152 



Mr. Julius Frith on 



but most especially the third, the second being in most cases 

 comparatively small. 



Description of Machine. — The Wilde alternator used con- 

 sists of two crowns of cast-iron facing each other ; from 

 the internal surfaces of these crowns project the fixed field 

 coils, six in number, on each side. These are bobbins ot 

 wire wound on iron cores. The armature revolves between 

 these, and consists of six similar bobbins on tubular iron 

 cores, held in position between two discs of brass which are 

 keyed on to the shaft. The six coils of the armature are 

 connected in series to the commutator. 



Fig. 1. 

 D = Wilde alternator. 



R = Resistance, without self-induction. 



C = Ammeter. 



E = Electrometer. 



B = Two insulated brushes bearing on the ebonite disc which carries 



the copper contact piece. 



Principle of Intermittent Contact. — On the end of the 

 shaft beyond the commutator is keyed an ebonite disc ; in 

 a slot cut in this, about T V inch wide, a piece of copper is 

 fixed, and turned down flush with the ebonite. On this 

 disc bear two insulated brushes, side by side ; it will be 

 seen that at one instant in every revolution these two 

 brushes are connected together, while remaining insulated 

 from the rest of the machine. If one of these brushes 

 is connected to one pole of the dynamo, and wires are 



