On the Magnet (原文阅读)

     著书立意乃赠花于人之举,然万卷书亦由人力而为,非尽善尽美处还盼见谅 !

                     —— 华辀远岑

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Chapter CXI

That the Earth moves circularly.

I f then the philosophers of the common sort, with an unspeakable absurdity, imagine the whole heaven and the vast extent of the universe to rotate in a whirl, it yet remains that the earth performs a diurnal change. For in no third way can the apparent revolutions be explained. This day, then, which is called natural, is a revolution of some meridian of the Earth from Sun to Sun. It revolves indeed in an entire course, from a fixed star round to that star again. Those bodies which in nature are moved with a circular, æquable and constant motion, are furnished, in their parts, with various boundaries. But the Earth is not a Chaos nor disordered mass; but by reason of its astral virtue, it has boundaries which subserve the circular motion, poles not mathematical, an æquator not devised by imagination, meridians also and parallels; all of which we find permanent, certain and natural in the Earth: which by numerous experiments the whole magnetick philosophy sets forth. For in the earth there are poles set in fixed bounds, and at them the verticity mounts up on either side from the plane of the Earth's æquator, with forces which are mightier and præpotent from the common action of the whole; and with these poles the diurnal revolution is in agreement. But in no turnings-about of bodies, in none of the motions of the planets are there to be recognized, beheld, or assured to us by any reasoning any sensible or natural poles in the firmament, or in any Primum Mobile; but those are the conception of an unsettled imagination. Wherefore we, following an evident, sensible and tested cause, do know that the earth moves on its own poles, which are apparent to us by many magnetick demonstrations. For not only on the ground of its constancy, and its sure and permanent position, is the Earth endowed with poles and verticity: for it might be directed toward other parts of the universe, toward East or West or some other region. By the wondrous wisdom then of the Builder forces, primarily animate, have been implanted in the Earth, that with determinate constancy the Earth may take its direction, and the poles have been placed truly opposite246, that about them as the termini, as it were, of some axis, the motion of diurnal turning might be performed. But the constancy of the poles is regulated by the primary soul. Wherefore, for the Earth's good, the collimations of her verticities do not continually regard a definite point of the firmament and of the visible heaven. For

changes of the æquinoxes take place from a certain deflection of the Earth's axis; yet in regard to that deflection, the Earth has a constancy of motion derived from her own forces. The Earth, that she may turn herself about in a diurnal revolution, leans on her poles. For since at A and B there is constant verticity, and the axis is straight; at C and D (the æquinoctial line) the parts are free, the whole forces on either side being spread out from the plane of the æquator toward the poles, in æther which is free from renitency, or else in a void; and A and B remaining constant, C revolves toward D both from innate conformity and aptitude, and for necessary good, and the avoidance of evil; but being chiefly moved forward by the diffusion of the solar orbes of virtues, and by their lights. And 'tis borne around, not upon a new and strange course, but (with the tendency common to the rest of the planets) it tends from West to East. For all planets have a like motion Eastward according to the succession of the signs, whether Mercury and Venus revolve beneath the Sun, or around the Sun. That the Earth is capable of and fitted for moving circularly its parts show, which when separated from the whole are not only borne along with the straight movement taught by the Peripateticks, but rotate also. A loadstone fixed in a wooden vessel is placed on water so as to swim freely, turn itself, and float about. If the pole B of the loadstone be set contrary to nature toward the South, F, the Terrella is turned about its own centre with a circular motion in the plane of the Horizon, toward the North, E, where it rests, not at C or D. So does a small stone if only of four ounces; it has the same motion also and just as quick, if it were a strong magnet of one hundred pounds. The largest magnetical mountain will possess the same turning-power also, if launched in a wide river or deep sea: and yet a magnetick body is much more hindered by water than the whole Earth is by the æther. The whole Earth would do the same, if the Boreal pole were to be diverted from its true direction; for the Boreal pole would run back with the circular motion of the whole around the centre toward the Cynosure. But this motion by which the parts naturally settle themselves in their own resting-places is no other than circular. The whole Earth regards the Cynosure with her pole according to a steadfast law of her nature: and thus each true part of it seeks a like resting-place in the world, and is moved circularly toward that position. The natural movements of the whole and of the parts are alike: wherefore when the parts are moved in a circle, the whole also has the potency of moving circularly. A sphærical loadstone placed in a vessel on water moves circularly around its centre (as is manifest) in the plane of the Horizon, into conformity with the earth.

