The Natural Philosophy of William Gilbert and His Predecessors Part 4

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 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 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!

The a.n.a.logy 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 a.s.sumption that under the proper conditions bodies tend to move together in order to partic.i.p.ate in a more complete unity.[119] 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[120] 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:[121] 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 partic.i.p.ation 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:[122]

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 partic.i.p.ationem unaquaeque res una dicitur. Quoniam enim nullo actio a materia potest nisi per contactum, electrica haec non videntur tangere, sed ut necesse erat demitt.i.tur 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. Aer (commune effluvium telluris) & partes disjunctis unit, & tellus mediante aere ad se revocat corpora; aliter quae in superioribus locis essent corpora, terram non ita avide appelerent.

Electrica effluvia ab aere multum differunt, & u aer 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.

[119] M: pp. 91, 92: "This unity is, according to Pythagoras, the principle, through partic.i.p.ation, in which a thing is said to be one" (see footnotes 30 and 122).

[120] "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.

[121] M: pp. 112, 113.

[122] 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:[123]

(1) coitio (vulgo attractio, dicta) ad unitatem magneticam incitatio.

(2) directio in polos telluris, et telluris in mundi destinatos terminos verticitas et consistentia.

(3) variatio, a meridiano deflexio, quem motum nos depravatum dicimus.

(4) declinatio, infra horizontem poli magnetici descensus.

(5) motus circularis, seu revolutio.

Of the five he initially listed, three are not basic ones. Variation and declination he later explained as due to irregularities of the surface of the earth, while direction or verticity is the ordering motion that precedes coition.[124] This leaves only coition and revolution as the basic motions. How these followed from "the congregant nature of the loadstone can be seen when the effusion of forms has been considered."

Coition (he did not take up revolution at this point) differed from that due to other attractions. There are two and only two kinds of bodies that can attract: electric and magnetic.[125] Gilbert refined his position further by arguing that one does not even have magnetic attraction[126] but instead the mutual motion to union that he called coition.[127] In electric attraction, one has an action-pa.s.sion relation of cause and effect with an external agent and a pa.s.sive recipient; while in magnetic coition, both bodies act and are acted upon, and both move together.[128] Instead of an agent and a patient in coition,[129] one has "conactus." Coition, as the Latin origin of the term denoted, is always a concerted action. [130] This can be seen from the motions of two loadstones floating on water.[131] The mutual motion in coition was one of the reasons for Gilbert's rejection of the perpetual motion machine of Peregrinus.[132]

[123] _Ibid._, ch. 1, pp. 45-46.

[124] M: pp. 110, 314.

[125] M: pp. 82, 105, 170, 172, 217.

[126] M: p. 98.

[127] M: pp. 100, 112, 113, 143, 148. It need hardly be pointed out that coitus is not an impersonal term.

[128] M: p. 110.