384 



PROCEEDINGS OF THE AMERICAN ACADEMY 



It will be seen by the above tables that the difference of potential is 

 more than doubled by the application of the armature. These experi- 

 ments were conducted with solid cores, on account of the ditficulty, 

 with the means at my immediate command, of making the ends of 

 bundles of iron wire sufficiently plane. Experiments were next made 

 to determine the influence of the size of the armature. The following 

 table shows the results : — 



TABLE II. 



The mass of the armature, therefore, appeared to make no difference. 

 Experiments speedily showed, however, that the induced currents were 

 affected by the amount of bearing surflice of the armature and the dis- 

 position of its mass between the two poles of the electro-magnet 

 of the horseshoe on which the primary coil was placed. There is 

 no doubt that the core of the electro-magnet should consist of small 

 iron wires, as in the ordinary Ruhmkorf coil. The iron core, with the 

 armature, would then be in the form of a hollow square, one side of 

 which is made up of a bundle of fine iron wires, and the remaining 

 three equal sides constitute the armature. It appears from the above 

 inv-estigation that we can reduce the expense of the present form of 

 induction coil, for a much less number of winding of fine wire will be 

 needed when an armature is employed, to produce the same strength 

 of induced currents that are produced in straight electro-magnets with- 

 out armatures. 



