130 Proceedings of Royal Society of Edinburgh. [sess. 
accurate ; but we see now that the more curious of them are com- 
paratively easily explained as being due to an initial twist in the 
wire of a few minutes per unit length. This is true not only of the 
average polarity acquired, but also of the asymmetrical form of the 
curve with reference to the line of zero field. For, as may be seen 
by a study of Ewing’s curves {e.g., Phil. Trans., plate lx. fig. 17, 
1885), such an asymmetry exists in a cyclic curve taken about a 
mean value of field other than zero. Now here we have a finite 
mean value of longitudinal intensity supported by the current along 
the wire. if, in the curves shown in the preliminary note, we shift 
the upper narrow graph to the right and the lower one to the left 
so that their mean points have abscissae equal to the longitudinal 
fields corresponding to their ordinates regarded as intensities, we 
shall see at once a sufficient reason for their asymmetrical form. 
All that can be safely said regarding the effect of a current along 
an iron or nickel wire, upon the susceptibility of the same to a 
longitudinal field, is that the susceptibility is markedly diminished, 
and that the residual magnetism* falls off more quickly than the 
total reduced magnetism. In other words, a current along a wire 
diminishes the hysteresis (to use Ewing’s word) relatively to a 
cyclically varying longitudinal field. The former conclusion agrees 
with the result obtained by Schultze (Wied. Ann., xxiv., 1885) 
in his experiments on the reciprocal action of mutually perpen- 
dicular magnetisms. He experimented with iron and steel tubes, 
and the circular magnetisation was induced by currents altogether 
outside the iron. He does not seem to have discussed the properties 
of cyclic magnetic graphs, or even the ratio of the residual to the 
total induced longitudinal magnetism, with or without the circular 
magnetism. It is therefore impossible at present to say whether 
the diminished hysteresis here noted is due to the magnetic effect 
of the current in the wire, or, as is perhaps more probable, to the 
direct vibratory action of the current upon the molecules, thereby 
accelerating the breaking up of unstable molecular groupings. 
* The experiments proving this are reserved, as not being quite completed. 
