APPLICATION OF THE ELECTRIC TELEGRAPH. 313 



tween Philadelphia and Cincinnati 37 minutes 20.48 

 seconds. . 



In the course of the comparisons for longitude by tele- 

 graph, up to the autumn of 1848, many thousand signals 

 were transmitted, and all by the hands of a human 

 operator. But it is impossible for human fingers to 

 move with the precision of machinery; and, after the 

 first successful trial of the telegraph for longitude, it 

 became evident that an important advantage would be 

 secured if the clock could be made to transmit its own 

 signals. The desideratum was to make an astronomical 

 clock break the electric circuit every second, so that prac- 

 tically it might be said that its beats could be heard along 

 the entire line of telegraph communication ; and this 

 must be done in such a manner as not to affect the rate 

 of the clock. A number of different methods of ac- 

 complishing this object were speedily proposed ; but as 

 several contrivances of a similar kind had previously 

 existed, it is thought best to notice them all in chrono- 

 logical order. 



THE ELECTRIC CIRCUIT BROKEN BY A CLOCK. 



The first invention for breaking the electric current by 

 clock-work appears to be due to Professor Steinheil, of 

 Munich, who previous to September, 1839, had perfected 

 a method for causing any number of clocks to indicate 

 exactly the same time.* This was accomplished by 

 means of an arrangement which enabled the regulating 



* Moigno'a Traite de Telegraphie Electrique, page 337. 

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