g is full of gods").

[12] Plato, _Ion_, translated by W. R. M. Lamb, Loeb
Classical Library, London, 1925, 533 (see also 536).

That a mechanical explanation is also possible was shown by Plato
in his _Timaeus_.[13] He argued that since a vacuum does not exist,
there must be a plenum throughout all space. Motion of this plenum
can carry objects along with it, and one could in this manner explain
attractions like that due to amber and the loadstone.

[13] Plato, _Timaeus_, translated by R. G. Bury, Loeb
Classical Library, London, 1929, 80. It is difficult to
determine which explanation Plato preferred, for in both
cases the speaker may be only a foil for Plato's opinion
rather than an expression of these opinions.

Another mechanical explanation was based upon a postulated tendency
of atoms to move into a vacuum rather than upon the latter's
non-existence. Lucretius restated this Epicurean explanation in his
_De rerum natura_.[14] Atoms from the loadstone push away the air and
tend to cause a vacuum to form outside the loadstone. The structure of
iron is such that it, unlike other materials, can be pushed into this
empty space by the thronging atoms of air beyond it.

[14] Lucretius, _De rerum natura_, translated by W. H. D.
Rouse, Loeb Classical Library, London, 1924, bk. VI, lines
998-1041.

Galen[15] returned to a quasi-animistic solution in his denial of
Epicurus' argument, which he stated somewhat differently from
Lucretius. One can infer that Galen held that all things have, to a
greater or lesser degree, a sympathetic faculty of attracting its
specific, or proper, quality to itself.[16] The loadstone is only an
inanimate example of what one finds in nutritive organs in organic
beings.

[15] Galen, _On the natural faculties_, translated by A. S.
Brock, Loeb Classical Library, London, 1916, bk. 1 and bk. 3.
A view similar to this appeared in Plato, _Timaeus_, 81 (see
footnote 13).

[16] This same concept was to reappear in the Middle Ages as
the _inclinatio ad simile_.

One of the few writers whose explanations of the loadstone Gilbert
mentioned with approval is St. Thomas Aquinas. Although the medieval
scholastic philosophy of St. Thomas seems foreign to our way of
thinking, it formed a background to many of Gilbert's concepts, as
well as to those of his predecessors, and it will assist our
discussion to consider briefly Thomist philosoph