121, where the lodestone is defined as "a stone with which an attraction can be given to a needle," but this knowledge is no more than that existing in Europe at least five hundred years before.
Roger Bacon (Opus majus and Opus minus, 1266-1267) was acquainted with the properties of the lodestone, and wrote that if set so that it can turn freely (swimming on water) it points toward the poles; but he stated that this was not due to the pole-star, but to the influence of the northern region of the heavens.
No sea-going ships were built in China before 139 B.C. The earliest allusion to the power of the lodestone in Chinese literature occurs in a Chinese dictionary, finished in A.D.
Many of their compounds are very strongly magnetic, erbium, for example, in Er203 being four times as strong as iron in the familiar magnetite or lodestone, Fe203.
And Chronological Notes The most conspicuous property of the lodestone, its attraction for iron, appears to have been familiar to the Greeks at least as early as 800 B.C., and is mentioned by Homer, Plato, Aristotle, Theophrastus and others.