NOVUM ORGANUM. 345 



differentias novem. Primam, centri sui, circa quod corpora 

 mo vent ; secundam, polorum suorum, supra quos movent ; ter- 

 tiam, circumferentiae sive ambitus sui, prout distant a centre ; 

 quartam, incitationis suae, prout celerius aut tardius rotant; 

 quintam, consequutionis motus sui, veluti ab oriente in occiden- 

 tem, aut ab occidente in orientem ; sextam, declinationis a cir- 

 culo perfecto per spiras longius aut propius distantes a centro 

 suo; septimam, declinationis a circulo perfecto per spiras longius 

 aut propius distantes a polis suis ; octavam, distantias propioris 

 aut longioris spirarum suarum ad invicem ; nonam et ultirnam, 

 variationis ipsorum polorum, si sint mobiles ; quse ipsa ad rota- 

 tionem non pertinet, nisi fiat circulariter. 1 Atque iste motus 

 communi et inveterata opinione habetur pro proprio ccelestium. 

 Attamen gravis de illo motu lis est inter nonnullos tam ex an- 

 tiquis quam modernis, qui Rotationem terra? attribuerunt. At 

 multo fortasse justior movetur controversia (si modo res non sit 

 omnino extra controversiam), an motus videlicet iste (concesso 

 quod terra stet) coeli finibus contineatur, an potius descendat, 

 et communicetur aeri et aquis. Motum autem Rotationis in 

 missilibus, ut in spiculis, sagittis, pilis sclopetorum, et simili- 

 buSj omnino ad Motum Libertatis rejicimus. 



Sit Motus Decimus Octavus, Motus Trepidationis, cui (ut ab 

 astronomis intelligitur) non multum fidei adhibemus. 2 Nobis 



the eternal circular motions of the heavenly bodies may be subject, are sufficient to 

 destroy the whole a priori argument in favour of such a system of astronomy as that 

 which we find in the twelfth book of the Metaphysics. It has not been sufficiently 

 observed that the Ptolemaic system is no less at variance with the Peripatetic philo- 

 sophy than the heliocentrical. The attempts of Turrianus and Fracastorius to 

 construct what may be called an orthodox system of astronomy that is one in which 

 all the motions should take place in circles of which the earth is the centre was sug- 

 gested chiefly, as we learn from the Homocentrica of the latter, by the wish to reconcile 

 astronomy and philosophy. It had no scientific value, since it left all the phenomena 

 of variations of parallax and apparent diameter unexplained, or, at any rate, gave 

 an explanation of them which no astronomer would accept. It was nevertheless 

 favourably received by the systematic Peripaticians. See, for instance, Flaminius, 

 De prima Philusoph. Paraph, p. 119. (I quote the Basle edition of 1557.) 



1 1 believe the sense is that unless we restrict ourselves to circular motion, that is, 

 unless we reject the sixth and seventh species of variation, it will not be necessary for 

 us to suppose the poles themselves to be movable: in other words, that the phenomena 

 of which v;e could by this hypothesis give an account may be adequately represented 

 without it by means of spirals. 



a The name of trepidation was given by the Alphonsine astronomers to a motion 

 by which they imagined the starry heaven to be affected, and in virtue of which its 

 equinoxes described small circles of nine degrees radius about those of the .ninth or 

 next superior orb. To account for this motion they introduced a tenth orb. The 

 phenomenon, however, thus accounted for was altogether imaginary, although it is 

 true that the length of the tropical year, by supposed variations of which the idea of 

 trepidation was suggested, is not rigorously constant. It may be questioned whether 

 Bacon':- hesitation to accept the astronomical motion of trepidation had any better 

 foundation than his doubts whether the proper motions of the planetary orbs were 



