172 DOVE ON THE ELECTRICITY OF INDUCTION. 



last, because the transversely connected secondary spirals per- 

 formed the part of an unconnected spu-al. 



74. The ■weakening effect produced by the insertion of the 

 extra spiral filled with iron has a threefold cause. The current 

 circulating in the \vire coils of the surrounded keeper before 

 connexion is broken by the spring, traverses also the coils of the 

 extra spiral, by which means it experiences a greater resistance 

 to conduction. If the inserted spiral has the same length of 

 wire as the coil of the keeper, which is here the case, then the 

 resistance is five times as great when the hand is arranged for 

 physical effects. The shock which is produced on breaking 

 the closed circuit is therefore perceptibly diminished even when 

 the wire of the spiral is stretched out straight. But the coils 

 of this spiral now exert an inducing action upon each other, 

 as does also the incipient magnetism in the inserted iron. The 

 incipient extra current thus produced in the wire of the extra 

 spiral increases therefore the action of the augmented resist- 

 ance to conduction, and it is evident that, as these causes act in 

 the same direction, an addition to the number of the extra spirals 

 must constantly increase this action. This occm's indeed in so 

 palpable a manner, that, when five spirals having 2000 feet 

 length of wire wei'e inserted together, and iron was placed with- 

 in them, the shocks at last almost entirely disappeared. 



75. If connexion is made by II and III (E), in which case 

 the empty extra spiral alone remains in the circuit, then more 

 powerful shocks are obtained when the hand of the pachytrope 

 is arranged for physical, than when it is arranged for physiologi- 

 cal effects. The insertion of unenclosed bundles of wire and 

 tubes of sheet iron very much increases the shock. This increase 

 is less Avith iron bundles of wire in entire tubes, with solid 

 iron, steel, cast iron and nickel. With the unmagnetic metals 

 the change was too slight to enable us to say in which direction 

 it occurred. If the exti-a spiral, enclosing a bundle of iron wire, 

 is surrounded with the secondary spiral mentioned at 73), then 

 the very powerful shocks obtained from the handles II and III 

 with an unconnected secondary spiral are very much weakened 

 as soon as thi? secondary spiral is closed by means of metal. 

 When two extra spirals were inserted into two secondary spirals, 

 with a transverse connexion of the former, the shocks from the 

 handles II and III were powerful, but they were weakened by a 



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