76 WRITINGS OP JOSEPH HENRY. [1832 



of the magnetic action in one, and the sudden cessation of 

 it in the other. 



This experiment illustrates most strikingly the reciprocal 

 action of the two principles of electricity and magnetism, if 

 indeed it does not establish their absolute identity. In the 

 first place, magnetism is developed in the soft iron of the 

 galvanic magnet by the action of the currents of electricity 

 from the battery, and secondly the armature, rendered mag- 

 netic by contact with the poles of the magnet, induces in its 

 turn currents of electricity in the helix which surrounds it; 

 we have thus as it were electricity converted into magnetism 

 and this magnetism again into electricity. 



Another fact was observed which is somewhat interesting 

 inasmuch as it serves in some respects to generalize the 

 phenomena. After the battery had been withdrawn from 

 the acid, and the needle of the galvanometer suffered to 

 come to a state of rest after the resulting deflection, it was 

 again deflected in the same direction by partially detaching 

 the armature from the poles of the magnet to which it con- 

 tinued to adhere from the action of the residual magnetism, 

 and in this way, a series of deflections, all in the same direc- 

 tion, was produced by merely slipping off the armature by 

 degrees until the contact was entirely broken. The following 

 extract from the register of the experiments exhibits the 

 relative deflections observed in one experiment of this kind. 



At the instant of immersion of the battery, deflection 40° west. 



" " emersion " " " 18° east. 



Armature partially detached, " 7° east. 



Armature entirely detached, " 12° east. 



The effect was reversed in another experiment, in which 

 the needle was turned to the west in a series of deflections 

 by dipping the battery but a small distance into the acid at 

 first and afterwards immersing it by degrees. 



From the foregoing facts, it appears that a current of elec- 

 tricity is produced, for an instant, in a helix of copper wire 

 surrounding a piece of soft iron whenever magnetism is in- 

 duced in the iron ; and a current in an opposite direction 

 when the magnetic action ceases; also that an instantaneous 

 current in one or the other direction accompanies every 

 change in the magnetic intensity of the iron. 