So also it would move in any other great circle if it could be free; as in the declination instrument, a circular motion takes place in the meridian (if there were no variation), or, if there should be some variation, in a great circle drawn from the Zenith through the point of variation on the horizon. And that circular motion of the magnet to its own just and natural position shows that the whole Earth is fitted and adapted, and is sufficiently furnished with peculiar forces for diurnal circular motion. I omit what Peter Peregrinus constantly affirms, that a terrella suspended above its poles on a meridian moves circularly, making an entire revolution in 24 hours: which, however, it has not happened to ourselves as yet to see; and we even doubt this motion on account of the weight of the stone itself, as well as because the whole Earth, as she is moved of herself, so also is she propelled by other stars: and this does not happen in proportion (as it does in the terrella) in every part. The Earth is moved by her own primary form and natural desire, for the conservation, perfection, and ordering of its parts, toward things more excellent: and this is more likely than that the fixed stars, those luminous globes, as well as the Wanderers, and the most glorious and divine Sun, which are in no way aided by the Earth, or renewed, or urged by any virtue therein, should circulate aimlessly around the Earth, and that the whole heavenly host should repeat around the Earth courses never ending and of no profit whatever to the stars. The Earth, then, which by some great necessity, even by a virtue innate, evident, and conspicuous, is turned circularly about the Sun, revolves; and by this motion it rejoices in the solar virtues and influences, and is strengthened by its own sure verticity, that it should not rovingly revolve over every region of the heavens. The Sun (the chief agent in nature) as he forwards the courses of the Wanderers, so does he prompt this turning about of the Earth by the diffusion of the virtues of his orbes, and of light. And if the Earth were not made to spin with a diurnal revolution, the Sun would ever hang over some determinate part with constant beams, and by long tarriance would scorch it, and pulverize it, and dissipate it, and the Earth would sustain the deepest wounds; and nothing good would issue forth; it would not vegetate, it would not allow life to animals, and mankind would perish. In other parts, all things would verily be frightful and stark with extreme cold; whence all high places would be very rough, unfruitful, inaccessible, covered with a pall of perpetual shades and eternal night. Since the Earth herself would not choose to endure this so miserable and horrid appearance on both her faces, she, by her magnetick astral genius, revolves in an orbit, that by a perpetual change of light there may be a perpetual alternation of things, heat and cold, risings and settings, day and night, morn and eve, noon and midnight. Thus the Earth seeks and re-seeks the Sun, turns away from him and pursues him, by her own wondrous magnetick virtue. Besides, it is not only from the Sun that evil would impend, if the Earth were to stay still and be deprived of solar benefit; but from the Moon also serious dangers would threaten. For we see how the ocean rises and swells beneath certain known positions of the Moon: And if there were not through the daily rotation of Earth a speedy transit of the Moon, the flowing sea would be driven above its level into certain regions, and many shores would be overwhelmed with huge waves. In order then that Earth may not perish in various ways, and be brought to confusion, she turns herself about by magnetick and primary virtue: and the like motions exist also in the rest of the Wanderers, urged specially by the movement and light of other bodies. For the Moon also turns herself about in a monthly course, to receive in succession the Sun's beams in which she, like the Earth, rejoices, and is refreshed: nor could she endure them for ever on one particular side without great harm and sure destruction. Thus each one of the moving globes is for its own safety borne in an orbit either in some wider circle, or only by a rotation of its body, or by both together. But it is ridiculous for a man a philosopher to suppose that all the fixed stars and the planets and the still higher heavens revolve to no other purpose, save the advantage of the Earth. It is the Earth, then, that revolves, not the whole heaven, and this motion gives opportunity for the growth and decrease of things, and for the generating of things animate, and awakens internal heat for the bringing of them to birth. Whence matter is quickened for receiving forms; and from the primary rotation of the Earth natural bodies have their primary impetus and original activity. The motion then of the whole Earth is primary, astral, circular, around its own poles, whose verticity arises on both sides from the plane of the æquator, and whose vigour is infused into opposite termini, in order that the Earth may be moved by a sure rotation for its good, the Sun also and the stars helping its motion. But the simple straight motion downwards of the Peripateticks is a motion of weight, a motion of the aggregation of disjoined parts, in the ratio of their matter, along straight lines toward the body of the Earth: which lines tend the shortest way toward the centre. The motions of disjoined magnetical parts of the Earth, besides the motion of aggregation, are coition, revolution, and the direction of the parts to the whole, for harmony of form, and concordancy.

Chapter CXII

Arguments of those denying the Earth's motion, and their confutation.

