Quem magnêta vocant patrio de nomine Graii
Magnêtum, quia sit patriis in finibus ortus.
Again we find Pliny employing the term magnetic, to express this singular power. It was known to the ancients that the magnetic power of iron, and the electric property of amber, were not of the same character, but they were both alike regarded as miraculous. The Chinese and Arabians seem to have known Magnetism at a period long before that at which Europeans became acquainted with either the natural loadstone or the artificial magnet. Previously to a.d. 121, the magnet is distinctly mentioned in a Chinese dictionary; and in a.d. 419 it is stated in another of their books that ships were steered south by it.[170]
The earliest popularly received account of its use in Europe is, that Vasco de Gama employed a compass in 1427, when that really adventurous navigator first explored the Indian seas. It is highly probable, however, that the knowledge of its important use was derived from some of the Oriental nations at a much earlier period.
We have some curious descriptions of the leading stone or loadstone, in the works of an Icelandic historian, who wrote in 1068. The mariner’s compass is described in a French poem of the date of 1181; and from Torfæus’s History of Norway, it appears to have been known to the northern nations certainly in 1266.
We have not to deal with the history of magnetic discovery, but so far as it tells of the strange properties which magnets are found to possess, and the application of this knowledge to the elucidation of effects occurring in nature.
A brown stone, in no respect presenting anything by which it shall be distinguished from other rude stones around it, is found, upon close examination, to possess the power of drawing light particles of iron towards it. If this stone is placed upon a table, and iron filings are thrown lightly around it, we discover that these filings arrange themselves in symmetric curves, proceeding from some one point of the mass to some other; and upon examining into this, we shall find that the iron which has once clung to the one point will be rejected by the other. If this stone is freely suspended, we shall learn also that it always comes to rest in a certain position,—this position being determined by these points, and some attractive force residing in the earth itself. These points we call its poles; and it is now established that this rude stone is but a small representative of our planet. Both are magnetic: both are so in virtue of the circulation of currents of electricity, or of lines of magnetic force, as seen in the curves formed by the iron dust, and the north pole of the one attracts the south pole of the other, and the contrary. By a confusion of terms we speak of the north pole of a compass-needle, meaning that point which is always opposite to the north pole of the earth: the truth being that the pole of the compass-needle, which is so forcibly drawn to the north, is a point in a contrary state, or, as we may express it, really a south pole.
There is a power of a peculiar kind, differing from gravitation, or any other attracting or aggregating force with which we are acquainted, which exists permanently in the magnetic iron stones, and also in the earth. What is this power?