106 MR. H. WILDE ON A PROPERTY OF 



long and J- of an inch in diameter. The currents were 

 taken from the armatures by means of copper brushes 

 rubbing against metal rings connected respectively with 

 the ends of the armature-coils, and were therefore in alter- 

 nate directions. It has been found that alternating cur- 

 rents are much better adapted for the production of a 

 constant electric light at a fixed point in space than the 

 current which has been rectified by means of a commu- 

 tator. 



The clutch; by which the armatures were connected, 

 consisted of two iron disks about 4 inches in diameter, 

 having, in the face of one, two iron pins which could be 

 guided into two corresponding holes in the face of the other. 

 These disks could be engaged or disengaged either when 

 the machines were at rest or in motion. The relative 

 positions of the pins and holes in the disks were such that 

 the armatures might be engaged in reversed positions of 

 half a revolution when required. 



Each of these 4-inch machines, when making about 

 2000 revolutions per minute, was of itself capable of pro- 

 ducing a very efficient electric light ; and when the two 

 armatures were clutched together in such a position that 

 the united positive currents from both machines proceeded 

 from one polar terminal simultaneously with the united 

 negative currents from the other polar terminal, the sum 

 of the currents of the two machines was obtained. On 

 the other hand, when the armatures were clutched together 

 in the reverse position without any change being made in 

 the armature connexions^ no current was produced outside 

 the two machines. 



These experiments, besides exhibiting the necessity of 

 synchronous rotation, further showed that the armatures 

 must also occupy the same relative position in the magnet- 

 cylinders in order that the combined current from the two 



