MORSES TELEGRAPH. 



of which any of the keys when pressed by the finger will lower it. 

 This bar rests upon the arm of the catch engaged in the teeth 

 of the ratchet-wheel, so that whenever any key is put down by 

 the finger, the bar is depressed, the catch disengaged, the wheel 

 liberated, and a motion of revolution imparted. 



On the left hand extremity of the steel rod is fixed a commu- 

 tating wheel, similar in principle to that already described in the 

 railway telegraph. This wheel, being fixed upon the rod, turns with 

 it, moving when it moves, and stopping when it stops. Since the 

 position in which the rod stops is determined by the key put down, 

 the position in which the wheel thus fixed on the rod stops, is 

 similarly determined. This wheel determines the pulsation of the 

 current, and these pulsations determine the position of the 

 indicator at the station to which the despatch is transmitted, in a 

 manner which is substantially the same as that already described 

 in the case of the railway telegraph. 



FOSSE'S TELEGKAPH. 



206. This apparatus, which is applied on an extensive scale in 

 America, and with some slight modifications in the Germanic States, 

 is constructed upon the principle already explained in 153. 



Fig. 82. 



A general view of the instrument in its most usual form is- 

 given in fig. 82. 



i is the electro-magnet ; H is an armature working on the centre 

 c ; i an adjusting screw to limit the play of the armature, and 

 prevent its contact with the electro-magnet at p ; d another 

 adjusting screw to limit its play in the other direction ; t a metallic 



41 



