The Natural Philosophy of William Gilbert and His Predecessors Part 7

[204] M: p. 312.

[205] Francis Bacon, _op. cit._ (footnote 42), vol. 1, _Novum organum_, bk. 1, ch. 95, p. 306.

[206] _Ibid._, ch. 54 and ch. 64 (pp. 259 and 267).

Few of the subsequent experimenters and writers on magnetism turned to Gilbert's work to explain the effects they discussed. Although both his countrymen Sir Thomas Browne[207] and Robert Boyle[208] described a number of the experiments already described by Gilbert and even used phrases similar to his in describing them, they tended to ignore Gilbert and his explanation of them. Instead, both turned to an explanation based upon magnetic effluvia or corpuscles. The only direct continuation of Gilbert's _De magnete_ was the _Philosophia magnetica_ of Nicolaus Cabeus.[209] The latter sought to bring Gilbert's explanation of magnetism more directly into the fold of medieval substantial forms.

[207] Sir Thomas Browne, _Pseudodoxia epidemica_, ed. 3, London, 1658, bk. 2, ch. 2, 3, 4.

[208] Robert Boyle, _Experiments and notes about the mechanical production of magnetism_, London, 1676.

[209] Nicolaus Cabeaus, _Philosophia magnetica_, Ferarra, 1629.

However, Gilbert's efforts towards a magnetic philosophy did find approval in two of the men that made the seventeenth century scientific revolution. While Galileo Galilei[210] was critical of Gilbert's arguments as being unnecessarily loose, he nevertheless saw in them some support for the Copernican world-system. Johannes Kepler[211] found in Gilbert's explanation of the loadstone-earth a possible physical framework for his own investigations on planetary motions.

[210] Galileo Galilei, _Dialogue on the great world systems_, in the translation of T. Salusbury, edited and corrected by G. de Santillana, University of Chicago Press, 1953, pp.

409-423.

[211] Ca.s.sirer, _op. cit._ (footnote 3), vol. 1, p. 359-367.

Yet Galileo and Kepler had moved beyond Gilbert's world of intellectual experience. They were no longer concerned with determining the nature of material things in order to explain their qualities. Instead, they had pa.s.sed into the realm of the mathematical relations of kinematics: quant.i.tative law had replaced qualitative experience of cause and effect. Gilbert had some intimations of the former, but he was primarily concerned with explaining magnetism in terms of substance and attribute. He had to ascertain the nature of the loadstone and of the earth in order to explain their properties and their motions. He even went further and explained the nature of the form of the loadstone.

His method of determining the nature of a substance was a rather primitive one--it was not by a process of induction and deduction, nor by synthesis and a.n.a.lysis, nor by "resolutio" and "compositio," but by the use of a.n.a.logies. He compared the natural history of metals and rocks with that of plants, and gave the two former the same kind of principle as the last. He determined the nature of the ent.i.ty behind electric attraction by finding that such attractions could be screened, and hence it had to be corporeal. After comparing this "corporeal" attraction with that of the surface forces of a fluid, he concluded that the ent.i.ty was a subtle fluid. He determined the nature of the ent.i.ty behind magnetic coition by (incorrectly) finding that it cannot be screened, and hence the cause had to be a formal one. Since both stars and the loadstone can carry out regular motions, and stars had souls, the form of the loadstone had to be a soul. The method of a.n.a.logy was used again in his comparison of the properties of a magnetized needle placed over a terrella with the properties of a compa.s.s placed over the earth, whence he concluded the earth to be a giant loadstone. Since the earth resembled the other celestial globes, it had to have, the circular inertia of these globes.[212] As for his magnetic experiments to show physically that the earth moved, and his unbridled speculations on the "animae" of the celestial globes, one is inclined to agree with Bacon's estimate of his magnetic philosophy.

One might consider Gilbert's book as a Renaissance recasting of Aristotle's _De caelo_ with the earth in the role of a heavenly body.

So it might well be, for Gilbert was still concerned with distinguishing the nature of the heavenly body, earth, that caused the coitional and revolving motions, from those natures for which up and down, and coacervation were the natural motions. Because the natural motions were different, the natures had to be different, and these different natures led to a universe and a concept of s.p.a.ce neither of which were Aristotelian. One no longer had a central reference point for absolute s.p.a.ce; there was no "motor essentialis" focused upon the earth but one had only the mutual motion of the heavenly bodies. The natural distinction between heaven and earth was gone, for the earth was no longer an inert recipient but a source of wonder, and so the stage was set for the universe of Giordano Bruno.[213] The Aristotelian philosophy of nature was used to justify a new cosmology, but there was no break with the past such as one finds in Galileo and Kepler. Instead he followed the chimera of the world organism, as Paracelsus had, and of the world soul, as Bruno had. Consequently Gilbert's physiology did not enter into the main stream of science.

[212] Because the earth has the same nature as a celestial globe, its revolution and circular inertia require no more explanation than those of any other heavenly body.

[213] One wonders if Bruno might not have been another of the stimuli for Gilbert. The latter's interest in magnetism began shortly before Bruno visited England and lectured on his interpretation of the Copernican theory.

Yet this is not to deny Gilbert's services to natural philosophy.

Although not all of his experimental distinction between electric and magnetic forces has been retained, still, some of it has. His "orbis virtutis" was to become a field of force, and his cla.s.s of electrics, insulators of electricity. His practice of arming a loadstone was to be of considerable importance in the period before the invention of the electromagnet. His limited recognition of the mutual nature of forces and their quant.i.tative basis in ma.s.s was ultimately to appear in Newton's second and third laws of motion. In spite of the weaknesses of the method of a.n.a.logy, Gilbert's experimental model of the terrella to interpret the earth's magnetism was as much a contribution to scientific method as to the theory of magnetism.

Consequently, in spite of an explanation of electricity and magnetism that one would be amused to find in a textbook today, we can still read his _De magnete_ with interest and profit. But more important than his scientific speculations, is the insight he can give us into a Renaissance philosophy of nature and its relation to medieval thought.

One does not find in _De magnete_ a prototype of modern physical science in the same sense one can in the writings of Galileo and Kepler. Instead one finds here a full-fledged example of an earlier kind of science, and this is Gilbert's main value to the historian today.