1838] WRITINGS OF JOSEPH HENRY. 119 



to give only the general conditions which influence the gal- 

 vanic induction. To establish the law would require a great 

 number of more refined experiments, and the consideration 

 of several circumstances which would affect the results, such 

 as the conduction of the wires, the constant state of the bat- 

 tery, the method of breaking the circuit with perfect regu- 

 larity, and also more perfect means than we now possess of 

 measuring the amount of the inductive action; all these 

 circumstances render the problem very complex. 



SECTION III. 



On the Induction of Secondary Currents at a distance. 



45. In the experiments given in the two preceding Sections, 

 the conductor which received the induction, was separated 

 from that which transmitted the primary current by the 

 thickness only of a pane of glass ; but the action from this 

 arrangement was so energetic, that I was naturally led to 

 try the effect at a greater distance. 



46. For this purpose coil No. 1 was formed into a ring of 

 about two feet in diameter, and helix No. 4 placed as is shown 



YiQ. 4. — a represents helix No. 4, b coil No. 1 , in the form of a ring. 



in the figure. When the helix was at the distance of about 

 sixteen inches from the middle of the plane of the ring, 

 shocks could be perceived through the tongue, and these 

 rapidly increased in intensity as the helix was lowered, and 

 when it reached the plane of the ring they were quite severe. 

 The effect however was still greater, when the helix was 



