On Electro-Dynamic Induction. 221 



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 approximated, 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 in- 

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

 surprisingly great. A cylinder of soft iron, two inches in diame- 

 ter and one foot long, placed in the centre of the ring of copper 

 riband, with the battery above mentioned, becomes strongly mag- 

 netic. 



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

 nication, that the induction at a distance affords the means of ex- 

 hibiting some of the most astonishing experiments, in the line of 

 physique amusanie, to be found perhaps in the whole course of 

 science. I will mention one which is somewhat connected with 

 the experiments to be described in the next section, and which 

 exhibits the action in a striking manner. This consists in caus- 

 ing 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 adjoining one receives the 

 shock, by grasping the handles of a 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 produced 

 through a door, or thin wooden partition. 



62. The action at a distance affords a simple method of grad- 

 uating the intensity of the shock in the case of its application to 

 medical purposes. The helix may be suspended by a string pass- 

 ing 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. 



* Since writing the above, this distance has been much increased by using a 

 compound battery of eight elements, each of the above size ; with this, shocks 

 through the tongue have been obtained, when the conductors were separated to the 

 remarkable distance of six feet eight inches. 



