place it had vacated,
drags the iron forcibly along with it. The following explanation of the
virtues of the loadstone and of amber is propounded by Johannes Costaeus of
Lodi[150]. For he would have it that "there is mutual work and mutual
result, and therefore the motion is partly due to the attraction of the
loadstone and partly to a spontaneous movement on the part of the iron: For
as we say that vapours issuing from the loadstone hasten by their own
nature to attract the iron, so also the air repelled by the vapours, whilst
seeking a place for itself, is turned back, and when turned back, it impels
the iron, lifts it up, as it were, and carries it along; the iron being of
itself also excited somehow. So by being drawn out and by a spontaneous
motion, and by striking against another substance, there is in some way
produced a composite motion, which motion would nevertheless be rightly
referred to attraction, because the terminus from which this motion
invariably begins is the same terminus at which it ends, which is the
characteristic proper of an attraction." There is certainly a mutual
action, not an operation, nor does the loadstone attract in that way; nor
is there any impulsion. But neither is there that origination of the motion
by the vapours, and the turning of them back, which opinion of Epicurus has
so often been quoted by others. Galen errs in his _De Naturalibus
Facultatibus_, Book I., chap. 14, when he expresses the view that whatever
agents draw out either the venom of serpents or darts also exhibit the same
power as the loadstone. Now of what sort may be the attraction of such
medicaments (if indeed it may be called attraction) we shall consider
elsewhere. Drugs against poisons or darts have no relation to, no
similitude with, the action of magnetical bodies. The followers of Galen
(who hold that purgative medicaments attract because of similitude of
substance) say that bodies are attracted on account of similitude, not
identity, of substance; wherefore the loadstone draws iron, but iron does
not draw iron. But we declare and prove that this happens in primary
bodies, and in those bodies that are pretty closely related to them and
especially like in kind one to another, on account of their identity;
wherefore also loadstone draws loadstone and likewise iron iron; every
really true earth draws earth; and iron fortified by a loadstone within the
orbe of whose virtue it is placed draws iron more strongly tha