THE MAGNETO-ELECTRIC CURRENT. Ill 



upon one of the armature-spindles, which was made 

 sufficiently long for the purpose, and metallic connexion 

 was established between the rings of each machine and 

 the commutator on the prolongation of the armature-axis. 

 As the commutator necessarily revolved synchronously 

 with the two armatures, it was found that the combined 

 alternating currents were rectified just as if they had 

 proceeded from only one machine, and were consequently 

 available for electro-deposition, or for any other purpose 

 for which a direct current might be required. 



Although this property of synchronous rotation has as 

 yet been observed only in the case of several pairs and a 

 triple combination of machines, yet there is no reason for 

 supposing that it may not be extended to anj'^ number of 

 machines that may be conveniently worked together from 

 the same prime mover. It is necessary, however, to observe 

 that as the controlling power of the current is only calcu- 

 lated to correct such minute deviations from synchronism 

 as it is beyond the power of mechanical skill to prevent, 

 the driving and driven pulleys should be respectively as 

 nearly as possible of the same diameters, as the correction 

 of any considerable difference in the number of the revolu- 

 tions of the armatures, caused by difi'erences in the dia- 

 meters of the pulleys, must necessarily be attended by a 

 corresponding diminution of the useful efiPect of the current 

 outside the machines. 



