The levers in the particular type of locking gear which we are considering have each a tailpiece or "tappet arm" attached to it, which moves backwards and forwards with the lever (Fig. 93). Running at right angles to this tappet, and close to it, either under or above, are the lock bars, or stud bars. Refer now to Fig. 94, which shows the ends of the three tappet arms, D, H, and S, crossed by a bar, B, from which project these studs. The levers are all forward and the signals all "on." If the signalman tried to pull the lever attached to D down the page, as it were, he would fail to move it on account of the stud _a_, which engages with a notch in D. Before this stud can be got free of the notch the tappets H and S must be pulled over, so as to bring their notches in line with studs _b_ and _c_ (Fig. 95). The signalman can now move D, since the notch easily pushes the stud _a_ to the left (Fig. 96). The signals must be restored to danger. As H and S are back-locked by D--that is, prevented by D from being put back into their normal positions--D must be moved first. The interlocking of the three signals described is merely repeated in the interlocking of a large number of signals. [Illustration: FIG. 94.] [Illustration: FIG. 95.] On entering a signal-box a visitor will notice that the levers have different colours:--_Green_, signifying distant signals; _red_, signifying home and starting signals; _blue_, signifying facing points; _black_, signifying trailing points; _white_, signifying spare levers. These different colours help the signalman to pick out the right levers easily. To the front of each lever is attached a small brass tablet bearing certain numbers; one in large figures on the top, then a line, and other numbers in small figures beneath. The large number is that of the lever itself; the others, called _leads_, refer to levers which must be pulled before that particular lever can be released. [Illustration: FIG. 96.] [Illustration: FIG. 97.--Model signal equipment in a signalling school. (By permission of the "G.W.R. Magazine").] POINTS. Mention was made, in connection with the lever, of _points_. Before going further we will glance at the action of these devices for enabling a train to run from one set of rails to another. Figs. 98 and 99 show the points at a simple junction. It will be noticed that the rails of the line to the left of the points are continued as the outer rails of the main and branch lines. The inner rails come to a sharp V-point, and to the left of this are the two short rails which, by means of shifting portions, decide the direction of a train's travel. In Fig. 98 the main line is open; in Fig. 99, the branch. The shifting parts are kept properly spaced by cross bars (or tie-rods), A A. [Illustration: FIG. 98.--Points open to main line.] [Illustration: FIG. 99.--Points open to branch line.]