142 DOVE ON THE ELECTRICITY OF INDUCTION. 



4. Induction exerted by the connecting wire of a Ley den jar 

 upon itself. 



55. This, to my knowledge, has never yet been experimentally 

 proved. It may however easily be done in the following manner : 

 — If m n (Plate I. fig. 5) represents the connecting wire of a Ley- 

 den jar, and a b the spiral portion of it, c h h d a secondary con- 

 nection which, by means of the handles h h, is effected through 

 the body, a shock is perceived at the moment a spai'k passes at 

 n ; this however is not the case when the secondary connexion 

 is made as represented in fig. 6, even when the distance from 

 h to h is precisely the same in both cases. In the former case 

 the spiral portion of the connecting wire is closed by the body 

 connecting h with h ; in the latter it is not so. If the shock 

 were produced by a division of the current, it must inevitably 

 occur in both cases. As this is not the case, it must be the 

 effect of a true induction. The power of the shock is increased 

 very perceptibly by a bundle of wires. A cylinder of nickel 4 

 inches long and 1^ inch thick was now inserted, without en- 

 abling me to ascertain in which direction the change was effected, 

 as the power of the shock rendered it comparatively small. 

 The insertion of a solid iron cylinder, however, materially 

 weakens the shock, as does also the insertion of a non-magnetic 

 metal. A closed secondary spiral surrounding the spiral portion 

 of the connecting wire considerably decreases the power of the 

 induction shock of the connecting wire, but very little however 

 when it is composed of two pieces un symmetrically joined. 

 With the calorific test a decrease is observed at the secondary 

 connexion on the insertion of iron in any form, but an increase 

 in the power of magnetizing a steel needle. The induction of 

 this extra current is therefore identical with that of the secondary 

 current in separate wires. 



5. Results of the experiments with electro-magnetized iron. 



56. If the I'esults which have been obtained by magnetizing: 

 iron with electricity from different sources be collected into one 

 general view, we find that — 



a. Iron in the form of solid rods, of entire or longitudinally 

 cut tubes, of insulated bundles of wires with or without con- 



