Plutarch's Platonic questions (7.7)

And neither amber nor the loadstone draws any thing to it which is near, nor does any thing spontaneously approach them. But this stone emits strong exhalations, by which the adjoining air being impelled forceth that which is before it; and this being carried round in the circle, and returning into the vacuated place, forcibly draws the iron in the same direction. In amber there is a flammeous and

spirituous nature, and this by rubbing on the surface is emitted by recluse passages, and does the same that the loadstone does. It also draws the lightest and driest of adjacent bodies, by reason of their tenuity and weakness; for it is not so strong nor so endued with weight and strength as to force much air and to act with violence and to have power over great bodies, as the magnet has. But what is the reason the air never draws a stone, nor wood, but iron only, to the loadstone? This is a common question both by them who think the coition of these bodies is made by the attraction of the loadstone, and by such as think it done by the incitement of the iron. Iron is neither so rare as wood, nor altogether so solid as gold or a stone; but has certain pores and asperities, which in regard of the inequality are proportionable to the air; and the air being received in certain seats, and having (as it were) certain stays to cling to, does not slip away; but when it is carried up to the stone and strikes against it, it draws the iron by force along with it to the stone. Such then may be the reason of this.