322 



HISTOKY OF ASTRONOMY. 



by means of a tilt-hammer. Dr. Locke employs a wheel 

 with sixty teeth attached to the axis of the escapement 

 wheel. Bach tooth in succession strikes against the 

 handle of a platinum tilt-hammer, A C, weighing about 

 two grains, and knocks up the hammer, which almost 

 immediately falls to a state of rest on a bed of platinum. 



The fulcrum B of the tilt-hammer and the platinum 

 bed rest severally on a small block of wood. Each is 

 connected "by wires D and E with a pole of the galvanic 

 battery, and the circuit is alternately broken and com- 

 pleted by the rising and falling of the hammer. The 

 circuit is open about the one tenth of a second, and 

 closed the remaining nine tenths of each second. This 

 arrangement was first tested on the 17th of November, 

 1848, on the Cincinnati and Pittsburg line, about four 

 hundred miles in length. The circuit was broken every 

 second by the motion of the clock; and the fillet of 

 paper being allowed to run off from the reel of the tele- 

 graph register, it was graduated into equal portions, 



