Part 8

M: p. 84.

M: p. 90. See also p. 95.

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

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, as Aristotle and Aquinas had argued. Accordingly, he declared, the effluvia, or "spiritus," 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."

M: p. 92.

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

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.

M: p. 94.

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. A wet body touching another wet body not only attracts it, but moves it if the other body is small, 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." 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." Moreover, a dry body does not move to the dry rim of the vessel while a wet one runs to a wet rim.

M: p. 93.

M: pp. 92, 93.

M: p. 93.

M: p. 94.

M: p. 94.

By means of the properties of such a fluid, Gilbert could explain the unordered coming-together that he called coacervation. 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.

M: p. 97.

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!

The analogy between electric attraction and fluids is a most concrete one, yet lying beneath this image is a hypothesis that is difficult to fix into a mechanical system based upon contact forces. This is the assumption that under the proper conditions bodies tend to move together in order to participate in a more complete unity. The steps in electrical attraction were described as occurring on two different levels of abstraction: first one has physical contact through an effluvium or "spiritus" that connects the two objects physically. Then, as a result of this contact, the objects somehow sense that a more intimate harmony is possible, and move accordingly. Gilbert called the motion that followed contact, attraction. However, this motion did not connote what we would call a force: it did not correspond directly to a push or pull, but it followed from what one might term the apprehension of the possibility of a more complete participation in a formal unity. The physical unity due to the "spiritus" was the prelude to a formal organic unity, so that humor is "rerum omnium unitore." Gilbert's position can be best seen in the following:

Spiritus igitur egrediens ex corpora, quod ab humore aut succo aqueo concreverat, corpus attrahendum attingit, attactum attrahenti unitur; corpus peculiari effluviorum radio continguum, unum effecit ex duobus: unita confluunt in conjunctissimam convenientiam, quae attractio vulgo dicitur. Quae unitas iuxta Pythagorae opinionem rerum omnium principium est, per cuius participationem unaquaeque res una dicitur. Quoniam enim nullo actio a materia potest nisi per contactum, electrica haec non videntur tangere, sed ut necesse erat demittitur aliquid ab uno ad aliud, quod proxime tangat, et eius incitationis principium sit. Corpora omnia uniuntur & quasi ferruminantur quodammodo humore ... Electrica vero effi via peculiaria, quae humoris fusi subtilissima sunt materia, corpuscula allectant. Aër (commune effluvium telluris) & partes disjunctis unit, & tellus mediante aëre ad se revocat corpora; aliter quae in superioribus locis essent corpora, terram non ita avide appelerent.

Electrica effluvia ab aëre multum differunt, & u aër telluris effluvium est, ita electrica suahabent effluvia & propria; peculiaribus effluviis suus cuique; est singularis ad unitatem ductus, motus ad principium, fontem, & corpus effluvia emittens.

A similar hypothesis will reappear in his explanation of magnetic attraction.

M: pp. 91, 92: "This unity is, according to Pythagoras, the principle, through participation, in which a thing is said to be one" (see footnotes 30 and 122).

"Sense" is probably too strong a term, and yet the change following contact is difficult to describe in Gilbert's phraseology without some such subjective term. See Gilbert's argument on the soul and organs of a loadstone, M: pp. 309-313.

M: pp. 112, 113.

Gilbert, De magnete, London, 1600, bk. 2, ch. 2, pp. 56-57.

Following the tradition of the medieval schoolmen Gilbert started his examination of the nature of the loadstone by pointing out the different kinds of motion due to a magnet. The five kinds (other than up and down) are: