chap. iii.
opinions of others on magnetick coition, which they call attraction.
d iscussion having now been made concerning electricks, the causes of magnetick coition must be set forth. we say coition, not attraction146. the word attraction unfortunately crept into magnetick philosophy from the ignorance of the ancients; for there seems to be force applied where there is attraction and an imperious violence dominates. for, if ever there is talk about magnetick attraction, we understand thereby magnetick coition, or a primary running together. now in truth it will not be useless here first briefly to set forth the views given by others, both the ancient and the more modern writers. orpheus in his hymns147 narrates that iron is attracted by loadstone as the bride to the arms of her espoused. epicurus holds that iron is attracted by a loadstone just as straws by amber; "and," he adds, "the atoms and indivisible particles which are given off by the stone and by the iron fit one another in shape; so that they easily cling to one another; when therefore these solid particles of stone or of iron strike against one another, then they rebound into space, being brought against one another by the way, and they draw the iron along with them." but this cannot be the case in the least; since solid and very dense substances interposed, even squared blocks of marble, do not obstruct this power, though they can separate atoms from atoms; and the stone and the iron would be speedily dissipated into such profuse and perpetual streams of atoms. in the case of amber, since there is another different method of attracting, the epicurean atoms cannot fit one another in shape. thales, as aristotle writes, de anima, bk. i., deemed the loadstone to be endowed with a soul of some sort, because it had the power of moving and drawing iron towards it. anaxagoras also held the same view. in the timæus of plato there is an idle fancy148 about the efficacy of the stone of hercules. for he says that "all flowings of water, likewise the fallings of thunderbolts, and the things which are held wonderful in the attraction of amber, and of the herculean stone, are such that in all these there is never any attraction; but since there is no vacuum, the particles drive one another mutually around, and when they are dispersed and congregated together, they all pass, each to its proper seat, but with changed places; and it is forsooth, on account of these intercomplicated affections that the effects seem to arouse the wonder in him who has rightly investigated them." galen does not know why plato should have seen fit to select the theory of circumpulsion rather than that of attraction (differing almost on this point alone from hippocrates), though indeed it does not agree in reality with either reason or experiment. nor indeed is either the air or anything else circumpelled; and the bodies themselves which are attracted are carried towards the attracting substance not confusedly, or in an orbe. lucretius, the poet of the epicurean sect, sang his opinion of it thus:
149first, then, know,
ceaseless effluvia from the magnet flow —
effluvia, whose superior powers expel
the air that lies between the stone and steel.
a vacuum formed, the steely atoms fly
in a link'd train, and all the void supply;
while the whole ring to which the train is join'd
the influence owns, and follows close behind. &c.
such a reason plutarch also alleges in the quæstiones platonicæ: that that stone gives off heavy exhalations, whereby the adjacent air, being impelled along, condenses that which is in front of it; and that air, being driven round in an orbe and reverting to the place it had vacated, drags the iron forcibly along with it. the following explanation of the virtues of the loadstone and of amber is propounded by johannes costæus of lodi150. for he would have it that "there is mutual work and mutual result, and therefore the motion is partly due to the attraction of the loadstone and partly to a spontaneous movement on the part of the iron: for as we say that vapours issuing from the loadstone hasten by their own nature to attract the iron, so also the air repelled by the vapours, whilst seeking a place for itself, is turned back, and when turned back, it impels the iron, lifts it up, as it were, and carries it along; the iron being of itself also excited somehow. so by being drawn out and by a spontaneous motion, and by striking against another substance, there is in some way produced a composite motion, which motion would nevertheless be rightly referred to attraction, because the terminus from which this motion invariably begins is the same terminus at which it ends, which is the characteristic proper of an attraction." there is certainly a mutual action, not an operation, nor does the loadstone attract in that way; nor is there any impulsion. but neither is there that origination of the motion by the vapours, and the turning of them back, which opinion of epicurus has so often been quoted by others. galen errs in his de naturalibus facultatibus, book i., chap. 14, when he expresses the view that whatever agents draw out either the venom of serpents or darts also exhibit the same power as the loadstone. now of what sort may be the attraction of such medicaments (if indeed it may be called attraction) we shall consider elsewhere. drugs against poisons or darts have no relation to, no similitude with, the action of magnetical bodies. the followers of galen (who hold that purgative medicaments attract because of similitude of substance) say that bodies are attracted on account of similitude, not identity, of substance; wherefore the loadstone draws iron, but iron does not draw iron. but we declare and prove that this happens in primary bodies, and in those bodies that are pretty closely related to them and especially like in kind one to another, on account of their identity; wherefore also loadstone draws loadstone and likewise iron iron; every really true earth draws earth; and