On Ellectro-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. Whena 
current from a single battery of thirty five feet of zine 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 
ame 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 
tiband, with the battery above mentioned, becomes strongly mag- 
hetic. 
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 amusante, 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 
tooms. 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. 
52. 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 th duct parated to the 
Femarkable distance of six feet eight inches. 
