1838] WRITINGS OP JOSEPH HENRY. 121 



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 ribbon, with the battery above mentioned, 

 becomes strongly magnetic. 



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

 munication that the induction at a distance affords the means 

 of exhibiting 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 some- 

 what connected with the experiments to be described in the 

 next section, and which exhibits the action in a striking 

 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 adjoining 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 produced 

 through a door, or thin wooden partition. 



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

 graduating the intensity of the shock in the case of its appli- 

 cation to medical purposes. The helix may be suspended 

 by a string passing over a pulley, and then gradually low- 

 ered 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 conductors enables us to imitate, in a very striking 

 manner the inductive operation of the magneto-electrical 

 machine, by means of an uninterrupted galvanic current. 

 For this purpose it is only necessary to arrange two coils to 

 represent the two poles of a horseshoe magnet, and to cause 

 two helices to revolve past them in a parallel plane. While 

 a constant current is passing through each coil, in opposite 



