longer concerned with
determining the nature of material things in order to explain their
qualities. Instead, they had passed into the realm of the mathematical
relations of kinematics: quantitative law had replaced qualitative
experience of cause and effect. Gilbert had some intimations of the
former, but he was primarily concerned with explaining magnetism in
terms of substance and attribute. He had to ascertain the nature of
the loadstone and of the earth in order to explain their properties
and their motions. He even went further and explained the nature of
the form of the loadstone.

His method of determining the nature of a substance was a rather
primitive one--it was not by a process of induction and deduction, nor
by synthesis and analysis, nor by "resolutio" and "compositio," but by
the use of analogies. He compared the natural history of metals and
rocks with that of plants, and gave the two former the same kind of
principle as the last. He determined the nature of the entity behind
electric attraction by finding that such attractions could be
screened, and hence it had to be corporeal. After comparing this
"corporeal" attraction with that of the surface forces of a fluid, he
concluded that the entity was a subtle fluid. He determined the nature
of the entity behind magnetic coition by (incorrectly) finding that it
cannot be screened, and hence the cause had to be a formal one. Since
both stars and the loadstone can carry out regular motions, and stars
had souls, the form of the loadstone had to be a soul. The method of
analogy was used again in his comparison of the properties of a
magnetized needle placed over a terrella with the properties of a
compass placed over the earth, whence he concluded the earth to be a
giant loadstone. Since the earth resembled the other celestial globes,
it had to have, the circular inertia of these globes.[212] As for his
magnetic experiments to show physically that the earth moved, and his
unbridled speculations on the "animae" of the celestial globes, one is
inclined to agree with Bacon's estimate of his magnetic philosophy.

One might consider Gilbert's book as a Renaissance recasting of
Aristotle's _De caelo_ with the earth in the role of a heavenly body.
So it might well be, for Gilbert was still concerned with
distinguishing the nature of the heavenly body, earth, that caused the
coitional and revolving motions, from those natures for which up and
down, and coacervation