n-volatile petroleum, known as thin machinery oil. The electromotive
force obtained varies with the temperature; a pile of 295 pairs having
a resistance of 95.6 ohms at 16 deg. Cent. gave with a difference of
temperature of 100 deg. Cent. an electromotive force of 0.7729 volts,
or with 130 deg. Cent. an electromotive force of 1.005 volt. Each
element, therefore, equaled 0.0000262 volt for each degree Cent.
difference of temperature. On having been verified with a standard
voltaic cell the apparatus becomes itself a standard, especially for
small electromotive forces. It is capable of measuring the 1/34861
part of a volt. For higher electromotive forces than a volt, several
of these piles would have to be connected in series. The fractional
electromotive force is obtained by means of a sliding contact which
cuts out so many pairs as is required.

* * * * *

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 exhibite