CURRENT REVERSERS 71 



drums therefore start off on a fresh revolution in 

 unison. 



The reverser is of various forms, and is, of 

 course, used in most electrical instruments which 

 require similar synchronisation. One pattern of it 

 is seen in Fig. 32. Here, M, N are two steel 

 tongues with platinum contacts attached to a bar 

 which can rotate about a fulcrum 1 F ; it is held in 

 position by a spring S, the end of which is attached 



FIG. 33. 



to a point T, in this case in the bed -plate. 

 A represents a projecting pin on the cylinder or 

 drum, which, in the position shown, depresses the 

 end of the bar and consequently causes the tongues 

 M, N to rise. As soon as the drum has travelled a 

 little further round, the pin A is out of the way, 

 hence the spring S pulls the tongues M, N down 

 again into their normal position. 



The next diagram (Fig. 33) represents the revers- 

 ing arrangement. M, N are again the tongues, 

 while P, Q and R, S are four platinum contact pins. 