N ow it will not be superfluous to weigh well the arguments of those who say the Earth does not move; that we may be better able to satisfy the crowd of philosophizers who assert that this constancy and stability of the Earth is confirmed by the most convincing arguments. Aristotle does not allow that the Earth moves circularly, on the ground that each several part of it would be affected by this particular motion; that whereas now all the separate parts of the Earth are borne toward the middle in straight lines, that circular motion would be violent, and strange to nature, and not enduring. But it has been before proved that all actual portions of the Earth move in a circle, and that all magnetick bodies (fitly disposed) are borne around in an orbe. They are borne, however, toward the centre of the Earth in a straight line (if the way be open) by a motion of aggregation as though to their own origin: they move by various motions agreeably to the conformation of the whole: a terrella is moved circularly by its innate forces. "Besides" (says he), "all things which are borne in an orbe, afterwards would seem to be abandoned by the first motion, and to be borne by several motions besides the first. The Earth must also be borne on by two sorts of motion, whether it be situate around a mid-point, or in the middle site of the universe: and if this were so, there must needs be at one time an advance, at another time a retrogression of the fixed stars: This, however, does not seem to be the case, but they rise and set always the same in the same places." But it by no means follows that a double motion must be assigned to the Earth. But if there be but one diurnal motion of the Earth around its poles, who does not see that the stars must always in the same manner rise and set at the same points of the horizon, even although there be another motion about which we are not disputing: since the mutations in the smaller orbit cause no variation of aspect in the fixed stars owing to their great distance, unless the axis of the Earth have varied its position, concerning which we raise a question when speaking of the cause of the præcession of the æquinoxes. In this argument are many flaws. For if the Earth revolve, that we asserted must needs occur not by reason of the first sphære, but of its innate forces. But if it were set in motion by the first sphære, there would be no successions of days and nights, for it would continue its course along with the Primum Mobile. But that the Earth is affected by a double movement at the time when it rotates around its own centre, because the rest of the stars move with a double motion, does not follow. Besides, he does not well consider the argument, nor do his interpreters understand the same. τούτου δὲ συμβαίνοντος, ἀναγκαῖον γίγνεσθαι παρόδους καὶ τροπὰς τῶν ἐνδεδεμένων ἄστρων. (Arist. de Cœlo, ii. chap. 14.) That is, "If this be so, there must needs be changes, and retrogressions of the fixed stars." What some interpret as retrogressions or regressions, and changes of the fixed stars, others explain as diversions: which terms can in no way be understood of axial motion, unless he meant that the Earth moved by the Primum Mobile is borne and turned over other poles diverse even from those which correspond to the first sphære, which is altogether absurd. Other later theorists suppose that the eastern ocean ought to be impelled so into western regions by that motion, that those parts of the Earth which are dry and free from water would be daily flooded by the eastern ocean. But the ocean is not acted upon by that movement, since nothing opposes it; and even the whole atmosphere is carried round: And for that reason in the Earth's course all the things in the air are not left behind by us nor do they seem to move toward the West: Wherefore also the clouds are at rest in the air, unless the force of the winds drive them; and objects which are projected into the air fall again into their own place. But those foolish folk who think that towers, temples, and buildings must necessarily be shaken and overthrown by the Earth's motion, may fear lest men at the Antipodes should slip off into an opposite orbe, or that ships when sailing round the entire 249globe should (as soon as they have dipped under the plane of our horizon) fall into the opposite region of the sky. But those follies are old wives' gossip, and the rubbish of certain philosophizers, men who, when they essay to treat of the highest truths and the fabrick of the universe, and hazard anything, can scarce understand aught ultra crepidam. They would have the Earth to be the centre of a circle; and therefore to rest motionless amid the rotation. But neither the stars nor the wandering globes move about the Earth's centre: the high heaven also does not move circularly round the Earth's centre; nor if the Earth were in the centre, is it a centre itself, but a body around a centre. Nor is it confident with reason that the heavenly bodies of the Peripateticks should attend on a centre so decadent and perishable as that of the Earth. They think that Nature seeks rest for the generation of things, and for promoting their increase while growing; and that accordingly the whole Earth is at rest. And yet all generation takes place from motion, without which the universal nature of things would become torpid. The motion of the Sun, the motion of the Moon, cause changes; the motion of the Earth awakens the internal