DOVE ON THE ELECTRICITY OF INDUCTION. 139 



on the contrary, the inducing action is greater when this iron is 

 used in the form of a bundle of wire. 



49. A bundle of insulated iron wire, however, which is sur- 

 rounded by an entire tube of brass, has the same action as a 

 solid iron cylinder, i. e. it weakens the shock of its spiral, and 

 a current is produced proceeding from the empty spiral. The 

 same is the case when it is surrounded by a spiral of copper wire 

 coiled throughout in the same direction, and connected at the 

 ends. It also shows a weakening action, though this is but 

 very slight, when this spiral is a bad conductor, composed of 

 German silver for instance ; and it is not impossible that, with a 

 greater number of wires in its interior, and a thinner spiral wire, 

 the action might be produced in a contrary direction. A spiral 

 formed of a doubled copper wire with connected ends, is likewise 

 here without effect, for a bundle of wire enclosed within such a 

 spiral retains in equilibrium an unenclosed bundle of wire in the 

 other tube. 



50. A solid rod of nickel produces hardly a perceptible 

 physiological action with compensated spirals. The current 

 produced by it, however, tested by the condenser and the re- 

 sinous figures, proceeds from the spiral in which it is placed. 

 Solid nickel, therefore, increases the inducing action, whilst 

 solid iron decreases it. The previously existing polarity of the 

 nickel has likewise no effect upon it, for the direction of the cur- 

 rent remains the same when an opposite position is given to the 

 bar of nickel in relation to its spiral. With varnished nickel 

 wires we may therefore expect a still more marked increase of 

 power. 



51. All the facts here established are independent of the rela- 

 tive position of the connecting spiral, the secondary spiral, and 

 of the cylinder to each other; for they were obtained in the 

 same manner when the battery was discharged through the outer 

 spirals, and the induction tested upon the inner spirals. 



52. To ascertain whether a rod placed in one of the tubes in- 

 creases the physiological action, iron wires may be placed in the 

 other tube until equilibrium is again established, whilst in the 

 case of the inserted rod decreasing the action, the disturbed equi- 

 librium must be restored by the insertion of wires of a non-mag- 

 netic metal, such as brass. Thin wires must be chosen for such 

 testing experiments ; for, as a single wire may be considered as a 



