110 DISCOURSE ON THE STUDY 



systematic, without knowing what to say. Thus 

 he divides motions into natural and unnatural ; the 

 natural motion of fire and light bodies being up- 

 wards, those of heavy downwards, each seeking its 

 kindred nature in the heavens and the earth. Thus, 

 too, the immediate impressions made on us by ex- 

 ternal objects, such as hardness, colour, heat, &c. 

 are referred at once, in the Aristotelian philosophy, 

 to occult qualities, in virtue of which they are as 

 they are, and beyond which it is useless to enquire.* 

 * Galileo exposes unsparingly the Aristotelian style of rea- 

 soning. The reader may take the following from him as a spe- 

 cimen of its quality. The object is to prove the immutability 

 and incorruptibility of the heavens ; and thus it is done : 



I. Mutation is either generation or corruption. 

 II. Generation and corruption only happen between con- 

 traries. 



III. The motions of contraries are contrary. 



IV. The celestial motions are circular. 

 V. Circular motions have no contraries. 



o. Because there can be but three simple motions. 



1. To a centre. 



2. Round a centre. 



3. From a centre. 



/3. Of three things, one only can be contrary to one. 



7. But a motion to a centre is manifestly the contrary 



to a motion from a centre. 



8. Therefore a motion round a centre (i, e* a circular 



motion) remains without a contrary. 



VI. Therefore celestial motions have no contraries there- 

 fore among celestial things there are no contraries 

 therefore the heavens are eternal, immutable, in- 

 corruptible, and so forth. 



It is evident that all this string of nonsense depends on the 

 excessive vagueness of the notions of generation, corruption, 

 contrariety, &c. on which the changes are rung. See GALI- 

 LEO, Sy$lema Cosmicum, Dial. i. p. 30. 