breath of the globe; animals themselves do not live without motion, and the ceaseless activity of the heart and arteries. For of no moment are the arguments for a simple straight motion toward the centre, that this is the only kind in the Earth, and that in a simple body there is one motion only and that a simple one. For that straight motion is only a tendency toward their own origin, not of the parts of the Earth only, but of those of the Sun also, of the Moon, and of the rest of the sphæres which also move in an orbit. Joannes Costæus, who raises doubts concerning the cause of the Earth's motion, looking for it externally and internally, understands magnetick vigour to be internal, active, and disponent; also that the Sun is an external promotive cause, and that the Earth is not so vile and abject a body as it is generally considered. Accordingly there is a diurnal movement on the part of the Earth for its own sake and for its advantage. Those who make out that that terrestrial motion (if such there be) takes place not only in longitude, but also in latitude, talk nonsense. For Nature has set in the Earth determinate poles, and definite unconfused revolutions. Thus the Moon revolves with respect to the Sun in a monthly course; yet having her own definite poles, facing determinate parts of the heaven. To suppose that the air moves the Earth would be ridiculous. For air is only exhalation, and is an enveloping effluvium from the Earth itself; the winds also are only a rush of the exhalations in some part near the Earth's surface; the height of its motion is slight, and in all regions there are various winds unlike and contrary. Some writers, not finding in the matter of the Earth the cause (for they say that they find nothing except solidity and consistency), deny it to be in its form; and they only admit as qualities of the Earth cold and dryness, which are unable to move the Earth. The Stoicks attribute a soul to the Earth, whence they pronounce (amid the laughter of the learned) the Earth to be an animal. This magnetick form, whether vigour or soul, is astral. Let the learned lament and bewail the fact that none of those old Peripateticks, nor even those common philosophizers heretofore, nor Joannes Costæus, who mocks at such things, were able to apprehend this grand and important natural fact. But as to the notion that surface inequality of mountains and valleys would prevent the Earth's diurnal revolution, there is nothing in it: for they do not mar the Earth's roundness, being but slight excrescences compared with the whole Earth; nor does the Earth revolve alone without its emanations. Beyond the emanations, there is no renitency. There is no more labour exerted in the Earth's motion than in the march of the rest of the Stars: nor is it excelled in dignity by some stars. To say that it is frivolous to suppose that the Earth rather seeks a view of the Sun, than the Sun of the Earth, is a mark of great obstinacy and unwisdom. Of the theory of the rotation we have often spoken. If anyone seek the cause of the revolution, or of other tendency of the Earth, from the sea surrounding it, or from the motion of the air, or from the Earth's gravity, he would be no less silly as a theorist than those who stubbornly ground their opinions on the sentiments of the ancients. Ptolemy's reasonings are of no weight; for when our true principles are laid down, the truth comes to light, and it is superfluous to refute them. Let Costæus recognize and philosophers see how unfruitful and vain a thing it becomes then to take one's stand on the principles and unproved opinions of certain ancients. Some raise a doubt how it can be that, if the Earth move round its own axis, a globe of iron or of lead dropped from the highest point of a tower falls exactly perpendicularly to a spot of the Earth below itself. Also how it is that cannon balls from a large culverin, fired with the same quantity and strength of powder, in the same direction and at a like elevation through the same air, would be cast at a like distance from a given spot both Eastward and Westward, supposing the Earth to move Eastward. But those who bring forward this kind of argument are being misled: not attending to the nature of primary globes, and the combination of parts with their globes, even though they be not adjoined by solid parts. Whereas the motion of the Earth in the diurnal revolution does not involve the separation of her more solid circumference from the surrounding bodies; but all her effluvia surround her, and in them heavy bodies projected in any way by force, move on uniformly along with the Earth in general coherence. And this also takes place in all primary bodies, the Sun, the Moon, the Earth, the parts betaking themselves to their first origins and sources, with which they connect themselves with the same appetence as terrene things, which we call heavy, with the Earth. So lunar things tend to the Moon, solar things to the Sun, within the orbes of their own effluvia. The emanations hold together by continuity of substance, and heavy bodies are also united with the Earth by their own gravity, and move on together in the general motion: especially when there is no renitency of bodies in the way. And for this cause, on account of the Earth's diurnal revolution, bodies are neither set in motion, nor retarded; they do not overtake it, nor do they fall short behind it when violently projected toward East or West.

