THE ELECTEIC TELEGRAPH. 



Fig. 71. 



192. Its mode of operation. 193. How errors are corrected. 194. 

 Explanation of the mechanism. 195. Comparison with the French 

 telegraph. 196. Indicating mechanism. 197. Simplicity greater than 

 the French instrument. 198. Requires greater intensity of current. 

 199. Belgian railway telegraph. 200. Defects imputed to the French 

 and German instrument. 



184. IT remains, therefore, to show the manner in which, the 

 pulsations of the current are governed by the commutator. 

 One of the commutators is represented in fig. 71. 

 The handle M is fixed upon an axis which turns in the centre of 

 a fixed disc D, the edge of which is divided into eight equal parts 



by small notches. A short pin 

 projects from the handle which 

 falls successively into these 

 notches, but which can be with- 

 drawn from them when it is re- 

 quired to turn it. On the remote 

 end of this axis a disc is fixed, 

 which turns with it, in the face of 

 which a square groove is cut, 

 rounded at the corners, in which 

 a pin projecting from a short 

 lever I is moved. This lever I is 

 fixed on the axis c c, upon the 

 other end of which is fixed the 

 lever L, the lower end of which 

 carries a small piece of metal r, 

 which, when the lever vibrates 

 right and left, is thrown alter- 

 nately against the contact-pieces 

 x and x'. 



Supposing that the commutator 

 is placed at the station s, the 

 line-wire which comes from the 

 station s' enters the foot, and is 



held there by a tightening screw A. This wire is in metallic con- 

 nection, through the pillar, with the lever L, and consequently 

 with the piece of metal at its lower end, which oscillates between 

 the contact-pieces x and x'. This piece of metal, r, may therefore 

 be considered as virtually the extremity of the conducting wire 

 between the stations s and s'. 



Attached in like manner, by tightening-screws, to the two 



contact-pieces K and x' are two wires, one of which is connected 



with the battery, and the other with one end of the coil- wire of 



the electro-magnet, in the indicating instrument of the station s. 



18 



