at B draws out a slide in his instrument, and depresses a plunger, which, by means of an electric current, has the effect of enabling the signalman at A to draw out a corresponding slide in his instrument, and remove from it a train tablet, which he hands to the driver of the train as his authority to start and enter the section in advance towards B. On arrival at B the driver delivers up the tablet to the signalman there, who inserts it in his instrument, and until this has been done, the apparatus is automatically locked, and a second tablet cannot be obtained from the apparatus at either end. Thus it is impossible for two trains to be in the same section at the same time, proceeding in opposite directions, although trains may follow one another in the same direction at the proper intervals without intermission or delay.
An apparatus very similar to this, and designed to attain the same objects, has recently been devised and constructed at the Crewe works, and is now in use on the Bedford and Cambridge branch, having been approved by the Board of Trade. In this case train staffs of the ordinary type take the place of the tablets, and these are made in such a form, that they will serve to open any of the intermediate sidings within the section, which in their normal state are locked. Although the apparatus differs in form, the manipulation is almost identical with that of the train tablet system, it being physically impossible for a staff to be withdrawn without the concurrence of the signalmen at the two ends of the section. The experimental trial of this system having proved very successful, it will probably be extended to other single line branches.
There is one element which causes, perhaps, more difficulty, and entails more anxiety upon those engaged
