33 6 



THE POPULAR SCIENCE MONTHLY. 



cable, and a system adopted whereby the clock is automatically " set 

 to time " every hour, or at such intervals as may be arranged. The 

 apparatus can here be described only in brief. There are three essen- 

 tial parts, the standard clock, the distributor, and the synchronizer. 



The standard clock is an astronomical regulator with mercurial 

 pendulum and dead-beat escapement, and closes an electric circuit at 

 the sixtieth second of each hour. Another regulator, technically called 

 " Lobby," is for use in case of accident to " Standard." They are so 

 connected that a single failure of " Standard " to send out a signal at 

 the proper time brings " Lobby " into action for the next signal, and, 

 in order that " Lobby " may always be ready for service, an inten- 

 tional breakdown of " Standard " occurs automatically at eight each 

 morning, and the nine o'clock signal is sent out by " Lobby " ; which 

 of the two is in operation is shown by indicators connected with the 

 clocks (Fig. 10).* Should a breakdown occur, the indicator of " Stand- 

 ard " would show missed, and that of " Lobby " at work. 



Fig. 10. Baeratjd and Ltjnd's Indicatoes. 



The error of the standard clock is determined daily by comparison 

 with the Greenwich signal. An ordinary dotting chronograph is set 

 to the standard clock, and the Greenwich signal makes a dot on the 

 chronograph-dial which gives at once the error of the standard and 

 can be read off at leisure. It is corrected by electric means. The 

 pendulum carries a small permanent magnet which swings over a re- 

 sistance-coil about -j 1 ^ inch distant. The coil is connected with the 

 commutator in the test-box (Fig. 11), consisting of a clock commuta- 

 tor with plugs for " Standard " and " Lobby," a current commutator 

 with plugs for " Fast " and " Slow," and a small time-piece, shown at 

 the top. The time-piece has only a minute-hand, and is made so as to 

 stop itself and break circuit at XII, but closes circuit when running. 

 The working is thus : Suppose " Standard " is found to be slow. Plugs 

 are inserted for " Standard " and " Slow," and the hand of the time- 

 piece is set back a required number of minutes. It then runs to XII 

 and stops. In this interval the action between the magnet and the 

 coil has exactly corrected the standard clock. For every -fa second of 



* Figs. 10, 11, 12, and 13, hare been reduced from drawings in "The Railway Engi- 

 neer," London, by permission of Messrs. Barraud & Lund. 



