NOTES AND APPENDICES. 



NOTE A. 



ON THE INDUCTIVE ACTIONS IN THE NEW DYNAMO- 

 ELECTRIC MACHINES. 



THE inductive actions resulting from the relative move- 

 ments of the inducing and induced circuits are seldom studied 

 with exactitude, and on that account very inaccurate theories 

 of several recently invented dynamo-electric machines have 

 been put forward. The following series of experiments may 

 serve to fix our ideas on the subject : 



Let us suppose that on a powerful straight magnet are 

 wound several spires of an insulated wire, the ends of which 

 are connected with a distant galvanometer, and let the coil 

 so formed be capable of taking different positions on the 

 magnet. If this coil is placed at the south pole of the 

 magnet, and a soft iron armature is brought near that pole, 

 a current will be obtained corresponding in duration with a 

 magnetizing current, for it results from the increase of mag- 

 netic energy communicated to the bar by the presence of the 

 armature. This current will give a deviation of 12 degrees 

 to the right, and on withdrawing the armature we shall have 

 a second deviation of 12 degrees to the left. Therefore, in 

 the following experiments a deviation to the right will repre- 

 sent inverse currents, and a deviation to the left, direct cur- 

 rents.* Let us now see what will happen from the various 



' :> It should be observed that the direction of the currents due to the in- 

 crease or diminution of magnetic intensity is always the same, whether 



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