Another method of working single lines which has been introduced within a comparatively recent period is what is known as the "Train Tablet System," which is now in operation on a section of the line at Cockermouth, on the Callander and Oban railway in Scotland, and elsewhere. Although the train staff system, as described above, combined with the block telegraph, has answered its purpose well, it has one drawback, which is that the sections have of necessity to be short in order to avoid serious delays, and under any circumstances it may occur that the train staff may be at one end of the section while a train is waiting for it at the other. This fact led one of the officers of the Caledonian Company to set his wits to work to devise an arrangement by which a train staff, or its equivalent in the form of a tablet, or circular disc of metal, could be electrically controlled from the other end of the section, so as to constitute in point of fact a train staff and block telegraph system combined.
The apparatus has been since improved and perfected, and has been patented by Messrs. Tyer & Co., the well-known electrical engineers. Although the working is, in practice, very simple, a detailed description of the instruments used, and the way in which they are manipulated, would appear extremely complicated, but the essential features of the system are as follows:—Supposing A and B are the two ends of a section of single line and a train is waiting at A to proceed to B. The signalman at A gives a signal to that effect on an electric bell to the signalman at B. If, according to the block telegraph regulations, the train may proceed to B, that is to say if the line to the knowledge of the signalman at B is clear between A and B, the signalman
