The annual meeting of the French Society of Physics, the success of
which is continually increasing, took place this year in the salons of
the Observatory, which were kindly placed at the Society's disposal by
Admiral Mouchez.
There were three consecutive sessions, the one of Tuesday, April 15,
being set apart for the members of the Association, the one of the
16th for the invited guests of Admiral Mouchez, and that of the 17th
for the invited guests of the Society. The salons were partially
lighted by the Siemens differential arc, continuous current lamps, and
partially by the Swan incandescent lamp supplied by a distributing
machine that permitted of the lamps being lighted and extinguished at
will without changing the normal operation of all the rest. Many
apparatus figured at this exhibition, but we shall on the present
occasion merely call attention to those that presented a certain
character of novelty or of originality.
Among the apparatus that we shall reserve a description of for the
present was Messrs. Richard Bros.' registering thermometer designed
for the Concarneau laboratory, an instrument which, when sunk at one
mile from the coast, and to a depth of 40 meters, will give a diagram
of the temperature of the ocean at that depth; and Mr. Hospitalier's
continuous electrical indicators, designed for making known from a
distance such mechanical or physical phenomena as velocities, levels,
temperatures, pressures, etc.
Among the most important of the apparatus exhibited we must reckon Mr.
Cailletet's devices for liquefying gases, and those of Mr. Mascart for
determining the ohm. The results obtained by Mr. Mascart (which have
been submitted to the Committee on Unities of the Congress of
Electricians now in session at Paris), are sensibly concordant with
those obtained independently in England by Lord Rayleigh. Everything
leads to the hope, then, that a rapid and definite solution will be
given of this important question of electric unities, and that nothing
further will prevent the international development of the C.G.S.
system.
Mr. Jules Duboscq made a number of very successful projections, and we
particularly remarked the peculiar experiment made in conjunction with
Mr. Parinaud, that gave in projection two like spectra produced by the
same prism, and which, through superposition, were capable of
increasing the intensity of the colors, or, on the contrary, of
reconstituting white light.
Among the optical applications we may cite Mr. Leon Laurent's
apparatus for controlling plane, parallel, perpendicular, and oblique
surfaces, and magic mirrors obtained with an ordinary light; Mr. S.P.
Thompson's apparatus for demonstrating the propagation of
electro-magnetic waves in ether (according to Maxwell's theory), as
well as some new polarizing prisms; and a mode of lighting the
microscope (presented by Mr. Yvon), that was quite analogous to the
one employed more than a year ago by Dr. Van Heurck, director of the
Botanical Garden of Anvers.
Acoustics were represented by an electro-magnetic brake siren of Mr.
Bourbouze; Konig's apparatus for the synthesis of sounds; and Mr. S.P.
Thompson's cymatograph--a pendulum apparatus for demonstrating the
phenomena of beats.
It was electricity again that occupied the largest space in the
programme of the session.
Apparatus for teaching are assuming greater and greater importance
every day, and the exhibit of Mr. Ducretet included a large number of
the most interesting of these. The house of Breguet exhibited on a
reduced scale the magnificent experiments of Gaston Plante, wherein
320 leaden wire secondary elements charged for quantity with 3 Daniell
elements, and afterward coupled for tension, served to charge a
rheostatic machine formed of 50 condensers coupled for quantity. These
latter, coupled anew for tension, furnished upon being discharged a
spark due to a difference of potential of about 32,000 volts that
presented all the characters of the spark produced by induction coils
on the machines so improperly called "static." Finally, we may cite
the apparatus arranged by Mr. S.P. Thompson for studying the
development of currents in magneto-electric machines. The inventor
studies the influence of the forms of the inductors and armatures of
machines by means of an arrangement that allows him to change the
rings or armatures at will and to take out the induced bobbins in
order to sound every part of the magnetic field. Upon giving the
armature an angular motion limited by two stops, there develops a
certain quantity of electricity that may be measured by causing it to
traverse an appropriate ballistic galvanometer. Messrs. Deprez and
D'Arsonval's galvanometer answers very well for this purpose, and its
aperiodicity, which causes it quickly to return to zero as soon as the
induced current ceases, permits of a large number of readings being
taken within a very short space of time.
Measuring apparatus were represented by a new and very elegant
arrangement of Sir William Thomson's reflecting galvanometers, due to
Mr. J. Carpentier. The mounting adopted by Mr. Carpentier permits of
an easy removal of the bobbins and of an instantaneous substitution
therefor. The galvanometric part, composed of the needles and mirror,
therefore remains entirely free, thus allowing of its being verified,
and making it convenient to attach the silken fiber. Mr. Carpentier
has, moreover, adopted for all the minor apparatus a transparent
celluloid scale which simplifies them, facilitates observations, and
renders the use of reflection almost industrial.
