The Natural Philosophy of William Gilbert and His Predecessors Part 3

[61] M: pp. 20, 21, 32, 61, 63, 66, 70.

[62] M: p. 59.

[63] M: p. 84.

As we shall see below, the ultimate cause of this internal and superficial life is the motion of the earth, which animation is the expression of the magnetic soul of this sphere.[64] As the life of animals results from the constant working of the heart and arteries,[65] so the daily motion of the earth results in a constant generation of mineral life within the earth. In contrast to Aristotle's[66] making the motion of the heavens the cause of continuous change, Gilbert made that of the earth the remote cause.[67] However, unlike the constant cyclical trans.m.u.tation of substances in Aristotle, there is only generation and decay.

[64] M: pp. 310, 311, 312.

[65] M: p. 338. A somewhat different opinion, although not necessarily inconsistent is expressed on p. 66, where he says the surface is due to the action of the atmosphere, the waters, and the radiations and other influences of heavenly bodies.

[66] Aristotle, _op. cit._ (footnote 45), _De generatione et corruptione_, bk. 2, ch. 10.

[67] M: pp. 311, 334, 338.

Gilbert made a number of successive generalizations in order to arrive at the induction that the form of the loadstone is a microcosmic "anima" of that of the earth.[68] After comparing the properties of the loadstone and of iron, his first step in this induction was that the two materials, found everywhere,[69] are consanguineous:[70]

"These two a.s.sociated bodies possess the true, strict form of one species, though because of the outwardly different aspect and the inequality of the selfsame innate potency, they have hitherto been held to be different ..." Good iron and good loadstone are more similar than a good and a poor loadstone, or a good and a poor iron ore.[71] Moreover, they have the same potency,[72] for the innate potency of one can be pa.s.sed to the other:[73] "The stronger invigorates the weaker, not as if it imparted of its own substances or parted with aught of its own strength, nor as if it injected into the other any physical substance; but rather the dormant power of the one is awakened by the other's without expenditure." In addition, the potency can be pa.s.sed only to the other.[74] Finally they both have the same history:

We see both the finest magnet and iron ore visited as it were by the same ills and diseases, acting in the same way and with the same indications, preserved by the same remedies and protective measures, and so retaining their properties ...

they are both impaired by the action of acrid liquids as though by poison[75] ... each is saved from impairment by being kept in the sc.r.a.pings of the other. [So] ... form, essence and appearance are one.[76]

Any difference between the loadstone proper and the iron proper is due to a difference in the actual power of the magnetic virtue:[77] "Weak loadstones are those disfigured with dross metallic humors and with foreign earth admixtures, [hence one may conclude] they are further removed from the mother earth and are more degenerate."

[68] M: pp. xlvii, 309, 328.

[69] M: pp. 18, 20, 44, 46, 69.

[70] M: pp. 59, 61, 63.

[71] M: pp. 60, 63.

[72] M: p. 110.

[73] M: pp. 60, 61.

[74] M: p. 62.

[75] M: p. 63.

[76] M: p. 60.

[77] M: pp. 19, 21, 43, 53, 61, 63, 184.

Gilbert's second induction was that they are "true and intimate parts of the globe,"[78] that is, that they are piece of the "materia prima"

of all we see about us. For they "seem to contain within themselves the potency of the earth's core and of its inmost viscera."[79]

Whence, in Gilbert's philosophy, the earthy matter of the elements was not pa.s.sive or inert[80] as it was in Aristotle's, but already had the magnetic powers of loadstone. Being endowed with properties, it was, in peripatetic terms, a simple body.

[78] M: p. 61.

[79] M: pp. 66, 67.

[80] M: p. 69. Gilbert is confusing Aristotelian matter and an element. He includes cold and dry, with formless and inert! See also Maier, _op. cit._ (footnote 17).

If these pieces of earth proper, before decay, are loadstones, then one may pa.s.s to the next induction that the earth itself is a loadstone.[81] Conversely, a terrella has all the properties of the earth:[82] "Every separate fragment of the earth exhibits in indubitable experiments the whole impetus of magnetic matter; in its various movements it follows the terrestial globe and the common principle of motion."[83]

[81] M: p. 63; bk. 1, ch. 17.

[82] M: pp. 67, 181-183, 235-240, 281-289, 313-314.

[83] M: p. 71. See also pp. 314 and 331. It is not clear, at this point, whether he believed a "properly balanced"

terrella would be a _perpetuum mobile_.

The next induction that Gilbert made was that as the magnet possesses verticity and turns towards the poles, so the loadstone-earth possesses a verticity and turns on an axis fixed in direction.[84] He could now discuss the motions of a loadstone in general, in terms of its nature, just as an Aristotelian discussed the motion of the elements in terms of their nature.

[84] M: pp. 68, 70-71, 97, 129, 179-180, 311, 315, 317-335 Gilbert implied (M: p. 166), that a terrella does not rotate as Peregrinus said, due to resistance (M: p. 326), or due to the mutual nature of coition (M: p. 166); or even to the rotation of the earth (M: p. 332). However (M: p. 129), he also mentioned that a terrella would revolve by itself!

But before reaching this point in his argument, Gilbert digressed to cla.s.sify the different kinds of attractions and motions which the elements produce. In particular, he distinguished electric attraction from magnetic coition, and pointed out the main features of electrical attraction. Since the resultant motions were different, the essential natures of electric and magnetic substances had to differ.

Gilbert introduced his treatment of motion by discussing the attraction of amber. All sufficiently light solids[85] and even liquids,[86] but not flame or air[87] are attracted by rubbed amber.

Heat from friction,[88] but not from alien sources like the sun[89] or the flame,[90] produce this "affection." By the use of a detector modeled after the magnetic needle, which we would call an electroscope but which he called a "versorium,"[91] Gilbert was able to extend the list of substances that attract like amber.[92] These Gilbert called "electricae."[93]

[85] M: pp. 78, 82, 84, 86.

[86] M: pp. 78, 89, 91.

[87] M: pp. 89, 95.

[88] M: pp. 83, 86.

[89] M: pp. 81, 86, 87.

[90] M: pp. 80, 81, 86, 87.

[91] M: p. 79.

[92] M: pp. 77-78, 79.

[93] M: p. 78. The definition Gilbert gave of an electric in the glossary at the beginning of his treatise was not an experimental one: "Electricae, quae attrahunt eadem ratione ut electrum."

Possibly as a result of testing experimentally statements like that of St. Thomas, on the effect of garlic on a loadstone, Gilbert discovered that the interposition of even the slightest material (except a fluid like olive oil) would screen the attraction of electrics.[94] Hence the attraction is due to a material cause, and, since it is invisible, it is due to an effluvium.[95] It must be much rarer than air,[96] for if its density were that of air or greater, it would repel rather than attract.[97]

[94] M: pp. 86, 91, 135.

[95] M: pp. 96, 135.

[96] M: p. 89.

[97] M: pp. 90, 92, 95.