MAGNETISM. – From remote antiquity it was observed that certain iron minerals have the singular property that, when pieces of them are brought near one another, depending on their relative orientation, they can attract or repel each other. The Greeks called these pieces “magnets” and their property “magnetism.” In less remote times it was also observed that magnets always attract any object of iron, and that pieces of iron, or better still of hardened steel, when rubbed against them, likewise acquire that property to a greater or lesser degree. Hence the former were called “natural magnets” and the latter “artificial magnets.”
The observation that magnets, when suitably suspended, tend to orient themselves in a particular direction led to the construction of the compass, employing artificial magnets in the form of needles, 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 widely diffused only in the 13th century. In the immediately following centuries the compass was used rather empirically and its operation was incorrectly interpreted. C. Columbus, who as early as 1492, near the Island of El Hierro, had observed that the compass needle deviated from the meridian by several degrees to the west, whereas in Europe it deviated to the east, and thus had discovered the variation of magnetic declination from place to place, still shared with the scientists of his time the belief that the behavior of the magnetic needle was determined by an attractive center in the heavens.
Only G. Gilbert (1540–1603), after a notable series of observations, arrived at the correct conclusion that the earth in magnetic phenomena acts as a gigantic magnet, and he constructed a model of it, his terrella, a large spherical magnet by means of which he was able experimentally to interpret the known fact that the inclination of magnetic needles vanishes at the equator and is maximal near the magnetic poles, which he however supposed to coincide with the geographic poles; this prevented him from giving an exact interpretation of declination. His results were published in 1600.
From then until the end of the following century, further studies were devoted to terrestrial magnetism, to the localization of its poles, and to the technique of instruments; matters no doubt of great practical interest, but of limited interest for the physical understanding of nature. However, when Coulomb, after his discovery of the well-known law of attraction and repulsion of electric charges, arrived at the analogous law for the poles of long filamentary magnets, and since it was of the same strictly Newtonian type, magnetism was conceived as consisting of magnetic masses acting at a distance upon one another, just as electric charges and material masses do; magnetism was then regarded, like matter and electricity, as one of the fundamental constituents of the universe, according to the mechanistic criterion then prevailing.
But precisely through new magnetic discoveries, after little more than two decades, the mechanistic criterion of physics was to receive its first serious refutation by Ørsted’s discovery of the action of an electric current on magnetic poles; an action which, on account of its direction, stands in clear contrast to that criterion. The subsequent construction of electromagnets, even those consisting of a simple helical conductor carrying 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 moving electricity sufficed. Thus, under the initiative of Ampère, the very magnetism of natural and artificial permanent magnets 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. In this way, in the final analysis, the study of magnetism was entirely absorbed into electrology.