MAGNETISM. - Since remote antiquity it had been observed that certain iron minerals possess the singular property that, when pieces of them are brought near one another, they may attract or repel each other according to their relative orientation. The Greeks called such pieces "magnets" and their property "magnetism." In less remote times it was also observed that magnets always attract any iron object, and that pieces of iron, or rather of tempered steel, when rubbed against them, themselves acquire that property with greater or lesser intensity. Hence the former were called "natural magnets" and the latter "artificial magnets."
The observation that magnets suitably suspended tend to orient themselves along a determinate direction led to the construction of the compass, using artificial magnets in the form of a needle, and to its use in navigation. While the Chinese claim to have used compasses as far back as ca. 1000 B.C., in Europe they spread widely only in the 13th century. In the centuries immediately following, the compass was used rather empirically and its operation was erroneously interpreted. Columbus, who although from 1492, in the vicinity of the Island of Iron, had observed that the compass needle deviated from the meridian by a few degrees toward the west, whereas in Europe it deviated on the contrary toward the east, and had therefore discovered the magnetic declination varying from place to place, still thought, along with the scientists of his time, that the behavior of the magnetic needle was determined by an attractive center in the sky.
Only W. Gilbert (1540-1603), after a remarkable series of observations, arrived at the correct conviction that the earth participates in magnetic phenomena as a gigantic magnet, and he constructed a model of it, his terrella, a large magnet of spherical shape by means of which he succeeded in experimentally interpreting the known fact that the inclination of magnetic needles vanishes at the equator and is greatest in the vicinity of the magnetic poles, which however he supposed to coincide with the geographic poles; this prevented him from an exact interpretation of declination. His results were published in 1600.
From then until the end of the following century, further studies were directed toward terrestrial magnetism, the localization of its poles, and the technique of instruments; matters undoubtedly of great practical interest, but of limited interest for the physical knowledge of nature. However, when Coulomb, after the discovery of his well-known law of attraction and repulsion of electric masses, arrived at the analogous law for the poles of long thread-like magnets, also of the same purely Newtonian type, magnetism was conceived as constituted by magnetic masses acting at a distance upon one another like electric masses and material masses; magnetism was then considered, like matter and electricity, one of the fundamental constituents of the universe, according to the mechanistic criterion then prevailing.
But precisely through new magnetic discoveries, after a little more than two decades, the mechanistic criterion of physics was to receive its first grave refutation from Oersted's discovery of the action of the electric current on magnetic poles; an action which, by its direction, stands in clear contrast with the said criterion. The subsequent construction of electromagnets, even consisting of a simple conductor wound into a helix and traversed by an electric current, clearly showed that to obtain the known magnetic effects it was by no means necessary to resort to hypothetical permanent magnetic masses, but that electricity in motion sufficed. Thus it was that, on the initiative of Ampère, magnetism itself, in both natural and artificial permanent magnets, came to be interpreted as resulting from innumerable microscopic electromagnets, each constituted by microscopic electric currents or rather, in more modern terms, by innumerable electrons rotating within the material of the magnet. Thus in the final analysis the study of magnetism was totally absorbed by electrology.