APPLICATION OP THE ELECTKIC TELEGRAPH. 323 



consisting of an indented line about nine tenths of an 

 inch in length, followed by a blank space of about one 

 tenth of an- inch. 



The Congress of the United States have expressed 

 their conviction of the importance of this invention, by 

 awarding the sum of ten thousand dollars to Dr. Locke 

 for his invention, and directing that a clock upon this 

 principle should be constructed for the use of the ob- 

 servatory at Washington. This clock was completed in 

 1850, and has been set up for use at the observatory. 



In 1849 Professor O. M. Mitchell, of Cincinnati, in- 

 vented a method of breaking the electric circuit by means 

 of a delicate .fibre attached to the pendulum which acts 

 upon a cruciform lever, and thus, in every vibration of 

 the pendulum, allows a metallic point to dip into a cup 

 of mercury, which completes the circuit In the annexed 

 figure, A B represents the lower extremity of the pen- 



dulum; B C is a delicate fibre, one end of which is 

 attached to the pendulum, and the other to one arm of 



