On the Magnet, by William Gilbert

Chap. vi.

That variation and direction arise from the disponent power of the earth, and from the natural magnetick tendency to rotation, not from attraction, or from coition, or from other occult cause.

O wing to the loadstone being supposed (amongst the crowd of philosophizers) to seize and drag, as it were, magnetick bodies; and since, in truth, sciolists have remarked no other forces than those so oft besung of attractive ones, they therefore deem every motion toward the north and south to be caused by some alluring and inviting quality. But the Englishman, Robert Norman, first strove to show that it is not caused by attraction: wherefore, as if tending toward hidden principles, he imagined a point respective224, toward which the iron touched by a loadstone would ever turn, not a point attractive; but in this he erred greatly, although he effaced the former error about attraction. He, however, demonstrates his opinion in this way:

Robert Norman's demonstration.

Let there be a round vessel filled with water: in the middle of the surface of the water place a slender iron wire on a perfectly round cork, so that it may just float in æquilibrium on the water; let the wire be previously touched by a magnet, so that it may more readily show the point of variation, the point D as it were: and let it remain on the surface for some time. It is demonstrable that the wire together with the cork is not moved to the side D of the vessel: which it would do if an attraction came to the iron wire by D: and the cork would be moved out of its place. This assertion of the Englishman, Robert Norman, is plausible and appears to do away with attraction because the iron remains on the water not moving about, as well in a direction toward the pole itself (if the direction be true) as in a variation or altered direction; and it is moved about its own centre without any transference to the edge of the vessel. But direction does not arise from attraction, but from the disposing and turning power which exists in the whole earth, not in the pole or in some other attracting part of the stone, or in any mass rising above the periphery of the true circle so that a The magnetick force exists in the whole. variation should occur because of the attraction of that mass. Moreover, it is the directing power of the loadstone and iron and its natural power of turning around the centre which cause the motion of direction, and of conformation, in which is included also the motion of the dip. And the terrestrial pole does not attract as if the terrene force were implanted only in the pole, for the magnetick force exists in the whole, although it predominates and excels at the pole. Wherefore that the cork should rest quiescent in the middle and that the iron excited by a loadstone should not be moved toward the side of the vessel are agreeable to and in conformity with the magnetick nature, as is demonstrated by a terrella: for an iron spike placed on the stone at C clings on at C, and is not pulled * further away by the pole A, or by the parts near the pole: hence it persists at D, and takes a direction toward the pole A; nevertheless it clings on at D and dips also at D in virtue of that turning power by which it conforms itself to the terrella: of which we will say more in the part On Declination.

224 Page 162, line 2. Page 162, line 3. quarè & respectiuum punctum . . . excogitauit.— The passage referred to is in The newe Attractiue of Robert Norman (Lond., 1581), chap. vi.

"Your reason towards the earth carrieth some probabilitie, but I prove that there be no Attractive, or drawing propertie in neyther of these two partes, then is the Attractive poynt lost, and falsly called the poynt Attractive, as shall be proved. But because there is a certayne point that the Needle alwayes respecteth or sheweth, being voide and without any Attractive propertie: in my judgment this poynt ought rather to bee called the point Respective . . . This Poynt Respective, is a certayne poynt, which the touched Needle doth alwayes Respect or shew . . . "

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Last updated Friday, March 14, 2014 at 22:17