The Sleepwalkers: A History of Man's Changing Vision of the Universe

by Arthur Koestler

The confusion was further increased by William Gilbert’s sensational theory that the earth was a giant loadstone, which induced Kepler to identify the sun’s action on the planets as a ‘magnetic’ force. It was quite natural, and indeed logical, that this confusion between magnetism and gravity should arise, for the loadstone was the only concrete and tangible demonstration of the mysterious tendency of matter to join matter under the influence of a ‘force’ which acted at a distance without contact or intermediaries. Hence the magnet became the archetype of action-at-a-distance and paved the way for universal gravity. Without Dr Gilbert, man would have been much less prepared to exchange the homely and traditional view that ‘weight’ meant the natural tendency of bodies to fall towards the centre for the adventurous notion that it meant the grappling of bodies at each other across empty space. Magnetism demonstrated that this grappling by ghostly fingers was a fact, that iron filings rushed to a magnet as by secret command, as stones rushed to the earth; and for about half a century the two phenomena were either identified, or regarded as Siamese twins.