THE MAGNETO-ELECTRIC CURRENT. 109 



whenever contact between G and H was made and broken^ 

 a bright spark appeared at the point of disjunction so long 

 as the rotation was not synchronous ; but when the syn- 

 chronism was reestablished, only a trifling residual spark 

 was visible. 



Although the synchronous rotation was preserved when 

 the terminals FH, from which the combined current was 

 transmitted, were disconnected from the electric lamp, yet 

 it will be seen, from an inspection of the diagram, that a 

 complete metallic circuit was in fact always formed between 

 these terminals through the coils themselves. Now, when 

 the coils DD happen to be at the same moment in that 

 position during their revolution in which they are produ- 

 cing the maximum and minimum amount of current 

 respectively, as must often be the case where there is no 

 synchronism, that current which is at the maximum rushes 

 through the coil which is producing the minimum current, 

 as is shown by the spark at the point where contact is 

 broken between Gr and H. The eff'ect of this passage of 

 the current from one coil to the other is to accelerate or 

 retard the rotation of the armature (according to the 

 direction of the current) until synchronism is established. 



That this influence of one coil upon the other operates 

 in the manner described was easily shown by the following 

 experiment : — The driving-strap of one of the armatures 

 was removed, so that only one of the armatures should be 

 producing a current, while the magnetism of the electro- 

 magnets of both machines was, as usual, maintained to 

 the same degree. On placing the stationary armature 

 with its coil in a suitable position in relation to the 

 magnet-cylinder for producing electromagnetic rotation, 

 and settiug the other armature in motion, the stationary 

 armature with its coil oscillated rapidly in arcs of very 

 small amplitude, the oscillations corresponding in number 



