HISTORY AND PROGRESS. 39 



The first alarm employed by him was an apparatus in 

 which the attraction of a soft iron armature to the cores of 

 an electro-magnet, whose coils were in connection with the 

 line, released a wound-up mechanism. 



This alarm arrangement is given in Fig. 20. The tooth- 

 wheel n was arrested by the end of the lever p. On the other 

 end of p was a soft iron armature, ?, which, when a current 

 passed through the coil u of the electro-magnet, was attracted, 

 and released the wheel. The case contained a clockwork 

 surmounted by a bell, which was struck by a hammer, moved 

 backwards and forwards by means of an eccentric. 



At the sending station were a small battery, K, and a key, 



Fig. 20. 



s, consisting of two metallic springs, a b, of which the lower 

 one, b, was fixed on a block of wood, and insulated from the 

 other by a strip of ivory. The spring a could be pressed 

 against b ; but when untouched, remained separated from it 

 by its own elasticity. 



From the positive pole of the battery, a wire, 1, went to 

 the electro-magnet, u, of the alarm, and was turned several 

 times round the horns of soft iron ; a second wire, 2, returned 

 to the transmitting station, where the line was connected 



