that they derived their growth mostly from humors or were concretions
of humors.[100] By friction, these humors are released and produce
electrical attraction.[101]

[98] M: pp. 83, 84, 85.

[99] M: p. 84.

[100] M: pp. 84, 89. See also Aristotle, _op. cit._ (footnote
45), _Meteorologica_, bk. 4.

[101] M: p. 90.

This humoric source of the effluvia was substantiated by Gilbert in a
number of ways. Electrics lose their power of electrical attraction
upon being heated, and this is because the humor has been driven
off.[102] Bodies that are about equally constituted of earth and
humor, or that are mostly earth, have been degraded and do not show
electrical attraction.[103] Bodies like pearls and metals, since they
are shiny and so must be made of humors, must also emit an effluvium
upon being rubbed, but it is a thick and vaporous one without any
attractive powers.[104] Damp weather and moist air can weaken or even
prevent electrical attraction, for it impedes the efflux of the humor
at the source and accordingly diminishes the attraction.[105] Charged
bodies retain their powers longer in the sun than in the shade, for in
the shade the effluvia are condensed more, and so obscure
emission.[106]

[102] M: pp. 84, 85.

[103] M: p. 84.

[104] M: p. 90. See also p. 95.

[105] M: pp. 78, 85-86, 91. (see particularly the heated
amber experiment described on p. 86).

[106] M: p. 87.

All these examples seemed to justify the hypothesis that the nature of
electrics is such that material effluvia are emitted when electrics
are rubbed, and that the effluvia are rarer than air. Gilbert realized
that as yet he had not explained electrical attraction, only that the
pull can be screened. The pull must be explained by contact
forces,[107] as Aristotle[108] and Aquinas[109] had argued.
Accordingly, he declared, the effluvia, or "spiritus,"[110] emitted
take "hold of the bodies with which they unite, enfold them, as it
were, in their arms, and bring them into union with the
electrics."[111]

[107] M: p. 92.

[108] Aristotle, _Physics_, translated by P. H. Wicksteed and
F. M. Cornford, Loeb Classical Library, London, 1934, bk. 7,
ch. 1, 242b25.

[109] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 2,
_Physicorum Aristotelis expositio_, lib. 7, lect. 2 (In
moventibus et motis non potest procedi in infinitum, sed
oportet devenire ad aliquid