424 Prof. J. A. Ewing on the supposed Helical Path of the 



In Prof. Hughes's experiments, magnetized iron or steel 

 wire was placed inside and along the axis of a coil which was 

 in circuit with a telephone. The coil could be turned about 

 an axis perpendicular to the wire. By means of the tele- 

 phone it was observed that, even when the wire was normal 

 to the plane of the coif, a series of currents were induced in 

 the coil when an intermittent current was made to pass along 

 the wire. By turning the plane of the coil round through a 

 certain angle, silence was restored in the telephone. This 

 result would, of course, be consistent with the hypothesis that 

 the path of the current in the wire is not rectilinear but 

 helical. 



But it is clear that the same inductive effects would be 

 given by changes in the longitudinal magnetization of the 

 wire accompanying the changes in the transmitted current. 



Weber's theory of magnetization, which assumes that the 

 molecules of iron or steel are always magnets, and that mag- 

 netization consists in bringing their axes into more or less 

 complete parallelism, implies that if magnetization exists in 

 one direction, then any supplementary magnetization at right 

 angles to that must produce a diminution of the first. The 

 degree to which the second magnetization affects the first will 

 depend on the nearness of the latter to its limiting value. If 

 it approaches that closely, then the second magnetization will 

 take place wholly at the expense of the first. Hence, when a 

 current traverses a longitudinally magnetized wire, the cir- 

 cular magnetization caused by the current must reduce the 

 original longitudinal magnetization. The first passage of the 

 current will produce a relatively large effect ; and subsequent 

 interruptions and renewals of it will cause fluctuations in the 

 value of the magnetic moment, whose external inductions will 

 be precisely the same as if the path of the traversing current 

 were a helix. 



The experiments of Prof. Hughes agree with this deduction 

 from "Weber's theory. A current entering at the nominal 

 N. pole gave an inductive effect corresponding to a right- 

 handed spiral ; entering at the S. pole, it gave an effect cor- 

 responding to a left-handed spiral. Hence the inductions 

 were in both cases of the kind which would be produced by a 

 diminution of the original magnetization of the wire. 



A second experiment consisted in passing a steady current 

 through the wire from N. to S., and superposing on it an 

 intermittent current. The inductive effects were then such 

 as would correspond to a right-handed spiral, both when the 

 direction of the intermittent current was the same as that of 

 the steady one and when their directions were opposite. From 



