VII. On the changes produced by magnetisation in the dimensions of rings and rods of iron and of some other metals

Abstract

In a paper communicated to the Royal Society in 1885 I described some effects of magnetisation upon the dimensions of iron rods. It was there shown that the elongation which such a rod at first undergoes when magnetised (a phenomenon which had been carefully studied by Joule and others) does not, as had been believed, remain unchanged at a maximum when the magnetising force exceeds that which is sufficient to produce so-called saturation. On the contrary, it is found that, when the magnetising force is continually increased beyond this limit, the elongation becomes gradually less until the rod is at last actually shorter than it was in the unmagnetised condition. Though there could be little doubt as to the general qualitative reality of the effects described, the experimental evidence was nevertheless not free from certain defects which I -was not at the time able to overcome.