274 
THE TELEGRAPH, 
current is made constantly to pass between each pair of con¬ 
secutive stations, so that if the current be interrupted and re¬ 
established at any point, a hammer will strike one blow on the 
corresponding bell. The apparatus at the stations is composed 
of a loud bell, the hammer of which is connected to an electro¬ 
magnet by rods and levers properly arranged (fig. 191). 
These levers are moved by wheelwork, A, set in motion by 
a weight and regulated by the intermittent motion of an 
escapement controlled by the electro-magnet. 
The apparatus placed along the line consist of large bells 
attached to the signal cabins (fig. 192), and acted on as in the 
former case. But in the apparatus along the line the wire 
wound round the electro-magnet is, of course, connected at each 
end with the line wire. 
By varying the number of strokes on the bell and the 
length of the intervals of time between them, different signals 
