Agreeably with the view now generally received, that magnetism and electricity are but modifications of one force, since they are found to stand to each other in the relation of cause and effect, the separation which is here adopted, of the consideration of their several phenomena, may appear inappropriate. The importance, however, of all that is connected with magnetism, and the very decided difference which is presented by true magnetic action, and that of frictional or chemical electricity, is so great that it has been thought advantageous to adopt the present arrangement in reviewing the influence of terrestrial magnetism with which science has made us acquainted. From a very early period a peculiar attractive force has been observed in some specimens of iron ore. Masses of this kind were found in Magnesia, and from that locality we derive the name given to iron in its polar condition. This is confirmed by the following lines by Lucretius:-- Quod superest agere incipiam, quo fœdere fiat Natura lapis hic ut ferrum ducere possit, 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.