On the Magnet, by William Gilbert

Chap. xxxix. On Bodies which mutually repel one another.

W riters who have discoursed on the forces of bodies which attract others have also spoken about the powers of bodies which repel, but especially those who have instituted classes for natural objects on the basis of sympathy and antipathy. Wherefore it would seem necessary for us to speak also about the mutual strife of bodies, so that published errors should not creep further, and be received by all to the ruin of true philosophy. They say that, just as like things attract for the sake of preservation, so unlike and contrary things for the same purpose mutually repel and put one another to flight. This is evident in the reaction of many things, but it is most manifest in the case of plants and animals, which attract kindred and familiar things, and in like manner reject foreign and unsuitable things. But in other bodies there is not the same reason, so that when they are separated, they should come together by mutually attracting one another. Animals take food (as everything which grows), and draw it into their interior; they absorb the nourishment by certain parts and instruments (through the action and operation of the anima). They enjoy by natural instinct only the things set in front of them and near them, not things placed afar off; and this without any alien force or motion. Wherefore animals neither attract any bodies nor drive them away. Water does not repel oil (as some think) because the oil floats on water; nor does water repel mud, because the mud, if mixed in water, settles down in time. This is a separation of unlike bodies or such as are not perfectly mixed as respects the material; the separated bodies nevertheless remain joined without any natural strife. Wherefore a muddy sediment settles quietly on the bottom of vessels, and oil remains on the top of the water and is not sent further away. A drop of water remains intact on a dry surface, and is not expelled from the dry substance. Wrongly therefore do those who discourse on these matters infer an antipathy (that is, the force of repelling by contrary passions); for there is no repelling force in them; and repulsion comes193 from action, not from passion. But their greek vocables please them too much. We, however, must inquire whether there is any body which drives anything else further off without material impetus, as a loadstone attracts. But a loadstone seems even to repel loadstone. For the pole of one loadstone repels the pole of another, which does not agree with it according to nature; by repelling, it turns it round in an orbit so that they may exactly agree according to their nature. But if a somewhat weak loadstone, floating freely on water, cannot readily be turned round on account of impediments, the whole loadstone is repelled and sent further away from the other. All electricks attract all things: they never repel or propel anything at all194. As to what is related about certain plants (as about the cucumber, which turns aside when oil is applied to it), there is a material change from the vicinity, not a hidden antipathy. But when they show a candle flame put against a cold solid substance (as iron) turn away to the side, and allege antipathy as the cause, they say nothing. The reason of this they will see clearer than the day, when we discourse on what heat is195. But Fracastorio’s opinion that a loadstone can be found, which would drive iron away, on account of some opposing principle lurking in the iron, is foolish.

193 Page 113, line 14. Page 113, line 19. repulsus sit. The words read thus in all editions, but the sense requires repulsa sint.

194 Page 113, line 23. Page 113, line 29. Electrica omnia alliciunt cuncta, nihil omninò fugant vnquam, aut propellunt. This denial of electrical repulsion probably arose from the smallness of the pieces of electric material with which Gilbert worked. He could hardly have failed to notice it had he used large pieces of amber or of sealing-wax. Electrical repulsion was first observed by Nicolas Cabeus, Philosophia Magnetica, Ferrara, 1629; but first systematically announced by Otto von Guericke in his treatise Experimenta Nova (ut vocantur) Magdeburgica, de Vacuo Spatio (Amstel., 1672).

195 Page 113, line 29. Page 113, line 37. cùm de calore quid sit disputabimus.— The discussion of the nature of heat is to be found in Gilbert’s De Mundo nostro Sublunari (Amstel., 1651), lib. i., cap. xxvi., pp. 77-88.


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