440
'EXPOSITION AT VIENNA.
To illustrate the arrangement of signal stations between © ©
which the movement of trains only is desired to be shown,—
Plate I.
A
C
Let A, B and C (Plate I.) be three adjacent signal-stations, or boxes. A and C are, of course, fitted up exactly as B; but it being only necessary to describe one set of apparatus, those at A and C are omitted from the drawing. M M are magnets placed upon the lines L L, which, after passing through the coils of the magnets at A, B and C, are connected to the ground G, through the commutators, or switches, c c c c. In their normal condition, therefore, there is no electric current passing on the lines on either side of B. This is the ordinary arrangement of what is called an " open circuit.” *
Suppose now that a train passes A, whose approach he wishes to signal to B. By turning the switch c to the left, the current from the galvanic battery g is thrown on the line through the pointy? and the switch. The magnet M, being influenced by the current, attracts the armature a, and the hammer h at the upper extremity of the armature strikes against the bell b. The stroke, of course, continues as long, and is renewed as often, as the switch is thrown upon the pointy?. The instrument is enclosed in a box, as shown in the figure, and placed against the wall of the station, or at any other convenient spot, the bell and armature being protected from exposure by means of a zinc cap z.
* Objection has been made to the use of the open circuit with one wire for signals, on account of the momentary signals which might be produced by atmospheric electricity seeking its way through the wire to the ground, or by what are known as “ earth currents.” But as the object of the above description is simply to illustrate the action of the “ bell-sounder ” under the influence of any electric current, these objections need not here be considered.