256 Prof. J. Henry's Contributions 



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 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. 



52. 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 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 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 

 directions, the effect of the rotation of the helices is precisely 

 the same as that of the revolving armature in the machine. 



54-. A remarkable fact should here be noted in reference to 

 helix Ko. 4, which is connected with a subsequent part of the 

 investigation. This helix is formed of copper wire, the spires 

 of which are insulated by a coating of cement instead of 

 thread, as in the case of the others. After being used in 

 the above experiments, a small discharge from a Leyden jar 

 was passed through it, and on applying it again to the coil, 

 I was much surprised to find that scarcely any signs of a 

 secondary current could be obtained. 



55. The discharge had destroyed the insulation in some 

 part, but this was not sufficient to prevent the magnetizing of 

 a bar of iron introduced into the opening at the centre. The 

 effect appeared to be confined to the inductive action. The 

 same accident had before happened to another coil of nearly 

 the same kind. It was therefore noted as one of some im- 

 portance. An explanation was afterwards found in a peculiar 

 jiction of the secondary current. 



