the surface forces ol a fluid, he concluded that the 

 entity was a subtle fluid. He determined the nature 

 of the entity behind may;netie coition by (incorrectly) 

 findina; 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 analogy was used again in 

 his comparison of the properties of a magnetized 

 needle placed over a terrella with the properties of 

 a compass 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."'" .Xs for his 

 magnetic experiments to show ])hysically tlial 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 ])hi- 

 lasophy. 



One might consider Gilbert's book as a Renais- 

 sance recasting of Aristotle's De ctiflo with liie eanh 

 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. Becau.se the natural 

 motions were different, the natures had to be difterent, 

 and these different natures led to a universe and a 

 concept of space neither of which were Aristotelian. 

 One no longer had a central reference point for 

 absolute space; there was no "motor essentialis" 

 focused upon the earth but one had oifly the mutual 

 motion of the heavenly bodies. The natural distinc- 

 tion between heaven and earth was gone, for the 

 earth was no longer an inert recipient init a source 

 of wonder, and .so the stage was set for the universe 



of Giordano Bruno. ^" The Aristotelian philcsophy 

 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. 



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 

 virtulis'' was to become a field of force, and his class 

 of electrics, insulators of electricity. His practice 

 of arming a loadstone was to be of considerable im- 

 portance in the period before the invention of the 

 electromagnet. His limited recognition of the mutual 

 nature of forces and their quantitative basis in mass 

 was ultimately to appear in Newton's .second and 

 third laws of motion. In spite of the weaknesses of 

 the intthod of analogy, 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. 



C'.onsequently, in spite cf an explanation of elec- 

 tricity 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 cf modern physical science 

 in the same sense one can in the writing.^ of Galileo 

 and Kepler. Instead one finds here a full-fledged 

 example of an earlier kind of science, and this b 

 Gilbert's main value to the historian today. 



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. 



-" One wonders if Bruno might not have lieen another of the 

 stimuli for Gilbert. The latler's interest in magnetism bcgfm 

 shortly before Bruno visited England and lectured on his 

 interpretation of the Copernican theory 



PAPER 8: NATURAL PHILOSOPHY OI- WILLIAM GILBERT 



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