d 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 characte