DOVE ON THE ELECTRICITY OF INDUCTION. 12/ 



With an increase of thickness therefore in the iron case, the 

 action as measured by the galvanometer is lessened, and a me- 

 chanical division of the tubes by cutting has no very marked in- 

 fluence. But cutting the tubes even when the metal is thin 

 produces an increase, although but small, in the physiological 

 action. Lastly, the physiological action of the wires in a tube 

 of sheet iron is proportionally small, but it is greater when the 

 tubes are cut open than when they are entire. If, for instance, 

 physiological equilibrium has been established by any means be- 

 tween an entire and a cut tube, this will be destroyed when 

 equally powerful bundles of wires are placed in both tubes, and 

 the shock proceeds from the cut tube. 



5. Experiment with closed and unclosed conducting cases 

 containing bundles of wire. 



31. Of two bundles of wires which compensated each other, 

 one was placed without any case in the wooden tube of the mag- 

 netizing spiral, the other enclosed in a tube of cardboard, round 

 which was wound in more than 200 coils of copper wire covered 

 with silk, so that the coils surrounded the bundle of wire 

 throughout its whole length. The projecting ends of this 

 spiral, which, to distinguish it from the magnetizing spiral 

 connected with the battery, and from the induction-spirals sur- 

 rounding the former, and connected by the human body or the 

 galvanometer, we may call the enclosing spiral, could be con- 

 nected by a clamp, or, to exhibit the secondary current in- 

 duced in them, by a galvanometer. There were four such card- 

 board cases ; the spiral in one of them was right-handed, in the 

 second left-handed, in the third half right-handed, half left- 

 handed ; in the fourth it was made up of a wire folded and then 

 twisted, and might therefore be considered as composed of two 

 spirals wound in the same dii'ection but unsymmetrically con- 

 nected. The two last spirals were without action, both when 

 their ends were or were not joined, not however the two first ; 

 whence it directly follows, that the effect produced by these must 

 be ascribed to an electric current, which in the tw'o latter was 

 divided into two halves that mutually destroyed each other. 

 Suppose the action of the bundle of iron wires replaced by that 

 of an electro-dynamic solenoid, it is easy to perceive that its 

 coils would run nearly parallel with the close coils of the en- 

 closing spiral, whether the latter be wound in a like or in an 



