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PROCEEDINGS OF THE AMERICAN ACADEMY 



increases from both ends towards the middle (which was shown to 

 be the case by Jacobi and Lenz in 1844) ; and when the armature is 

 applied, the curves diverge greatly near the pole upon which the 

 armature is placed. 



Our next experiments were tried with a solid horseshoe-shaped 

 electro-magnet, the limbs of which were 12 cm. long, 2.5 cm. in diam- 

 eter ; the resistance of the electro-magnet was about .01 of an ohm and 

 that of the induction coil 1 ohm. 



TABLE II. 



The scale runs, increasing, from the bend of the electro-magnet to 

 the pole of the limb on which the induction coil was slipped. Here 

 there is a marked increase, resulting from the use of the armature, 

 which is shown in a striking manner by expressing the above results 

 as curves. The results of our experiments show : — 



1st. The application of an armature to one pole of a straight electro- 

 magnet results in an increase of the magnetic condition of the magnet. 



2d. The application of an armature to both poles of a horseshoe- 

 shaped magnet results in a remarkable increase of its magnetic state, 

 which increase is much the greatest near the armature. 



