REPORT OF MR. ROBERT B. LINES.
445
" cuts the magnet out.” The magnet ceasing to act, the armature is drawn back by the force of the spring. But this reestablishes the circuit through the coils, the armature is a^ain attracted, and the hammer again strikes the bell. It is evident that the armature will continue to vibrate and the bell to ring as long as the circuit is closed at m s. The train thus announces its own approach by signal, which, it is true, lasts only as long as the train is passing, but which can be made permanent if necessary, by the introduction of a very slight modification in the apparatus.
The use of the lever at the side of the track was introduced in America, by Mr. Thomas Hall, in 1869, in connection with apparatus which will be hereafter alluded to.
The trembling-sounder, here described, fills an important place in the signal systems of Europe. On the continent, the law generally requires gates to be placed at grade crossings of common roads, which are shut for a certain time before the passage of every train. On some of the lines in France, the gatekeepers are advised electrically of the approach of trains by the use of the trembling-sounder, in order to close their gates. The attention of the gatekeepers, which might not be drawn in time for them to interpret any preconcerted code, is attracted by a continuous signal, which has .but one meaning. As it is unnecessary that the gatekeepers should know either the character of the train or the direction from which it is approaching, a number of signal- boxes are sometimes placed on the same circuit and operated at the same time. The principal use of thi% arrangement is in the vicinity of towns, where crossings are near together. The signals, in the arrangement described, are of course sent from fixed stations. They are not properly " warning-signals,” of which I propose to treat under Group III.
The trembling-sounder is again extensively employed throughout Europe for giving notice at stations of the position of outlying switches and semaphores, and it is, therefore, proper to introduce the second branch of my subject by a short notice of its application to such purpose.