APPLICATION OF THE ELECTRIC TELEGRAPH. 319 



is attached to the pendulum in such a position that, at 

 every vibration of the pendulum, the pin slightly im- 

 pinges upon .the angle C, of the platinum wire and forces 

 up the end A. As soon as the pin has passed the point 

 C, the end A falls back again upon its support D. Thus 

 at every vibration of the pendulum, the end of the plati- 

 num wire is lifted about a tenth of a second, and rests 

 upon D during the remaining nine tenths of the second ; 

 that is, the electric circuit is closed about nine tenths of 

 every second, and is open during the remaining tenth. 



The method first proposed by Mr. Saxton in 1844, is 

 the one which has been employed at the "Washington 

 observatory since 1849. A small piece of metal M is 

 attached to the back of the clock, near 

 the lower extremity of the pendulum, 

 and upon it is placed a small globule of 

 mercury, so that the index B attached to 

 the lower extremity of the pendulum may 

 pass through the globule of mercury once 

 in every vibration. A wire from one 

 pole of the battery is connected with the 

 supports of the pendulum C, and a second 

 wire from the other pole of the battery 

 connects with the metallic support of the 

 mercury globule. If now the pendulum 

 were at rest, with the point B in the 

 mercury, it is evident that the electric 

 circuit would be complete through the 

 pendulum. If then the pendulum be set in motion, it 



