DOVE OX THE ELECTRICITY OF INDUCTION. 119 



titatively determining the relative value of the two opposing cur- 

 rents. Gray iron from the crucible furnace overpowered con- 

 siderably both soft and hard steel. Very hard white iron from 

 the cupola furnace with cold blast comes veiy near in its action 

 to soft steel, but very perceptibly exceeds that of hard steel. 

 The difference between malleable and cast iron was less than 

 that between malleable iron and steel, and indeed with some 

 kinds of cast iron the difference was so slight that it could not 

 be accurately determined by the method of drawing out the bars. 



18. From these expei'iments, and from those made with bun- 

 dles of wires, it follows that the series obtained by the galvano- 

 meter for the different kinds of iron compared, is a different one 

 to that obtained by physiological means. 



The physiological action is therefore dependent on the one 

 hand upon the mechanical discoatinidty of the mass, and on the 

 other upon the peculiar nature of the iron. Hence it follows, 

 that wires of soft iron ha\-ing a different diameter may compen- 

 sate a cylinder of a particular kind of iron both as regards the 

 magnetic needle and sensation at the same time. This was the 

 case, for instance, with twelve wires 267 lines in diameter, and a 

 cylinder of gray iron from the crucible furnace. The influence 

 exerted by the peculiar nature of the kind of iron is also mani- 

 fest from the following facts : — When the cylinder is of hardened 

 steel, no difference is perceptible between the induction shock 

 produced by the polarization of the cylinder when the circuit is 

 closed, and the shock produced by its depolarization when the cir- 

 cuit is broken ; the difference between the shocks is perceptible 

 if the cylinder is composed of soft iron, much more so with cast 

 iron cylinders or bundles of wires, when the shock on breaking 

 the circuit is more intense than that produced by closing it. 

 This difference depends more upon the nature of the iron than 

 upon its mechanical discontinuity, for it was found to be greater 

 with eleven soft iron wires than with fifteen hard steel wires, 

 which, when opposed to each other, destroyed each other's phy- 

 siological action. 



19. From all the experiments which have as yet been insti- 

 tuted, it appears that gray iron approaches the nearest in its in- 

 ducing action to the bundle of wires, for its physiological action 

 is proportionally greater than could have been expected from the 

 intensity of the current determined by the galvanometer. The 

 inducing powers of gray pig iron lead therefore to the supposi- 



