APPLICATION OF THE ELECTRIC TELEGRAPH. 315 



time in as many different places as may be required.* 

 In the electro-magnetic clock, all the parts employed in 

 an ordinary clock for maintaining and regulating the 

 power are entirely dispensed with. It consists simply of 

 a face with its second, minute, and hour hands, and of a 

 train of wheels which communicate motion from the 

 arbor of the second's hand to that of the hour hand, in 

 the same manner as in an ordinary clock train. A small 

 electro-magnet is caused to act upon a peculiarly con- 

 structed wheel, placed on the second's arbor, in such a 

 manner that whenever the temporary magnetism is either 

 produced or destroyed, the wheel, and consequently the 

 second's hand, advances a sixtieth part of its revolution. 

 It is obvious then that if an electric current can be alter- 

 nately established and arrested, each resumption and 

 cessation lasting for a second, the instrument now de- 

 scribed, although unprovided with any internal maintain- 

 ing or regulating power, would perform all the usual 

 functions of a perfect clock. The manner in which this 

 apparatus is applied to the clocks, so that the movements 

 of the hands of both may be perfectly simultaneous is the 

 following : 



On the axis which carries the scapement wheel of the 

 primary clock, is fixed a small disc of brass, which is 

 first divided on its circumference into sixty equal parts ; 

 each alternate division is then cut out and filled with a 

 piece of wood, so that the circumference consists of 

 thirty ^regular alternations of wood and metal. An ex- 



* Abstracts of the Philosophical Transactions vol iv., page 249. 



