MAGNETISMO. — From remote antiquity it was observed that certain iron minerals possess the singular property that pieces of them, when brought near one another, may, depending on their relative orientation, either attract or repel each other. The Greeks called these pieces “magnets” and their property “m.” 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, likewise acquire that property to a greater or lesser degree. The former were therefore called “natural magnets” and the latter “artificial magnets.”
The observation that suitably suspended magnets tend to orient themselves in a definite 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 early as ca. 1000 B.C., in Europe they became widespread only in the thirteenth century. In the immediately following centuries the compass was used rather empirically and its operation was incorrectly interpreted. C. Colombo, who as early as 1492, in the vicinity of the Island of El Hierro, had observed that the compass needle deviated from the meridian by several degrees toward the west, whereas in Europe it deviated toward the east, and had thus discovered the magnetic declination, which varies from place to place, still believed, along with the scientists of his time, that the behavior of the magnetic needle was determined by an attracting center in the heavens.
Only G. Gilbert (1540–1603), after a notable series of observations, arrived at the correct conviction that the earth intervenes in magnetic phenomena as a gigantic magnet, and constructed a model of it, his terrella, a large spherical magnet by means of which he succeeded in experimentally interpreting the known fact that the inclination of magnetic needles vanished at the equator and was greatest in the vicinity of the magnetic poles, which, however, he assumed to coincide with the geographical poles; this prevented him from correctly interpreting the declination. His results were published in 1600.
From then until the end of the following century, further studies were directed toward terrestrial m., the localization of its poles, and the technique of instruments: matters undoubtedly of great practical interest, but of limited importance for physical knowledge of nature. However, when Coulomb, following the discovery of his celebrated law of the attraction and repulsion of electric charges, arrived at the analogous law for the poles of long, slender magnets, likewise of a purely Newtonian type, m. came to be conceived as consisting of magnetic masses acting at a distance upon one another like electric charges and material masses; m. was then regarded, like matter and electricity, as one of the fundamental constituents of the universe, in accordance with the mechanistic outlook then prevailing.
But precisely through new magnetic discoveries, after little more than two decades, the mechanistic outlook of physics was to receive its first serious refutation through Oestel’s discovery of the action of an electric current upon magnetic poles—an action whose direction stands in clear contradiction to that outlook. The subsequent construction of electromagnets, including ones consisting simply of a conductor wound helically and traversed by an electric current, clearly showed that in order to obtain the known magnetic effects it was by no means necessary to resort to hypothetical permanent magnetic masses: moving electricity was sufficient. Thus, through the initiative of Ampère, the m. of permanent natural and artificial magnets themselves came to be interpreted as the result of innumerable microscopic electromagnets, each consisting of microscopic electric currents or, in more modern terminology, of innumerable electrons rotating within the material of the magnet. Thus, ultimately, the study of m. was completely absorbed into electrology.