Part 4 (1/2)

The source of the effluvia could be inferred from the properties of the electrics. Many but not all of the electrics are transparent, but all are firm and can be polished.[98] Since they retain the appearance and properties of a fluid in a firm solid ma.s.s,[99] Gilbert concluded 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 const.i.tuted 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 s.h.i.+ny 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 Cla.s.sical 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 primum movens immobile), cap. d, p. 96.

[110] M: p. 94.

[111] M: p. 95.

It can be seen how this uniting action is effected if objects floating on water are considered, for solids can be drawn to solids through the medium of a fluid.[112] A wet body touching another wet body not only attracts it, but moves it if the other body is small,[113] while wet bodies on the surface of the water attract other wet bodies. A wet object on the surface of the water seeks union with another wet object when the surface of the water rises between both: at once, ”like drops of water, or bubbles on water, they come together.”[114] On the other hand, ”a dry body does not move toward a wet, nor a wet to a dry, but rather they seem to go away from one another.”[115] Moreover, a dry body does not move to the dry rim of the vessel while a wet one runs to a wet rim.[116]

[112] M: p. 93.

[113] M: pp. 92, 93.

[114] M: p. 93.

[115] M: p. 94.

[116] M: p. 94.

By means of the properties of such a fluid, Gilbert could explain the unordered coming-together that he called coacervation.[117] Different bodies have different effluvia, and so one has coacervation of different materials. Thus, in Gilbert's philosophy air was the earth's effluvium and was responsible for the unordered motion of objects towards the earth.[118]

[117] M: p. 97.

[118] M: p. 92 (see also p. 339). Although Gilbert does not make it explicit, this would solve the medieval problem of gravitation without resorting to a Ptolemaic universe. In addition, since coacervation is electric, and electric forces can be screened, it should have been possible to reduce the downward motion of a body by screening!