on the heavens-第15章
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melodious and poetical as the theory is； it cannot be a true account of the facts。 There is not only the absurdity of our hearing nothing； the ground of which they try to remove； but also the fact that no effect other than sensitive is produced upon us。 Excessive noises； we know； shatter the solid bodies even of inanimate things： the noise of thunder； for instance； splits rocks and the strongest of bodies。 But if the moving bodies are so great； and the sound which penetrates to us is proportionate to their size； that sound must needs reach us in an intensity many times that of thunder； and the force of its action must be immense。 Indeed the reason why we do not hear； and show in our bodies none of the effects of violent force； is easily given： it is that there is no noise。 But not only is the explanation evident； it is also a corroboration of the truth of the views we have advanced。 For the very difficulty which made the Pythagoreans say that the motion of the stars produces a concord corroborates our view。 Bodies which are themselves in motion； produce noise and friction： but those which are attached or fixed to a moving body； as the parts to a ship； can no more create noise； than a ship on a river moving with the stream。 Yet by the same argument one might say it was absurd that on a large vessel the motion of mast and poop should not make a great noise； and the like might be said of the movement of the vessel itself。 But sound is caused when a moving body is enclosed in an unmoved body； and cannot be caused by one enclosed in； and continuous with； a moving body which creates no friction。 We may say； then； in this matter that if the heavenly bodies moved in a generally diffused mass of air or fire； as every one supposes； their motion would necessarily cause a noise of tremendous strength and such a noise would necessarily reach and shatter us。 Since； therefore； this effect is evidently not produced； it follows that none of them can move with the motion either of animate nature or of constraint。 It is as though nature had foreseen the result； that if their movement were other than it is； nothing on this earth could maintain its character。 That the stars are spherical and are not selfmoved； has now been explained。
10
With their order…I mean the position of each； as involving the priority of some and the posteriority of others； and their respective distances from the extremity…with this astronomy may be left to deal； since the astronomical discussion is adequate。 This discussion shows that the movements of the several stars depend； as regards the varieties of speed which they exhibit； on the distance of each from the extremity。 It is established that the outermost revolution of the heavens is a simple movement and the swiftest of all； and that the movement of all other bodies is composite and relatively slow； for the reason that each is moving on its own circle with the reverse motion to that of the heavens。 This at once leads us to expect that the body which is nearest to that first simple revolution should take the longest time to complete its circle； and that which is farthest from it the shortest； the others taking a longer time the nearer they are and a shorter time the farther away they are。 For it is the nearest body which is most strongly influenced； and the most remote； by reason of its distance； which is least affected； the influence on the intermediate bodies varying； as the mathematicians show； with their distance。
11
With regard to the shape of each star； the most reasonable view is that they are spherical。 It has been shown that it is not in their nature to move themselves； and； since nature is no wanton or random creator； clearly she will have given things which possess no movement a shape particularly unadapted to movement。 Such a shape is the sphere； since it possesses no instrument of movement。 Clearly then their mass will have the form of a sphere。 Again； what holds of one holds of all； and the evidence of our eyes shows us that the moon is spherical。 For how else should the moon as it waxes and wanes show for the most part a crescent…shaped or gibbous figure； and only at one moment a half…moon？ And astronomical arguments give further confirmation； for no other hypothesis accounts for the crescent shape of the sun's eclipses。 One； then； of the heavenly bodies being spherical； clearly the rest will be spherical also。
12
There are two difficulties； which may very reasonably here be raised； of which we must now attempt to state the probable solution： for we regard the zeal of one whose thirst after philosophy leads him to accept even slight indications where it is very difficult to see one's way； as a proof rather of modesty than of overconfidence。 Of many such problems one of the strangest is the problem why we find the greatest number of movements in the intermediate bodies； and not； rather； in each successive body a variety of movement proportionate to its distance from the primary motion。 For we should expect； since the primary body shows one motion only； that the body which is nearest to it should move with the fewest movements； say two； and the one next after that with three； or some similar arrangement。 But the opposite is the case。 The movements of the sun and moon are fewer than those of some of the planets。 Yet these planets are farther from the centre and thus nearer to the primary body than they； as observation has itself revealed。 For we have seen the moon； half…full； pass beneath the planet Mars； which vanished on its shadow side and came forth by the bright and shining part。 Similar accounts of other stars are given by the Egyptians and Babylonians； whose observations have been kept for very many years past； and from whom much of our evidence about particular stars is derived。 A second difficulty which may with equal justice be raised is this。 Why is it that the primary motion includes such a multitude of stars that their whole array seems to defy counting； while of the other stars each one is separated off； and in no case do we find two or more attached to the same motion？ On these questions； I say； it is well that we should seek to increase our understanding； though we have but little to go upon； and are placed at so great a distance from the facts in question。 Nevertheless there are certain principles on which if we base our consideration we shall not find this difficulty by any means insoluble。 We may object that we have been thinking of the stars as mere bodies； and as units with a serial order indeed but entirely inanimate； but should rather conceive them as enjoying life and action。 On this view the facts cease to appear surprising。 For it is natural that the best…conditioned of all things should have its good without action； that which is nearest to it should achieve it by little and simple action； and that which is farther removed by a complexity of actions； just as with men's bodies one is in good condition without exercise at all； another after a short walk； while another requires running and wrestling and hard training； and there are yet others who however hard they worked themselves could never secure this good； but only some substitute for it。 To succeed often or in many things is difficult。 For instance； to throw ten thousand Coan throws with the dice would be impossible； but to throw one or two is comparatively easy。 In action； again； when A has to be done to get B； B to get C； and C to get D； one step or two present little difficulty； but as the series extends the difficulty grows。 We must； then； think of the action of the lower stars as similar to that of animals and plants。 For on our earth it is man that has the greatest variety of actions…for there are many goods that man can secure； hence his actions are various and directed to ends beyond them…while the perfectly conditioned has no need of action； since it is itself the end； and action always requires two terms； end and means。 The lower animals have less variety of action than man； and plants perhaps have little action and of one kind only。 For either they have but one attainable good （as indeed man has）； or；
