ON ELECTRO-DYNAMIC INDUCTION. 315 



49. The action at a distance was still further increased by coiling 

 the long wire of the large spool into the form of a ring of four feet 

 in diameter, and placing parallel to this another ring, formed of the 

 four ribands of coils No. 1, 2, 3 and 4. When a current from a single 

 battery of thirty-five feet of zinc surface was passed through the riband 

 conductor, shocks through the tongue were felt when the rings were 

 separated to the distance of four feet. As the conductors were ap- 

 proximated, the shocks became more and more severe; and when at 

 the distance of twelve inches, they could not be taken through the 

 body. 



50. It may be stated in this connection, that the galvanic induction 

 of magnetism in soft iron, in reference to distance, is also surprisingly 

 great. A cylinder of soft iron, two inches in diameter and one foot 

 long, placed in the centre of the ring of copper riband, with the bat- 

 tery above mentioned, becomes strongly magnetic. 



51. I may perhaps be excused for mentioning in this communica- 

 tion that the induction at a distance affords the means of exhibiting 

 some of the most astonishing experiments, in the line oi physique amu- 

 sante, to be found perhaps in the whole course of science. I will men- 

 tion one which is somewhat connected with the experiments to be 

 described in the next section, and which exhibits the action in a strik- 

 ing manner. This consists in causing the induction to take place 

 through the partition wall of two rooms. For this purpose coil No. 1 

 is suspended against the wall in one room, while a person in the ad- 

 joining one receives the shock, by grasping the handles of the helix, 

 and approaching it to the spot opposite to which the coil is suspended. 

 The effect is as if by magic, without a visible cause. It is best pro- 

 duced through a door, or thin wooden partition. 



52. The action at a distance affords a simple method of graduating 

 the intensity of the shock in the case of its application to medical pur- 

 poses. The helix may be suspended by a string passing over a pulley, 

 and then gradually lowered down towards the plane of the coil, until 

 the shocks are of the required intensity. At the request of a medical 

 friend, I have lately administered the induced current precisely in this 

 way, in a case of paralysis of a part of the nerves of the face. 



53. I may also mention that the energetic action of the spiral con- 



VI. — 4 D 



