110 MR. H, WILDE ON A PROPERTY OF 



with the alternations of the current. As the amplitude 

 of the oscillations in this experiment was limited by the 

 vis inerticB of the armature^ and in order that the effect of 

 one pulsation only on the armature might be observed, 

 contact was made and broken suddenly between the plate 

 H and the end G- of the coil, when the stationary arma- 

 ture was suddenly jerked round nearly a quarter of a 

 revolution, sometimes in the direction in which it would 

 have been driven by the strap, and at other times in the 

 opposite direction, according as the alternating electrical 

 wave which happened to be passing at the instant of 

 making contact was positive or negative. 



We have now seen, in the results obtained with the 

 rotating and stationary armatures, a cause sufficient to 

 account for their synchronism when revolving together, — 

 the absence of synchronism observed when the terminals 

 F and H were bridged over by a conductor having com- 

 paratively little or no resistance being occasioned by the 

 controlling current traversing the short circuit established 

 between the terminals F and H, instead of the 280 feet of 

 resistance presented by either of the coils when approach- 

 ing the neutral point of their revolution. The absence of 

 synchronism observed when the direct current was taken 

 from the machines by means of commutators, is caused 

 by the direction of the current being coincident with that 

 which they would receive by induction from the electro- 

 magnets, and consequently opposite to that which tends 

 to impart an accelerating or retarding impulse to the 

 armatures. 



Having obtained the full effect of the combined alter- 

 nating currents from the two machines without any 

 mechanical gearing, it yet remained to obtain the combined 

 direct currents from the machines in the same manner. 

 A pair of rings and a commutator were therefore fitted 