We shall complete our enumeration of the measuring apparatus by citing
Ducretet's non-oscillating galvanometer, Sir William Thomson's
amperemeters, voltameters, ohmmeters, and mhosmeters, constructed and
exhibited by Breguet, and a new aperiodic galvanoscope of Mr. Maiche.
Mr. Baudot exhibited the recent improvements that he has made in his
multiplex printing telegraph, and M. Boudet of Paris showed a new
system of telephone transmission by submarine cables.
[Illustration: FIG. 1.--DIAGRAM EXHIBITING THE ARRANGEMENT FOR
TELEPHONIC TRANSMISSIONS WITHOUT A RECEIVER.]
Finally, we shall conclude our enumeration by referring to the
curiosities. The house of Siemens exhibited a miniature electric
railway actuated by a new model of Reynier accumulators; M. Maiche
operated a system of musical telephonic auditions that differed only
in detail from those instituted by Mr. Ader at the exhibition of 1881;
and Mr. Hospitalier presented a new form of an experiment devised by
Mr. Giltay, consisting of a telephonic transmission of sounds without
the use of receivers. Mr. Giltay's experiment is nothing but Mr.
Dunand's speaking condenser without the condenser. A glance at Fig. 1
will show how things are arranged for the experiment. The transmitting
system comprises two distinct circuits, viz.: (1) one formed of a
pile, P, of 2 or 3 Leclanche elements, or of 1 or 2 small sized
accumulators, an Ader microphane transmitter, M, and the inducting
wire of a small induction coil, B; and (2) the other formed of the
induced wire of the coil, B, of a pile, P', of 10 or 12 Leclanche
elements, and of a line whose extremities terminate at R, in two
ordinary electro-medical handles. With this arrangement the experiment
performed is as follows: When any one speaks or sings in front of the
transmitter, T, while two persons, A and B, each having one hand
gloved, are holding the handles in the ungloved hand, it is only
necessary for A to place his gloved hand upon B's ear, or for the
latter to place his hand upon A's, or for each to place his hand on
the other's ear simultaneously, in order that A or B, or A and B
simultaneously, may hear a voice issuing from the glove. Under these
circumstances, Mr. Giltay's experiment is explained like Dunand's
speaking condenser--the hand of A and the ear of B here constituting
the armature of an elementary condenser in which the glove performs
the role of dielectric.
Upon repeating this experiment at the laboratory of the School of
Physics and Industrial Chemistry of Paris, it has been found that the
glove maybe replaced by a sheet of plain or paraffined paper. In this
case, when two persons are holding the handles, and have their ears
applied, one against the other, if a sheet of paper be interposed,
airs or words will be heard to proceed therefrom. Finally, it has been
found possible to entirely suppress the paper, or dielectric, and to
hear directly, by simply interposing the auditor or auditors in the
circuit. One of the most curious forms of the experiment is the one
shown in Fig. 2. Here a third person, C, hears the hands of A and B
speak when a circuit is formed by means of three persons, A, B, and C,
the two former, A and B, each holding one of the wires of the circuit
and applying his free hand to the ear of C. Although the experiment is
one that requires entire silence, and could not on that account be
performed at the laboratory, a sort of telephonic chain can be formed
in which five or six persons may hear at the same time. A, putting his
hand on the ear of B, the latter putting his to that of C, and so on
up to the last person, who closes the circuit by grasping one of the
handles, the other one being held by A.
[Illustration: EXPERIMENT ON TELEPHONIC TRANSMISSION WITHOUT
RECEIVING APPARATUS.]
It is difficult in the present state of science to explain very
clearly how these telephonic transmissions are effected without a
receiver. All that we can conclude from it so far is that the ear is
an instrument of incomparable delicacy and of exquisite sensitiveness,
since it perceives vibrations in which the energy developer,
particularly in the telephonic chain, is exceedingly feeble.
Without any desire to seek an application for an experiment that is
simply curious, we yet believe that there is here a phenomenon of a
nature to be studied by physicists. Discoveries in telephony and
microphony have certainly opened up to science, as regards both theory
and practice, new horizons that still promise other surprises for the
future. But to return to the observatory: The success obtained by the
exhibition of the French Society of Physics shows that these reunions
respond to a genuine need--that of instructing in and popularizing
science. While warmly congratulating the organizers of these meetings,
we may express a wish that the good example set by the Society of
Physics may be followed by other societies. We are convinced in
advance that an equal success awaits them.--_La Nature._
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