Contemporary Advances in Physics-XIII. Ferromagnetism

magnetism are well explained by the contemporary theory, many seem admirably clear; but none of these was or could have been witnessed by the Greeks. We know much about the magnetic properties of gases, dilute solutions, free atoms, elements and compounds which are so feebly magnetizable that before 1830 they were not supposed to be " m a g n e t i c " at all; we are still perplexed by the behaviour of iron and lodestone. This is the reason why there are textbooks of magnetism, in which hundreds of pages are devoted to the data and the theories of a number of effects most difficult to perceive and known to none but physicists, while the magnets of daily experience are dismissed with a chapter or two of mere description. As for electrified amber and its kindred, they are fortunate to have a few paragraphs of any modern treatise on electricity bestowed upon them. Frictional electricity is not a very striking phenomenon, nor is it valuable in engineering; consequently it has been allowed to slip into obscurity, shunned by cautious students on the hunt for problems promising immediate returns. Ferromagnetism is not so unobtrusive. Much of the electric machinery which has transformed the world since Napoleon derives all its efficacy from certain blocks of iron or magnetizable alloy, enmeshed among the wires. So useful a property of matter does not consent to lie neglected; physicists are forced to hearken to its insistent demands for attention. Ambition to achieve some technical advance supplies a strong incentive; and there is a feeling of humiliation that a quality of matter so conspicuous and so remarkable, and so remarkably limited to a particular class of substances not in other ways exceptional, should not be properly connected with the structure of contemporary physics.