Let E F G be the Earth's globe, A its centre, L E the ascending effluvia: Just as the orbe of the effluvia progresses with the Earth, so also does the unmoved part of the circle at the straight line L E progress along with the general revolution. At L and E, a heavy body, M, falls perpendicularly toward E, taking the shortest way to the centre, nor is that right movement of weight, or of aggregation compounded with a circular movement, but is a simple right motion, never leaving the line L E. But when thrown with an equal force from E toward F, and from E toward G, it completes an equal distance on either side, even though the daily rotation of the Earth is in process: just as twenty paces of a man mark an equal space whether toward East or West: so the Earth's diurnal motion is by no means refuted by the illustrious Tycho Brahe, through arguments such as these.

The tendency toward its origin (which, in the case of the Earth, is called by Philosophers weight) causes no resistance to the diurnal revolution, nor does it direct the Earth, nor does it retain the parts of the Earth in place, for in regard to the Earth's solidity they are imponderous, nor do they incline further, but are at rest in the mass. If there be a flaw in the mass, such as a deep cavity (say 1000 fathoms), a homogenic portion of the Earth, or compacted terrestrial matter, descends through that space (whether filled with water or air) toward an origin more assured than air or water, seeking a solid globe. But the centre of the Earth, as also the Earth as a whole, is imponderous; the separated parts tend toward their own origin, but that tendency we call weight; the parts united are at rest; and even if they were ponderable, they would introduce no hindrance to the diurnal revolution. For if around the axis A B, there be a weight at C, it is balanced from E; if at F, from G; if at H, from I. So internally at L, they are balanced from M: the whole globe, then, having a natural axis, is balanced in æquilibrio, and is easily set in motion by the slighted cause, but especially because the Earth in her own place is nowise heavy nor lacking in balance. Therefore weight neither hinders the diurnal revolution, nor influences either the direction or continuance in position. Wherefore it is manifest that no sufficiently strong reason has yet been found out by Philosophers against the motion of the Earth.

Chapter CXIII

On the cause of the definite time, of an entire rotation of the Earth.

D iurnal motion is due to causes which have now to be sought, arising from magnetick vigour and from the confederated bodies; that is to say, why the diurnal rotation of the Earth is completed in the space of twenty-four hours. For no curious art, whether of Clepsydras or of sand-clocks, or those contrivances of little toothed wheels which are set in motion by weights, or by the force of a bent steel band, can discover any degree of difference in the time. But as soon as the diurnal rotation has been gone through, it at once begins over again. But we would take as the day the absolute turning of a meridian of the Earth, from sun to sun. This is somewhat greater than one whole revolution of it; in this way the yearly course is completed in 365 and nearly ¼ turnings with respect to the sun. From this sure and regular motion of the Earth, the number and time of 365 days, 5 hours, 55 minutes, in solar tropical years is always certain and definite, except that there are some slight differences due to other causes. The Earth therefore revolves not fortuitously, or by chance, or precipitately; but with a rather high intelligence, equably, and with a wondrous regularity, in no other way than all the rest of the movable stars, which have definite periods belonging to their motions. For the Sun himself being the agent and incitor of the universe in motion, other wandering globes set within the range of his forces, when acted on and stirred, also regulate each its own proper courses by its own forces; and they are turned about in periods corresponding to the extent of their greater rotation, and the differences of their effused forces, and their intelligence for higher good. And for that cause Saturn, having a wider orbit, is borne round it in a longer time, Jupiter a shorter, and Mars still less; while Venus takes nine months, Mercury 80 days, on the hypotheses of Copernicus; the Moon going round the Earth with respect to the Sun in 29 days, 12 hours, 44 minutes. We have asserted that the Earth moves circularly about its centre, completing a day by an entire revolution with respect to the Sun. The Moon revolves in a monthly course around the Earth, and, repeating a conjunction with the Sun after a former synodic conjunction, constitutes the month or Lunar day. The Moon's mean concentrick orbit, according to numerous observations of Copernicus and later astronomers, is found to be distant 29 and about 5/6 diameters of the Earth from the Earth's centre. The Moon's revolution with respect to the Sun takes place in 29½ days and 44 minutes of time. We reckon the motion with respect to the sun, not the periodic motion, just as a day is one entire revolution of the Earth with respect to the Sun, not one periodick revolution; because the Sun is the cause of lunar as of terrestrial motion: also, because (on the hypotheses of later observers) the synodical month is truly periodic, on account of the Earth's motion in a great orbit. The proportion of diameters to circumferences is the same. And the concentrick orbit of the Moon contains twice over 29 and ½ great circles of the Earth & a little more. The Moon & the Earth, then, agree together in a double proportion of motion; & the Earth moves in the space of twenty-four hours, in its diurnal motion; because the Moon has a motion proportional to the Earth, but the Earth a motion agreeing with the lunar motion in a nearly double proportion. There is some difference in details, because the distances of the stars in details have not been examined sufficiently exactly, nor are mathematicians as yet agreed about them. The Earth therefore revolves in a space of 24 hours, as the Moon in her monthly course, by a magnetick confederation of both stars, the globes being forwarded in their movement by the Sun, according to the proportion of their orbits, as Aristotle allows, de Cœlo, bk. ii., chap. 10. "It happens" (he says) "that the motions are performed through a proportion existing between them severally, namely, at the same intervals in which some are swifter, others slower," But it is more agreeable to the relation between the Moon and the Earth, that that harmony of motion should be due to the fact that they are bodies rather near together, and very like each other in nature and substance, and that the Moon has more evident effects upon the Earth than the rest of the stars, the Sun excepted; also because the Moon alone of all the planets conducts her revolutions, directly (however diverse even), with reference to the Earth's centre, and is especially akin to the Earth, and bound to it as with chains. This, then, is the true symmetry and harmony between the motions of the Earth and the Moon; not that old oft-besung harmony of cœlestial motions, which assumes that the nearer any sphære is to the Primum Mobile and that fictitious and pretended rapidest Prime Motion, the less does it offer resistance thereto, and the slower it is borne by its own motion from west to east: but that the more remote it is, the greater is its velocity, and the more freely does it complete its own movement; and therefore that the Moon (being at the greatest distance from the Primum Mobile) revolves the most swiftly. Those vain tales have been conceded in order that the Primum Mobile may be accepted, and be thought to have certain effects in retarding the motions of the lower heavens; as though the motion of the stars arose from retardation, and were not inherent and natural; and as though a furious force were perpetually driving the rest of the heaven (except only the Primum Mobile) with frenzied incitations. Much more likely is it that the stars are borne around symmetrically by their own forces, with a certain mutual concert and harmony.

