The alterations brought about in the magnetic moments of magnets, composed of various metals and alloys, by alternate cooling and warming between ordinary room temperature and that of liquid air have been very fully investigated by Dewar and Fleming. It was found by these experimenters that in the case of most of the metals examined the effect of the first cooling upon the magnet—which had previously been magnetised to saturation in the field of an electromagnet—was to bring about a very considerable reduction in its magnetic moment. On allowing the magnet to warm to room temperature its magnetic moment still further diminished. On cooling once more to the liquid air temperature the magnetic moment increased, and from and after this stage it was found that the magnetic moment of the magnet when cold exceeded that of the magnet when at room temperature by a definite amount. The changes brought about by the treatment were found to be much greater in the annealed than in the quenched condition of the material.