Engineering Wonders of the World
Volume I

238 ENGINEERING WONDERS OF THE WORLD. Fig. 23.—SIGNAL BOX AT EARL’S COURT EAST STATION. The signalman is aided by a map on which the movements of signals and points are shown by electric lamps. two is an even number. The system of working will be made clear by Fig. 24. Here we have four sections. Section 2 is controlled by the staffs in instruments B and B1, section 3 by those in C and C1. Trains T1, T2 are travelling from right to left and from left to right respec- tively. On reaching station X, the driver of T1 hands over his A staff, which is inserted in a Single Line. instrument A. At the time of his arrival B contains 9 and B1 contains 11 staffs (making 20 in all), so the signalman is able to remove a B staff and hand it over. T1 proceeds, while another train following behind reaches X. This train is blocked, however, as the number of B staffs in the instruments is now only 19, and no more can be ab- stracted until T1 delivers its staff at B1. The train T2, travelling from Z to Y, has blocked section 3. At station Y the two trains hand over their staffs, which put the B and C instruments “ in step ” again, and clear sections 2 and 3. Con- sequently both trains are able to proceed. When T1 has surrendered its C staff at key on the staff, in the absence of the latter no more tickets could be delivered. Delays often arose, however, from trains having to wait for the return of the staff ; and this led to the introduction of the Electric Tablet, and subsequently the The Electric g|ectr|c Train staff System. Train Staff. Å , , „ , , , At each end of a block section is provided an instrument into which a con- siderable number of the staffs or tablets belonging to that section, and that section only, may be inserted. The two in- struments are electrically con- nected, and so control each other that a staff can be re- moved from either only when the sum of the staffs in the C1, and T2 its B staff at B, the road is clear for T3 following T1 from X to Z. The number of staffs assigned to each section is sufficiently great to allow several trains to pass in the one direction without exhausting the supply, even if none are returned by trains moving in the opposite direction. It should be added that the signal boxes where the instruments are placed have Section 4 StaSej ___ t»O-» StationZ Section3. SutionY Section 2 StationX Sectionl ... „ . t-OT'- O C'(iO) (ioj 2 (9)8 A t2 C Staff ,, , o-» B Staffel " 2 D C'tø) (ICOC B'OO (8) B Ä C Staff , B staff <-OT' . , TaQ-* ,07 s " 3 . - - D C'(9) (io)d B’OV (8)BA D Staff . 4 st )T'_. » ,cT oT4AStaff 0 C'(1O) (1O)C B'(ll) (?) B A Fig. 24.