the movement of the maneuvering lever.

The apparatus, which is represented in the accompanying Figs. 1, 2, 3,
and 4, consists of the following parts:

(1.) A mercurial commutator, O, which is fixed on a lever, B,
connected with a piece, A, which is applied against the external
surface of the web of the main rails, opposite the extremity of the
switch plates;

(2.) A bar, C, which traverses the web of the rail and projects on the
opposite side, and which carries a nut, D, against which the switch
plate abuts;

(3.) An electrical alarm and a pile, located near the switch lever.
As long as one of the two plates of the switch is applied against the
rail, one of the two commutators is inclined and no current passes. A
space of one millimeter is sufficient to bring the commutator to a
horizontal position and to cause the electric alarm to ring
continuously. If the apparatus gets out of order, it is known at once;
for if the alarm does not work during the maneuver of the switch, the
tender will be warned that the electric communications are
interrupted, and that he must consequently at once make known the
position of his switch until the necessary repairs have been made.

_Pedals for Transmitting Signals to Crossings._--On railways having a
double track and doing a large amount of business it becomes very
necessary to announce to the flagmen at railway crossings the approach
of trains, so as to give them time to stop all crossing of the tracks.
On railway lines provided with electro-semaphores there may be used