76 THE ELECTRIC TELEGRAPH. 



the letter to be indicated ; and B, the receiving instrument, 

 supported by a bracket at the back. The latter has in front 

 a small dial, corresponding in its arrangement with that 

 of the transmitter, and a pointer whose motions follow 



Fig. 39. 



faithfully those of the handle of the instrument which is 

 working. 



Fig. 40 shows the internal mechanism of the transmitter. 

 The metal disc J, with inclined teeth on its rim, is supported 

 by the back #, and by two square pillars y. On the back, 

 which consists of a stout plate of soft iron, are screwed a 

 series of several pairs of permanent magnets, G G ; those 

 on one side with their north, and those on the other with 

 their south poles projecting. 



Between the poles of this system is a cylinder of soft 

 iron, E, which serves as keeper of all the magnets. It is 

 cut out longitudinally in two deep, broad grooves, on opposite 

 sides, in which a spiral of fine well- insulated copper wire is 

 coiled. The whole armature is supported by the brass caps 

 F F', in pivots above and below. Above the spiral, the 

 pinion T locks into the tooth- wheel L, turning on an arbor 

 A A, by means of the handle H above the disc J. The pro- 

 portion between the teeth of the wheel and those of the 

 pinion is such that one revolution of the wheel causes the 

 pinion to revolve thirteen times, changing the magnetism 

 along the whole length on each side of the armature, and 



