TIME-KEEPING IN LONDON. 



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hollow galvanic coil, called " the accelerating or retarding coil," fast- 

 ened to the clock-case and operated by a special battery. The attrac- 

 tion or repulsion, between the magnet and the coil, produced by send- 

 ing currents in opposite directions, gives any required acceleration or 



retardation to the pendulum. Care must, of course, be taken that the 

 correction be not made too quickly, else the clock, instead of being 

 controlled by the current, will break away from control, and the error 

 will be increased. It is now so arranged that the current will produce 



