332 THE POPULAR SCIENCE MONTHLY. 



of jointed vertical bars (B, B', B"), which, except at the times for the 

 signal, are kept in contact by springs with cocks in the circuit of the 

 wire ; but at the times for the signal a long metallic bar (C) acting as 

 a cam (better shown in Fig. 7, in front of the vertical bars), is made 

 by clock-work to disconnect all these bars from their instruments. The 

 bar (C) is divided into three parts, corresponding to the long, medium, 

 and short provincial lines, insulated from each other, and connected 

 respectively with the bars of the relays (V, V, V") through the galva- 

 nometers (g, g', g", Fig. 8). The left or rest contacts of these relays 

 are in connection with the zinc poles of separate batteries, whose cop- 

 per poles are grounded, so that, when the bars of these relays are put 

 in connection with the line wires, a zinc or " preliminary " current is 

 ready to be sent out ; this current prevents the distant relays from 

 being actuated by contacts or accidental currents, and serves as a 

 warning signal. The right-hand contacts of the relays are connected 

 respectively with the copper poles of separate batteries whose zinc poles 

 are grounded, so that, when the bars are moved over to the right (which 

 is done by the incoming Greenwich current), the outgoing current is 

 reversed, and this constitutes the signal. The relay V" is for dis- 

 tributing the signals only to points in the metropolis, and, as the wires 

 on these lines are under ground, no " preliminary " current is necessary. 

 ' The mechanical operation of the apparatus is as follows : On the 

 clock (R, Fig. 9) there is an ebonite wheel ( W) in which are two notches 

 (N, N') corresponding to 10 A. M. and 1 p. m. Shortly before 10 a. m. 

 the pin (P) on one arm of the forked lever (L) falls into the notch (N), 

 allowing the end (Q) of the other arm to rest on the ebonite hour- 

 wheel (T). About two minutes before the hour, the end (Q) comes 

 against the contact (S), and completes the circuit of the local bat- 

 tery (IT, Fig. 8) through the starting magnet (M, Fig. 9) and sets the 

 clock-train (shown in Fig. 7) in motion, pressing the cam (C) against the 

 vertical bars, disconnecting them from their instruments, and connect- 

 ing them respectively, in groups as already shown, with the relays 

 (V, V, V"), in readiness to send a " preliminary " current to the line 

 wires. At ten seconds to the hour an insulated pin (i, Fig. 9) on the 

 wheel (T) lifts the lower arm of the forked lever (F),so that its upper 

 arm comes in contact with a small cam on the arbor of the escape- 

 wheel (K). This contact closes the circuit of the battery (U) through 

 the coils of the two relays (Z, Z'). The relay (Z) puts on the earth con- 

 nection at (E), for the four relays (V, V,' V", V"), so that the current 

 from Greenwich may be received and divided between them, while 

 the relay (Z') disconnects the Westminster clock-wire and connects it 

 with the metropolitan lines to receive the signal from the relay (V"). 

 The relays (V, V, V", V") have a resistance of 5,000 ohms to allow 

 of the splitting of the current. At precisely ten o'clock the Green- 

 wich signal reverses the current on the lines, and thus gives the exact 

 time. At ten seconds past the hour the contact between H and K is 



