us change, Gilbert made that of the earth the remote
cause.[67] However, unlike the constant cyclical transmutation of
substances in Aristotle, there is only generation and decay.

[64] M: pp. 310, 311, 312.

[65] M: p. 338. A somewhat different opinion, although not
necessarily inconsistent is expressed on p. 66, where he says
the surface is due to the action of the atmosphere, the
waters, and the radiations and other influences of heavenly
bodies.

[66] Aristotle, _op. cit._ (footnote 45), _De generatione et
corruptione_, bk. 2, ch. 10.

[67] M: pp. 311, 334, 338.

Gilbert made a number of successive generalizations in order to arrive
at the induction that the form of the loadstone is a microcosmic
"anima" of that of the earth.[68] After comparing the properties of
the loadstone and of iron, his first step in this induction was that
the two materials, found everywhere,[69] are consanguineous:[70]
"These two associated bodies possess the true, strict form of one
species, though because of the outwardly different aspect and the
inequality of the selfsame innate potency, they have hitherto been
held to be different ..." Good iron and good loadstone are more
similar than a good and a poor loadstone, or a good and a poor iron
ore.[71] Moreover, they have the same potency,[72] for the innate
potency of one can be passed to the other:[73] "The stronger
invigorates the weaker, not as if it imparted of its own substances or
parted with aught of its own strength, nor as if it injected into the
other any physical substance; but rather the dormant power of the one
is awakened by the other's without expenditure." In addition, the
potency can be passed only to the other.[74] Finally they both have
the same history:

We see both the finest magnet and iron ore visited as it were
by the same ills and diseases, acting in the same way and
with the same indications, preserved by the same remedies and
protective measures, and so retaining their properties ...
they are both impaired by the action of acrid liquids as
though by poison[75] ... each is saved from impairment by
being kept in the scrapings of the other. [So] ... form,
essence and appearance are one.[76]

Any difference between the loadstone proper and the iron proper is due
to a difference in the actual power of the magnetic virtue:[77] "Weak
loadstones are those disfigured with dross metallic humors a