d of the earth than any other metal"; it
is the hardest because of "the strong concretion of the more
earthy substance."

[54] M: pp. 21, 35, 37, 38.

[55] M: pp. 35, 63.

[56] M: pp. 45, 46.

Gilbert was indeed writing a new physiology, both in the ancient
sense of the word and the modern. The process of the formation of
metals had many biological overtones, for it was a kind of metallic
epigenesis.[57] "Within the globe are hidden the principles of metals
and stones, as at the earth's surface are hidden the principles of
herbs and plants."[58] In all cases, the "spiritus" acts as semen and
blood that inform and feed the proper womb in the generation of
animals.[59] "The brother uterine of iron,"[60] the loadstone, is
formed in this manner. As the embryo of a certain species is the
result of the specificating nature of the womb in which the generic
seed has been placed, so the kind of metal is the result of a certain
humor condensing in a particular vein in the body of the earth.

[57] Gilbert's terminology strongly suggests that he was
familiar with alchemical literature, as well as that of
medical chemistry. He has been credited as being highly
skilled in chemistry. See Sir Walter Langdon-Brown, "William
Gilbert: his place in the medical world," _Nature_, vol. 154,
pp. 136-139, 1944.

[58] _Ibid._, p. 37.

[59] M: pp. 35, 36, 53, 59. See also Galen, _op. cit._
(footnote 15) bk. 2, ch. 3.

[60] M: pp. 16, 59.

Gilbert developed this biological analogy further by ascribing to
metals a process of decay after reaching maturity. Once these solid
materials have been formed, they will degenerate unless protected,
forming earths of various kinds as a result.[61] The "rind of the
earth"[62] is produced by this process of growth and decay. If these
earths are soaked with humors, transparent materials are formed.[63]

[61] M: pp. 20, 21, 32, 61, 63, 66, 70.

[62] M: p. 59.

[63] M: p. 84.

As we shall see below, the ultimate cause of this internal and
superficial life is the motion of the earth, which animation is the
expression of the magnetic soul of this sphere.[64] As the life of
animals results from the constant working of the heart and
arteries,[65] so the daily motion of the earth results in a constant
generation of mineral life within the earth. In contrast to
Aristotle's[66] making the motion of the heavens the cause of
continuo