130 DOVE ON THE ELECTRICITY OF INDUCTION, 



tion of the galvanometric and physiological effects, that the 

 increase of the latter on breaking up a sohd iron rod into a 

 bundle of wires is to be ascribed to an acceleration of the current, 

 not to an augmentation of the quantity of electricity set in mo- 

 tion, is to be applied to explain the phaenomena of that depart- 

 ment within which the physiological effects only can be sub- 

 mitted to an accurate investigation, and not the galvanome- 

 tric effects, the application can only be warranted by a com- 

 plete parallelism of the physiological phaenomena in both de- 

 partments. Now the physiological action of the extra current 

 is already made known by the experiments of Sturgeon* and 

 Magnusf, and is analogous to that of the secondary current 

 which we have been examining, for the former has shown that 

 the shock on breaking a galvanic circuit is stronger when, instead 

 of a solid iron cylinder, a bundle of iron ivires is introduced 

 into the spiral forming the connecting wire ; the latter, on the 

 other hand, that the power of this shock is diminished w hen the 

 bundle of wire is enclosed in an entire conducting case. I there- 

 fore only subjoin a few experiments, which show that it is not 

 necessary for the metallic case to separate the bundle from the 

 connecting wire, but that the same phaenomena occur when this 

 case surrounds externally the wire electro-magnet, and that 

 spirals are just as effective as cases, whence it is rendered more 

 obvious that the retarding cause is referable to an induced electric 

 current. 



36. Spirals of insulated copper wire were wound round bun- 

 dles consisting of from twenty-five to fifty iron wires, and with 

 the electro-magnet thus formed and others formed of solid iron, 

 a galvanic circuit was closed by means of handles. On breaking 

 the circuit a brilliant radiating spark appeared, and a consider- 

 able shock. The electro-magnets formed from the bundles of 

 wires were now inserted in an entire brass tube. The shocks 

 almost entirely disappeared, and the spark was very slight. 

 The brass tube cut longitudinally, however, produced no change 

 in the action of the electro-magnet ; the spark retained its great 

 brilliancy, and the shocks their former power. 



The same results were obtained with the entire and cut gun- 

 barrel when they surrounded the electro-magnetized bundle of 

 wires, with this difference only, that in the entire gun- barrel a 

 * Annals of Electricity, i. p. 481. f Pogg. Ann. xlviii. p. 95. 



