Part 9

(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. 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. Gilbert refined his position further by arguing that one does not even have magnetic attraction but instead the mutual motion to union that he called coition. In electric attraction, one has an action-passion relation of cause and effect with an external agent and a passive recipient; while in magnetic coition, both bodies act and are acted upon, and both move together. Instead of an agent and a patient in coition, one has "conactus." Coition, as the Latin origin of the term denoted, is always a concerted action. This can be seen from the motions of two loadstones floating on water. The mutual motion in coition was one of the reasons for Gilbert's rejection of the perpetual motion machine of Peregrinus.

Ibid., ch. 1, pp. 45-46.

M: pp. 110, 314.

M: pp. 82, 105, 170, 172, 217.

M: p. 98.

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

M: p. 110.

M: p. 110.

M: pp. 109, 115, 148, 149, 155, 166, 174.

M: pp. 110, 155.

M: pp. 166, 332. See also footnote 84.

Magnetic coition, unlike electric attraction, cannot be screened. Hence it cannot be corporeal for it travels freely through bodies and especially magnetic bodies; one can understand the action of the armature on this basis. Since coition cannot be prevented by shielding, it must have an immaterial cause.

M: pp. 90, 106, 107, 108, 113, 132, 135, 136, 158. This is, of course, contrary to modern experience.

M: pp. 106, 107, 108, 114, 134, 136, 140, 162.

M: pp. 106, 109, 114, 159, 162.

M: pp. 137-140.

M: p. 109.

Yet, unless one has the occult action-at-a-distance, change must be caused by contact forces. Gilbert resolved the paradox of combining contact forces with forces that cannot be shielded, by passing to a higher level of abstraction for the explanation of magnetic phenomena: he saw the contact as that of a form with matter.

Although Gilbert remarked that the cause of magnetic phenomena did not fall within any of the categories of the formal causes of the Aristotelians, he did not renounce for this reason the medieval tradition. Actually there are many similarities between Gilbert's explanation of the loadstone's powers and that of St. Thomas. Magnetic coition is not due to any of the generic or specific forms of the Aristotelian elements, nor is it due to the primary qualities of any of their elements, nor is it due to the celestial "generans" of terrestrial change.

Relictis aliorum opinionibus de magnetis attractione; nunc coitionis illius rationem, et motus illius commoventem naturam docebimus. Cum vero duo sint corporum genera, quae manifestis sensibus nostris motionibus corpora allicere videntur, Electrica et Magnetica; Electrica naturalibus ab humore effluviis; Magnetica formalibus efficientiis, seu potius primariis vigoribus, incitationes faciunt. Forma ilia singularis est, et peculiaris, non Peripateticorum causa formalis, et specifica in mixtis, est secunda forma, non generantium corporum propagatrix; sed primorum et praeciporum globorum forma; et partium eorum homogenearum, non corruptarum, propria entitas et existentia, quam nos primariam, et radicalem, et astream appellare possumus formam; non formam primam Aristotelis; sed singularem illam, quae globum suum proprium tuetur et disponit. Talis in singulis globis, Sole, lunas et astris, est una; in terra etiam una, quae vera est ilia potentia magnetica, quam nos primarium vigorem appellamus. Quare magnetica natura est telluris propria, eiusque omnibus verioribus partibus, primaria et stupenda ratione, insita; haec nec a caelo toto derivatur procreaturve, per sympathiam, per influentiam, aut occultiores qualitates; nec peculiari aliquo astro: est enim suus in tellure magneticus vigor, sicut in sole et luna suae formae; frustulumque; lunae, lunatice ad eius terminos, et formam componit se; solarque; ad solem, sicut magnes ad tellurem, et ad alterum magnetem, secundum naturam sese inclinando et alliciendo. Differendum igitur de tellure quae magnetica, et magnes; tum etiam de partibus eius verioribus, quae magneticae sunt; et quomodo ex coitione difficiuntur.

Instead, he declared it to be due to a form that is natural and proper to that element that he made the primary component of the earth.

To understand his argument, let us briefly recall the peripatetic theory of the elements. In this philosophy of nature each element or simple body is a combination of a pair of the four primary qualities that informs inchoate matter. These qualities are the instruments of the elemental forms and determine the properties of the element. Thus the element fire is a compound of the qualities hot and dry, and the substantial form of fire acts through these qualities. Similarly for the other elements, earth, water, and air: their forms determine a proper place for each element, and a motion to that place natural to each element.