THE ELECTRIC TELEGRAPH. 



The apparatus of M. Lippens, which is now used for the service 

 of the Belgian railways, is exempt from these defects. 



Like M. Siemens, M. Lippens rejects the mainspring and its 

 appendages adopted in the French telegraphs, and charges the 

 current itself with their functions. He retains, however, the 

 commutator, and imparts the pulsations to the current by the 

 hand of the agent applied to a lever or winch, which is moved 

 exactly like the arm of the commutator of the French 

 instruments. 



He rejects the spring 5 (fig. 77), which produces the recoil of 

 the armature, and substitutes for it a second magnet placed on , 

 the other side of the armature, substituting at the same time a 

 permanently magnetic bar of steel for the armature of soft iron 

 used in the other instruments. 



202. To explain the principle of Lippens' apparatus, let a I and 

 a* b' (fig. 78) be two electro-magnets made precisely alike, the 

 Fig> 78t coil of covered wire 



upon them being one 

 continuous wire carried 

 from one to the other, 

 and rolled in such a 

 manner that their po- 

 larity shall always have 

 contrary positions in 

 whichever direction the 

 current may be trans- 

 mitted on the wire. 

 Thus, if a be a north 



pole, b f opposed to it will be a south pole, and in that case 

 a' will be a north and b a south pole. If the current upon the 

 coil be reversed, all these four poles will at once change their 

 names a becoming a south and b' a north pole, and a' a south 

 and b a north pole. 



Let g g f be a steel bar which is permanently magnetised, g 

 being its north and (f its south pole, and let it be supported 

 midway between the electro-magnets, having free play towards 

 the one or the other until it encounters the stops it or if V by 

 which it is arrested. 



Now let a current be transmitted upon the wire, by which a 

 will become a north pole, and consequently b and b' will be south 

 poles, and a' a north pole. Since g is a north and $ a south pole, 

 they will be attracted by b' and a', and repelled by a and b, and 

 consequently the armature g g 1 will be moved towards b' a' until 

 it is stopped by t' f. If the current be then reversed, a and a' 

 will become south, and b and b' north poles ; and the armature 



