[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 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]