connected to the secondry circuit of the induction coil. This device
possesses the advantage that the electro-magnet can be powerfully
magnetized with very little battery power, no matter how long the line
may be, and that steel magnets are entirely dispensed with. It is not
necessary to have a separate battery for this purpose, as the microphone
battery may also be used for the telephone receiver. The shape of the
vibrating electro-magnets is immaterial, as they may be made of a
variety of forms.--_Eng. Mechanic_.

[Illustration: FIG. 1. FIG. 2]

* * * * *




ON AN ELECTRIC POWER HAMMER.

By MARCEL DEPREZ.

[Footnote: _La Lumiere Electrique_.]


In a lecture delivered by me on the 15th of last June in the
amphitheater of the Conservatoire des Arts et Metiers, on the
application of electricity to the production, transmission, and division
of power, I operated for the first time an electric power hammer that I
shall here describe. Its essential part is a sectional solenoid that
I have likewise made an application of in an electric motor which I
presented in July, 1830, to the Societe de Physique. Let us suppose we