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Page 28
* * * * *
TELEPHONIC TRANSMISSION WITHOUT RECEIVERS.
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.
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