle of the Gramme machine. A circular magnet, AA', is inserted
into a bobbin, B, divided into two parts, and moves under the
influence of a disk, L, actuated by a winch, M. This system permits of
studying the currents developed in each portion of the bobbin during
the revolution of the ring (Fig. 12).
[Illustration: FIG. 7.--WIEDEMANN'S CURRENT BREAKER.]
To end our review of the scientific apparatus at the exhibition we
shall merely mention Mr. Van Rysselberghe's registering
thermometrograph (shown in Figs. 13 and 14), and shall then say a few
words concerning two types of registering apparatus--Mr. Harlacher's
water-current register and Prof. Von Beetz's chronograph.
[Illustration: FIG. 8.--WIEDEMANN'S BIFILAR GALVANOMETER.]
Mr. Harlacher's apparatus was devised by him for studying the deep
currents of the Elbe. It is carried (Fig. 15) by a long, vertical,
hollow rod which is plunged into the river. A cord that passes over a
pulley, P, allows of the apparatus, properly so called, being let down
to a certain depth in the water. What is registered is the velocity of
the vanes that are set in action by the current, and to effect such
registry each revolution of the helix produces in the box, C, an
electric contact that closes the circuit in the cable, F, attached to
the terminals, B. This cable forms part of a circuit that includes a
pile and a registering apparatus that is seen at L, outside of the box
in which it is usually inclosed. In certain cases, a bell whose sound
indicates the velocity of the current to the ear is substituted for
the registering apparatus.
[Illustration: FIG. 9.--WIEDEMANN'S GALVANOMETER FOR STRONG CURRENTS.]
Fig. 16 represents another type of the same apparatus in which the
mechanism of the contact is uncovered. The supporting rod is likewise
in this type utilized as a current conductor.
[Illustration: FIG. 10.--ZENGER'S DIFFERENTIAL PHOTOMETER.]
It now remains to say a few words about Prof. Von Beetz's chronograph.
This instrument (Fig. 17) is designed for determining the duration of
combustion of different powders, the velocity of projectiles, etc. The
registering drum, T, is revolved by hand through a winch, L, and the
time is inscribed thereon by an electric tuning fork, S, set in motion
by the large electro-magnet, E F. Each undulation of the curves
corresponds to a hundredth of a second. The tuning-fork and the
registering electro-magnets, G and H, are placed upon a regulatable
support, C, by means of which they may be given any position desired.
[Illustration: FIG. 11.--VON BEETZ'S SOLENOID FOR DEMONSTRATING THE
CONSTITUTION OF MAGNETS.]
The style, c, of the magnet, C, traces a point every second in order
to facilitate the reading. The style, b, of the electro-magnet, H,
registers the beginning and end of the phenomena that are being
studied.
[Illustration: FIG. 12.--APPARATUS FOR DEMONSTRATING THE PRINCIPLE OF
THE GRAMME MACHINE.]
The apparatus is arranged in such a way that indications may thus be
obtained upon the drum by means of induction sparks jumping between
the style and the surface of the cylinder. To the left of the figure
is seen the apparatus constructed by Lieutenant Ziegler for
experimenting on the duration of combustion of bomb fuses.
[Illustration: FIG. 13.--VAN RYSSELBERGHE'S REGISTERING
THERMOMETROGRAPH.]
Shortly after the drum has commenced revolving, the contact, K, opens
a current which supports the heavy armature, P, of an electro-magnet,
M. This weight, P, falls upon the rod, d, and inflames the fuse, Z, at
that very instant. At this precise moment the electro-magnet, H,
inscribes a point, and renews it only when the cartridge at the
extremity of the fuse explodes.
[Illustration: FIG. 14.--VAN RYSSELBERGHE'S REGISTERING
THERMOMETROGRAPH.]
This apparatus perhaps offers the inconvenience that the drum must be
revolved by hand, and it would certainly be more convenient could it
be put in movement at different velocities by means of a clockwork
movement that would merely have to be thrown into gear at the desired
moment. As it is, however, it presents valuable qualities, and,
although it has already been employed in Germany for some time, it
will be called upon to render still more extensive services.
[Illustration: FIG. 15.--HARLACHER'S APPARATUS FOR STUDYING DEEP
CURRENTS IN RIVERS.]
We have now exhausted the subject of the apparatus of precision that
were comprised in the Munich Exhibition. In general, it may be said
that this class of instruments was very well represented there as
regards numbers, and, on another hand, the manufacturers are to be
congratulated for the care bestowed on their construction.--_La
Lumiere Electrique_.
[Illustration: FIG. 16.--HARLACHER'S APPARATUS FOR STUDYING DEEP
CURRENTS IN RIVERS.]
[Illustration: FIG. 17.--VON BEETZ'S CHRONOGRAPH.]
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