(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 for this purpose those small apparatus that have been styled semaphore repeaters.

Mr. Lartigue has invented two automatic apparatus, by means of which the train itself signals its approach.

1.  The first of these, which is generally placed at about 6,000 feet from the point to be covered, consists (Figs. 5, 6, 7, and 8) of a very light pedal fixed to the inside of the rail, and acting upon a mercurial commutator.  A spring, R, carried upon the arm, a, of a lever, A, projects slightly above the level of the rail, while the other arm, b, carries a commutator.

The spring, R, on being depressed tilts the box containing the mercury, closes the circuit, and causes an alarm, S, located at the crossing, to immediately ring.  In this alarm (Fig. 8) a piece, P, is disconnected by the passage of the current into the electro-magnet, E, which attracts the armature, a, and, a permanent current being set up, the apparatus operates like an ordinary alarm, until the piece, P, is placed by hand in its first position again.

2.  The second apparatus, exhibited by the Railway Company of the North, and also the invention of Mr. Lartigue, bears the name of the “Bellows Pedal.”  It consists (Figs. 9 and 10) of a pedal, properly so called, P, placed along the rail, one of its extremities forming a lever and the other being provided with a counterpoise, C. When a train passes over the pedal, the arm, B, fixed to its axle, on falling closes the circuit of an ordinary electrical alarm, and at the same time the bellows, S, becomes rapidly filled with air, and, after the passage of the train, is emptied again very slowly under the action of the counterpoise.  The contact is thus kept up for some few minutes.  This apparatus works very satisfactorily, but is cumbersome and relatively high-priced.