iron fortified by a loadstone within the orbe of whose virtue it is placed draws iron more strongly than it does the loadstone. cardan asks why no other metal is attracted by any other stone; because (he replies) no metal is so cold as iron; as if indeed cold were the cause of the attraction, or as if iron were much colder than lead, which neither follows nor is deflected towards a loadstone. but that is a chilly story, and worse than an old woman's tale. so also is the notion that the loadstone is alive and that iron is its food. but how does the loadstone feed on the iron, when the filings in which it is kept are neither consumed nor become lighter? cornelius gemma, cosmographia, bk. x.151, holds that the loadstone draws iron to it by insensible rays, to which opinion he conjoins a story of a sucking fish and another about an antelope. guilielmus puteanus152 derives it, "not from any property of the whole substance unknown to any one and which cannot be demonstrated in any way (as galen, and after him almost all the physicians, have asserted), but from the essential nature of the thing itself, as if moving from the first by itself, and, as it were, by its own most powerful nature and from that innate temperament, as it were an instrument, which its substance, its effective nature uses in its operations, or a secondary cause and deprived of its intermediary"; so the loadstone attracts the iron not without a physical cause and for the sake of some good. but there is no such thing in other substances springing from some material form; unless it were primary, which he does not recognize. but certes good is shown to the loadstone by the stroke of the iron (as it were, association with a friend); yet it cannot either be discovered or conceived how that disposition may be the instrument of form. for what can temperament do in magnetical motions, which must be compared with the fixed, definite, constant motions of the stars, at great distances in case of the interposition of very dense and thick bodies? to baptista porta153 the loadstone seems a sort of mixture of stone and iron, in such a way that it is an iron stone or stony iron. "but i think" (he says) "the loadstone is a mixture of stone and iron, as an iron stone, or a stone of iron. yet do not think the stone is so changed into iron, as to lose its own nature, nor that the iron is so drowned in the stone, but it preserves itself; and whilst one labours to get the victory of the other, the attraction is made by the combat between them. in that body there is more of the stone than of iron; and therefore the iron, that it may not be subdued by the stone, desires the force and company of iron; that being not able to resist alone, it may be able by more help to defend itself. . . . the loadstone draws not stones, because it wants them not, for there is stone enough in the body of it; and if one loadstone draw another, it is not for the stone, but for the iron that is in it." as if in the loadstone the iron were a distinct body and not mixed up as the other metals in their ores! and that these, being so mixed up, should fight with one another, and should extend their quarrel, and that in consequence of the battle auxiliary forces should be called in, is indeed absurd. but iron itself, when excited by a loadstone, seizes iron no less strongly than the loadstone. therefore those fights, seditions, and conspiracies in the stone, as if it were nursing up perpetual quarrels, whence it might seek auxiliary forces, are the ravings of a babbling old woman, not the inventions of a distinguished mage. others have lit upon sympathy as the cause. there may be fellow-feeling, and yet the cause is not fellow-feeling; for no passion can rightly be said to be an efficient cause. others hold likeness of substance, many others insensible rays as the cause; men who also in very many cases often wretchedly misuse rays, which were first introduced in the natural sciences by the mathematicians. more eruditely does scaliger154 say that the iron moves toward the loadstone as if toward its parent, by whose secret principles it may be perfected, just as the earth toward its centre. the divine thomas155 does not differ much from him, when in the 7th book of his physica he discusses the reasons of motions. "in another way," he says, "it may be said to attract a thing, because it moves it to itself by altering it in some way, from which alteration it happens that when altered it moves according to its position, and in this manner the loadstone is said to attract iron. for as the parent moves things whether heavy or light, in as far as it gives them a form, by means of which they are moved to their place; so also the loadstone gives a certain quality to the iron, in accordance with which it moves towards it." this by no means ill-conceived opinion this most learned man shortly afterwards endeavoured to confirm by things which had obtained little credence respecting the loadstone and the adverse forces of garlick. cardinal cusan156 also is not to be despised. "iron has," he says, "in the loadstone a certain principle of its own effluence; and whilst the loadstone by its own presence excites the heavy and ponderous iron, the iron is borne by a wonderful yearning, even above the motion of nature (by which in accordance with its weight it ought to tend downwards) and moves upwards, in uniting itself with its own principle. for if there were not in the iron a certain natural foretaste of the loadstone itself, it would not move to the loadstone any more than to any other stone; and unless there were in the stone a greater inclination for iron than for copper, there would not be that attraction." such are the opinions expressed about the loadstone attracting (or the general sense of each), all dubious and untrustworthy. but those causes of the magnetical motions, which in the schools of the philosophers are referred to the four elements and the prime qualities, we relinquish to the moths and the worms.