Chapter CXIV

On the primary magnetick nature of the Earth, whereby its poles are parted from the poles of the Ecliptick.

P rimarily having shown the manner and causes of the diurnal revolution of the Earth, which is partly brought about from the vigour of the magnetick virtue, partly effected by the præ-eminence and light of the Sun; there now follows an account of the distance of its poles from the poles of the Ecliptick — a supremely necessary fact. For if the poles of the universe or of the Earth remained fast at the poles of the Zodiack, then the Æquator of the Earth would lie exactly beneath the line of the Ecliptick, and there would be no variation in the seasons of the year, no Winter, no Summer, nor Spring, nor Autumn: but one and the same invariable aspect of things would continue. The direction of the axis of the Earth has receded therefore from the pole of the Zodiack (for lasting good) just so far as is sufficient for the generation and variety of things. Accordingly the declination of the tropicks and the inclination of the Earth's pole remain perpetually in the twenty-fourth degree; though now only 23 degrees 28 minutes are counted; or, as others make out, 29 minutes: But once it was 23 degrees 52 minutes, which are the extreme limits of the declinations hitherto observed. And that has been prudently ordained by nature, and is arranged by the primary excellence of the Earth. For if those poles (of the Earth and the Ecliptick) were to be parted by a much greater distance, then when the Sun approached the tropick, all things in the other deserted part of the globe, in some higher latitude, would be desolate and (by reason of the too prolonged absence of the Sun) brought to destruction. As it is, however, all is so proportioned that the whole terrestrial globe has its own varying seasons in succession, and alternations of condition, appropriate and needful: either from the more direct and vertical radiation of light, or from its increased tarriance above the horizon.

Around these poles of the Ecliptick the direction of the poles of the Earth is borne: and by this motion the præcession of the æquinoxes is apparent to us.

Chapter CXV

On the Præcession of the Æquinoxes, from the magnetick motion of the poles of the Earth, in the Arctick and Antarctick circle of the Zodiack.

