The Natural Philosophy of William Gilbert and His Predecessors Part 5

[129] M: p. 110.

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

[131] M: pp. 110, 155.

[132] M: pp. 166, 332. See also footnote 84.

Magnetic coition, unlike electric attraction, cannot be screened.[133]

Hence it cannot be corporeal for it travels freely through bodies[134]

and especially magnetic bodies;[135] one can understand the action of the armature on this basis.[136] Since coition cannot be prevented by shielding, it must have an immaterial cause.[137]

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

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

[135] M: pp. 106, 109, 114, 159, 162.

[136] M: pp. 137-140.

[137] 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 pa.s.sing 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.[138]

Relictis aliorum opinionibus de magnetis attractione; nunc coitionis illius rationem, et motus illius commoventem naturam docebimus. c.u.m 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 h.o.m.ogenearum, non corruptarum, propria ent.i.tas et existentia, quam nos primariam, et radicalem, et astream appellare possumus formam; non formam primam Aristotelis; sed singularem illam, quae glob.u.m 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.[139]

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.[140]

[138] M: p. 105, and Gilbert, _De magnete_, London, 1600, bk.

2 ch. 4, p. 65.

[139] M: p. 105.

[140] M: pp. 289, 322.

Gilbert had previously declared that the primary substance of the earth is an element. Since it is an element, it has a motion natural to it, and this motion is magnetic coition. As an Aristotelian considered the substantial form of the element, fire, to act through the qualities of hot and dry, and to cause an upward motion; so Gilbert argued that the substantial form of his element, pure loadstone, acts through the magnetic qualities and causes magnetic coition. This motion is due to its primary form, and is natural to the element earth.[141] It is instilled in all proper and undegenerate parts of the earth,[142] but in no other element.[143]

[141] M: pp. 26, 68, 105, 179, 198, 307, 335, 343. For rotation, see footnote 147.

[142] M: pp. 67, 71. That each part is informed with the properties of the whole is an argument favoring an animistic explanation of the nature of this form.

[143] M: p. 109.

To the medieval philosopher, the "generantia" of the occult powers of the loadstone are the heavenly bodies. Gilbert, however, endowed the earth with these heavenly powers which were placed in the earth in the beginning[144] and caused all magnetic materials to conform with it both physically and formally.[145] Such magnetic powers are the property of all parts of the earth;[146] they give the earth its rotating motion[147] and hold the earth together in spite of this motion.[148]

[144] M: pp. 111, 188.

[145] M: pp. 67, 105, 179, 183.

[146] M: pp. 101, 105, 217.

[147] M: pp. 179, 304, 305, 311, 322, 326, 328, 330-334, 338-343.

[148] M: pp. 142, 179; see also electric attraction, p. 97.

Indeed, each of the main stellar bodies, sun, moon, stars, and earth, has such a form or principle unique to itself that causes its parts not only to conform with itself but to revolve.[149] Thus, if one removes a piece of the moon from this body, it will tend to align itself with the moon and then to return to its proper place; and a fragment of the sun would similarly tend to return after proper orientation.[150] Moreover, there is a farther-ranging, though weaker, mutual action of the heavenly bodies so that one has a causal hierarchy of these specific conforming powers. The form of the sun is superior to that of the inferior globes and is responsible for the order and regularity of planetary orbits.[151] In like manner, the moon is responsible for the tides of the ocean.[152]

[149] M: pp. 308, 317-343.

[150] M: pp. 106, 340.

[151] M: pp. 308, 309, 311, 330, 333, 344, 347.

[152] M: pp. 136, 334, 345.

By virtue of the causal hierarchy of forms, the loadstone acquires its magnetic powers from the earth.[153] As the earth has its natural parts, so has the stone.[154] Although the geometrical center of a terrella is the center of the magnetic forces,[155] objects do not tend to move to the center but to its poles,[156] where the magnetic energy is most conspicuous.[157] However, in a sense, the energy is everywhere equal: the virtue is spread throughout the entire ma.s.s of the loadstone,[158] and all the parts direct the forces to the poles.[159] The poles become the "thrones" of the magnetic powers.[160] On the other hand, the directive force is stronger where coition is weaker and accordingly, verticity is most prominent at the equator.[161]

[153] M: pp. 184-186, 190, 232. This is not quite the same argument as that the powers of the loadstone are identical with those of the earth. See footnote 78.

[154] M: pp. 125, 180.

[155] M: p. 151.

[156] M: pp. 121, 150.

[157] M: pp. 115, 151, 165.

[158] M: pp. 106, 118, 151, 191, 205, 221, 243.

[159] M: pp. 116, 117, 119, 131, 183, 188, 221.

[160] M: p. 31.

[161] M: pp. 116, 151, 200.

The strength of a loadstone depends upon its shape and ma.s.s. A bar magnet has greater powers than a spherical one because it tends to concentrate the magnetic powers more in the ends.[162] For a given purity and shape, the heavier the loadstone, the greater its strength.[163] A loadstone has a maximum degree of magnetic force that cannot be increased.[164] However, weaker ones can be strengthened by stronger ones.[165] Similarly, the shape and weight of the iron determine the magnetic force in coition.[166]

[162] M: pp. 131, 132, 153-158.

[163] M: pp. 141, 152, 153, 158, 161, 191, 222.

[164] M: p. 146.

[165] M: p. 165.

[166] M: p. 153.