In 1885 it was shown by Bidwell, in the first of a series of papers on the subject, that if the magnetizing force is pushed beyond the point at which Joule discontinued his experiments, the extension of the bar does not remain unchanged, but becomes gradually less and less, until the bar, after first returning to its original length, ultimately becomes actually shorter than when in the unmagnetized condition.
Thomson (Lord Kelvin), who in 1856 announced that magnetization rendered iron and steel positive to the unmagnetized metals.'
Nickel when magnetized is always positive to the unmagnetized metal.
In the case of cobalt no such relation could be traced; it appeared that the thermo-electric power of the unmagnetized with respect.
[[[Feebly Susceptible Substances]] different specimens were tested, all of which became, like iron, thermo-electrically positive to the unmagnetized metals.