P rimitive mathematicians, since they did not pay attention to the inequælities of the years, made no distinction between the æquinoctial, or solstitial revolving year, and that which is taken from some one of the fixed stars. Even the Olympick years, which they used to reckon from the rising of the dogstar, they thought to be the same as those counted from the solstice. Hipparchus of Rhodes was the first to call attention to the fact that these differ from each other, and discovered that the year was longer when measured by the fixed stars than by the æquinox or solstice: whence he supposed that there was in the fixed stars also some motion in a common sequence; but very slow, and not at once perceptible. After him Menelaus, a Roman geometer, then Ptolemy, and long afterward Mahometes Aractensis, and several more, in all their literary memoirs, perceived that the fixed stars and the whole firmament proceeded in an orderly sequence, regarding as they did the heaven, not the earth, and not understanding the magnetical inclinations. But we shall demomstrate that it proceeds rather from a certain rotatory motion of the Earth's axis, than that that eighth sphære (so called) the firmament, or non-moving empyrean, revolves studded with innumerable globes and stars, whose distances from the Earth have never been proved by anyone, nor can be proved (the whole universe gliding, as it were). And surely it should seem much more likely that the appearances in the heavens should be clearly accounted for by a certain inflection and inclination of the comparatively small body of the Earth, than by the setting in motion of the whole system of the universe; especially if this motion is to be regarded as ordained solely for the Earth's advantage: While for the fixed stars, or for the planets, it is of no use at all. For this motion the rising and settings of stars in every Horizon, as well as their culminations at the height of the heavens, are shifted so much that the stars which once were vertical are now some degrees distant from the zenith. For nature has taken care, through the Earth's soul or magnetick vigour, that, just as it was needful in tempering, receiving, and warding off the sun's rays and light, by suitable seasons, that the points toward which the Earth's pole is directed should be 23 degrees and more from the poles of the Ecliptick250: so now for moderating and for receiving the luminous rays of the fixed stars in due turn and succession, the Earth's poles should revolve at the same distance from the Ecliptick at the Ecliptick's arctick circle; or rather that they should creep at a gentle pace, that the actions of the stars should not always remain at the same parallel circles, but should have a rather slow mutation. For the influences of the stars are not so forceful as that a swifter course should be desired. Slowly, then, is the Earth's axis inflected; and the stars' rays, falling upon the face of the Earth, shift only in so long a time as a diameter of the arctick or polar circle is extended: whence the star at the extremity of the tail of the Cynosure, which once was 12 degrees 24 minutes (namely, in the time of Hipparchus) distant from the pole of the universe, or from that point which the pole of the Earth used to face, is now only 2 degrees and 52 minutes distant from the same point; whence from its nearness it is called by the moderns Polaris. Some time it will be only ½ degree away from the pole: afterward it will begin to recede from the pole until it will be 48 degrees distant; and this, according to the Prutenical tables, will be in Anno Domini 15000. Thus Lucida Lyræ (which to us southern Britons now almost culminates) will some time approach to the pole of the world, to about the fifth degree. So all the stars shift their rays of light at the surface of the Earth, through this wonderful magnetical inflection of the Earth's axis. Hence come new varieties of the seasons of the year, and lands become more fruitful or more barren; hence the characters and manners of nations are changed; kingdoms and laws are altered, in accordance with the virtue of the fixed stars as they culminate, and the strength thence received or lost in accordance with the singular and specifick nature of each; or on account of new configurations with the planets in other places of the Zodiack; on account also of risings and settings, and of new concurrences at the meridian. The Præcession of the æquinoxes arising from the aequable motion of the Earth's pole in the arctick circle of the Zodiack is here demonstrated. Let A B C D be the Ecliptick line; I E G the arctic circle of the Zodiack. Then if the Earth's pole look to E, the æquinoxes are at D, C. Let this be at the time of Metho, when the horns of Aries were in the æquinoctial colure. Now if the Earth's pole have advanced to I; then the æquinoxes will be at K, L; and the stars in the ecliptick C will seem to have progressed, in the order of the signs, along the whole arc K C: L will be moved on by the præcession, against the order of the signs, along the arc D L. But this would occur in the contrary order, if the point G were to face the poles of the earth, and the motion were from E to G: for then the æquinoxes would be M N, and the fixed stars would anticipate the same at

C and D, counter to the order of the signs.

Chapter CXVI

On the anomaly of the Præcession of the Equinoxes, and of the obliquity of the Zodiack.

