William Gilbert of Colchester, physician of London, On the magnet : magnetick bodies also, and on the great magnet the earth ; a new physiology, demonstrated by many arguments & experiments / William Gilbert.

  • Gilbert, William, 1544-1603.
Date:
1901
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Licence: In copyright

Credit: William Gilbert of Colchester, physician of London, On the magnet : magnetick bodies also, and on the great magnet the earth ; a new physiology, demonstrated by many arguments & experiments / William Gilbert. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    laying down a rule for fuch confiderable inequalities in the motion of the ftars, explained that the eighth fphere does not move with a continuous motion from weft to eaft ; but is ftiaken with a certain motion of trepidation, by which the firft points of Aries and Libra in the eighth heaven defcribe certain fmall circles with diameters equal to about nine degrees, around the firft points of Aries and Libra in the ninth fphere. But fince many things abfurd and impofiible as to motion follow from this motion of trepidation, that theory of motion is therefore long fince obfolete. Others there- fore are compelled to attribute the motion to the eighth fphere, and to eredt above it a ninth heaven alfo, yea, and to pile up yet a tenth and an eleventh : In the cafe of mathematicians, indeed, the fault may be condoned ; for it is permifiible for them, in the cafe of difficult motions, to lay down fome rule and law of equality by any hypothefes. But by no means can fuch enormous and monftrous celeftial ftrudtures be accepted by philofophers. And yet here one may fee how hard to pleafe are thofe who do not allow any motion to one very fmall body, the Earth ; and notwithftand- ing they drive and rotate the heavens, which are huge and immenfe above all conception and imagination: I declare that they feign the heavens to be three (the moft monftrous of all things in Nature) in order that fome obfcure motions forfooth may be accounted for. Ptolemy, who compares with his own the obfervations of Timocharis and Hipparchus, one of whom flouriffied 260 years, the other 460 years before him, thought that there was this motion of the eighth fphaere, and of the whole firmament; and proved by help of nu- merous phaenomena that it took place over the poles of the Zodiack, and, fuppofing its motion to be fo far equable, that the non-planetary ftars in the fpace of 100 years completed juft one degree beneath the Primum Mobile. After him 750 years Albategnius difcovered that one degree was completed in a fpace of 66 years, fo that a whole period would be 23,760 years. Alphonfus made out that this motion was ftill flower, completing one degree and 28 minutes only in 200 years ; and that thus the courfe of the fixed ftars went on, though unequally. At length Copernicus, by means of the obfervations of Timocharis, Ariftarchus of Samos, Hipparchus, Menelaus, Ptolemy, Mahometes Aradtenfis, Alphonfus, and of his own, detedted the anomalies of the motion of the Earth’s axis: though I doubt not that other anomalies alfo will come to light fome ages hence. So difficult is it to obferve motion fo flow, unlefs extending over a period of many centuries ; on which account we ftill fail to underftand the intent of Nature, what fhe is ftriving after through fuch inequality of motion. Let A be the pole of the Ecliptick, B C the Ecliptick, D the ^Equator; when the pole of the Earth near the ardtick circle of the Zodiack faces the point M, then there is an anomaly of the preceffion of the equinox at F; but