of a
single tap, is very simple. When the mercury is raised, the tap is turned
in such a manner that the surplus of the liquid can pass into the enlarged
appendage, a, placed above the tap, and communication is then cut off by
turning the tap to 90 degrees.

The mercury reservoir having descended, the bulb empties itself, and then
the tap is turned on again, in order to establish communication with the
exhausting tube. The tap is then closed, the mercury ascends again, and
this action keeps on repeating.

[Illustration]

* * * * *

NO ELECTRICITY FROM THE CONDENSATION OF VAPOR.--It has been maintained by
Palmieri and others that the condensation of vapor results in the
production of an electrical charge. Herr S. Kalischer has renewed his
investigations upon this point, and believes that he has proved that no
electricity results from such condensation. Atmospheric vapor was condensed
upon a vessel coated with tin foil, filled with ice, carefully insulated,
and connected with a very sensitive electrometer. No evidence could be
obtained of electricity.--_Ann. der Physik und Chemie_.

* * * * *

THE ELECTRO-MAGNETIC TELEPHONE TRANSMITTER.

An interesting contribution was made by M. Mercadier in a recent number of
the _Comptes Rendus de l'Academie Francaise_. On the ground of some novel
and some already accepted experimental evidence, M. Mercadier holds that
the mechanism by virtue of which the telephonic diaphragms execute their
movements is analogous to, if not identical with, that by which solid
bodies of any form, a wall for instance, transmit to one of their surfaces
all the vibratory movements of any kind which are produced in the air in
contact with the other surface. It is a phenomenon or resonance. Movements
corresponding to particular sounds may be superposed in slender diaphragms,
but this superposition must necessarily be disturbing under all but
exceptional circumstances. In proof of this view, it is cited that
diaphragms much too rigid, or charged with irregularly distributed masses
over the surface, or pierced with holes, or otherwise evidently unfitted
for the purpose, are available for transmission. They will likewise serve
when feathers, wool, wood, metals, mica, and other substances to the
thickness of four inches are placed between the diaphragm and the source of
vibratory movement. The magnetic field does not alter these relati