DOVE ON THE ELECTRICITY OF INDUCTION. 129 



6. Experiments with piles of iron discs, and with cylinders of 

 iron filings. 



34. As the division of an iron cylinder by longitudinal sections 

 parallel to the axis hinders the formation of peripherical electri- 

 cal currents, without interfering with the production of magnetic 

 polarity, so, on the contrary, the powerful development of mag- 

 netic polarity is prevented by cross sections at right angles to 

 the axis, whilst the production of peripherical electrical currents 

 is in no way retarded. A column of iron discs arranged with 

 discs of paper between them can therefore affect a galvanometer 

 but slightly, on account of its small amount of magnetic polarity ; 

 and from the facility with which electrical currents are excited 

 in it, its physiological action must also be but slight, as the ex- 

 periments have shown. With a pile of iron filings, the excita- 

 tion of electrical currents is at the same time hindered on ac- 

 count of the longitudinal separation ; it will therefore exert a 

 weak, though proportionally more powerful physiological action 

 than the column of discs. This is confirmed by the experiments 

 in the former series (13). 



35. The whole of the foregoing experiments lead to the result, 

 that the metallic case surrounding the wire bundle (or, as is the 

 case with a solid iron cylinder, the conducting metallic sur- 

 face, combining all the single wires into one metallic whole) does 

 not weaken the current induced by it, but only retards it, i. e. it 

 spreads over a longer time the neutralization of the quantity of 

 electricity set in motion by the evanescent magnetism in the en- 

 closing wire, without decreasing the quantity itself. This retar- 

 dation has no influence upon the magnetic needle, which adds 

 together the effects of the current, in which case it is quite im- 

 material how long this addition lasts. The removal of the me- 

 tallic case, or the frequent repetition of the interruption to me- 

 tallic continuity, is to be compared to the accelerated motion 

 produced by an inductor enclosing a magnet, which increases 

 its physiological action without adding to the galvanometric 

 effect. 



7. Shock and sparks on breaking the circuit by means 0/' spirals 

 and electro-magnets. 



When the view deduced from the simultaneous considera- 



VOL. V. PAKT XVII. K 