A t one time the shifting of the æquinoxes is quicker, at another slower, being not always equal: because the poles of the earth travel unequally in the arctick and antarctick circle of the Zodiack; and decline on both sides from the middle path: whence the obliquity of the Zodiack to the Æquator seems to change. And as this has become known by means of long observations, so also has it been perceived, that the true æquinoctial points have been elongated from the mean æquinoctial points, on this side and on that, by 70 minutes (when the prostaphæresis is greatest): but that the solstices either approach the equator unequally 12 minutes nearer, or recede as far behind; so that the nearest approach is 23 degrees 28 minutes, and the greatest elongation 23 degrees 52 minutes. Astronomers have given various explanations to account for this inequality of the præcession and also of the obliquity of the tropicks. Thebit, with the view of laying down a rule for such considerable inequalities in the motion of the stars, explained that the eighth sphære does not move with a continuous motion from west to east; but is shaken with a certain motion of trepidation, by which the first points of Aries and Libra in the eighth heaven describe certain small circles with diameters equal to about nine degrees, around the first points of Aries and Libra in the ninth sphære. But since many things absurd and impossible as to motion follow from this motion of trepidation, that theory of motion is therefore long since obsolete. Others therefore are compelled to attribute the motion to the eighth sphære, and to erect above it a ninth heaven also, yea, and to pile up yet a tenth and an eleventh: In the case of mathematicians, indeed, the fault may be condoned; for it is permissible for them, in the case of difficult motions, to lay down some rule and law of equality by any hypotheses. But by no means can such enormous and monstrous celestial structures be accepted by philosophers. And yet here one may see how hard to please are those who do not allow any motion to one very small body, the Earth; and notwithstanding they drive and rotate the heavens, which are huge and immense above all conception and imagination: I declare that they feign the heavens to be three (the most monstrous of all things in Nature) in order that some obscure motions forsooth251 may be accounted for. Ptolemy, who compares with his own the observations of Timocharis and Hipparchus, one of whom flourished 260 years, the other 460 years before him, thought that there was this motion of the eighth sphære, and of the whole firmament; and proved by help of numerous phenomena that it took place over the poles of the Zodiack, and, supposing its motion to be so far æquable, that the non-planetary stars in the space of 100 years completed just one degree beneath the Primum Mobile. After him 750 years Albategnius discovered that one degree was completed in a space of 66 years, so that a whole period would be 23,760 years. Alphonsus made out that this motion was still slower, completing one degree and 28 minutes only in 200 years; and that thus the course of the fixed stars went on, though unequally. At length Copernicus, by means of the observations of Timocharis, Aristarchus of Samos, Hipparchus, Menelaus, Ptolemy, Mahometes Aractensis, Alphonsus, and of his own, detected the anomalies of the motion of the Earth's axis: though I doubt not that other anomalies also will come to light some ages hence. So difficult is it to observe motion so slow, unless extending over a period of many centuries; on which account we still fail to understand the intent of Nature, what she is driving after through such inequality of motion. Let A be the pole of the Ecliptick, B C the Ecliptick, D the Æquator; when the pole of the Earth near the arctick circle of the Zodiack faces the point M, then there is an anomaly of the præcession of the æquinox at F; but when it faces N, there is an anomaly of the præcession at E. But when it faces I directly, then the maximum obliquity G is observed at the solstitial colure; but when it faces L, there is

the minimum obliquity H at the solstitial colure.

Copernicus' contorted circlet in the Arctick circle of the Zodiack.

Let F B G be the half of the Arctick circle described round the pole of the Zodiack: A B C the solstitial colure: A the pole of the Zodiack; D E the anomaly of longitude 140 minutes at either side on both ends: B C the anomaly of obliquity 24 minutes: B the greater obliquity of 23 degrees 52 minutes: D the mean obliquity of 23 degrees 40 minutes: C the minimum obliquity of 23 degrees 28 minutes.

The period of motion of the præcession of the æquinoxes is 25,816 Ægyptian years; the period of the obliquity of the Zodiack is 3434 years, and a little more. The period of the anomaly of the præcession of the æquinoxes is 1717 years, and a little more. If the whole time of the motion AI were divided into eight equal parts: in the first eighth the pole is borne somewhat swiftly from A to B; in the second eighth, more slowly from B to C; in the third, with the same slowness from C to D; in the fourth, more swiftly again from D to E; in the fifth, with the same swiftness from E to F; again more slowly from F to G; and with the same slowness from G to H; in the last eighth, somewhat swiftly again from H to I. And this is the contorted circlet of Copernicus, fused with the mean motion into the curved line which is the path of the true motion. And thus the pole attains the period of the anomaly of the præcession of the æquinoxes twice; and that of the declination or obliquity once only. It is thus that by later astronomers, but especially by Copernicus (the Restorer of Astronomy)252, the anomalies of the motion of the Earth's axis are described, so far as the observations of the ancients down to our own times admit; but there are still needed more and exact observations for anyone to establish aught certain about the anomaly of the motion of the præcessions, and at the same time that also of the obliquity of the Zodiack. For ever since the time at which, by means of various observations, this anomaly was first observed, we have only arrived at half a period of the obliquity. So that all the more all these matters about the unequal motion both of the præcession and of the obliquity are uncertain and not well known: wherefore neither can we ourselves assign any natural causes for it, and establish it for certain. Wherefore also do we to our reasonings and experiments magnetical here set an end and period.253

FINIS

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