If one pole of the bar-magnet is brought near the compass, it will attract the opposite pole of the compass-needle; and the magnetic action will not be sensibly affected by the interposition between the bar and the compass of any substance whatever except iron or other magnetizable metal.
When the magnetic induction flows through a piece of iron or other magnetizable substance placed near the magnet, a south pole is developed where the flux enters and a north pole where it leaves the substance.
It is to the non-uniformity of the field surrounding a magnet that the apparent attraction between a magnet and a magnetizable body such as iron is ultimately due.
According to this theory the molecules of any magnetizable substance are little permanent magnets the axes of which are, under ordinary conditions, disposed in all possible directions indifferently.
Ordinary magnetizable iron is in many respects an essentially different substance from the non-magnetizable metal into which it is transformed when its temperature is raised above a certain point.
An alloy containing about 3 parts of iron and I of nickel - both strongly magnetic metals - is under ordinary conditions practically non-magnetizable (1 1=1'4 for any value of H).
But if the alloy is heated up to 580° C. it loses its susceptibility - rather suddenly when H is weak, more gradually when H is strong - and remains non-magnetizable till it is once more cooled down below the freezing-point.
This material can therefore exist in either of two perfectly stable conditions, in one of which it is magnetizable, while in the other it is not.
Magnetizable it is a hard steel, having a specific electrical resistance of o 000052; when non-magnetizable it is an extremely soft, mild steel, and its specific resistance is 0 000072.
Certain non-magnetizable alloys of nickel, chromium-nickel and chromium-manganese were rendered magnetizable by annealing.
The following table gives the exact composition of some alloys which were found to be non-magnetizable, or nearly so, in a field of 320.
Heusler 2 in 1903 that certain alloys of the non-magnetic metal manganese with other non-magnetic substances were strongly magnetizable, their susceptibility being in some cases equal to that of cast iron.
The metals used in different combinations included tin, aluminium, arsenic, antimony, bismuth and boron; each of these, when united in certain proportions with manganese, together with a larger quantity of copper (which appears to serve merely as a menstruum), constituted a magnetizable alloy.
In all such magnetizable alloys the presence of manganese appears to be essential, and there can be little doubt that the magnetic quality of the mixtures is derived solely from this component.
Guillaume 6 explains the ferromagnetism of Heusler's alloy by supposing that the naturally low critical temperature of the manganese contained in it is greatly raised by the admixture of another appropriate metal, such as aluminium or tin; thus the alloy as a whole becomes magnetizable at the ordinary temperature.
A magnetizable substance was supposed to consist of an indefinite number of spherical particles, each containing equivalent quantities of the two fluids, which could move freely within a particle, but could never pass from one particle to another.