ii THE EARTH: ITS MOVEMENTS 211 



vary." l No star ever repeats one day the revolution 

 of the previous, or any one year that of another. 

 Mathematical exactness, as we have seen, is never 

 found in the material world : the earth may not always 

 present the same face to the sun, so that one pole must 

 at length pass into the place of the other a change 

 which must occur sensibly and continuously, and 

 irregularly, as natural bodies and elements of bodies 

 are naturally in continuous alteration and movement. 

 " The same composite body is never in exactly the 

 same state at any two moments, nor consists of quite 

 the same parts, for from all sides and everywhere there 

 is, necessarily, an unceasing influx and efflux of 

 elementary bodies." 2 The stars and planets are 

 compared to a flock of birds, which float hither 

 and thither in the clear ether, guided only by their 

 desires. 3 Never does the flock present precisely the 

 same appearance twice. In nature the law is vicissitude 

 and succession, so that each thing may in actual fact 

 come to be all things. 4 



All the stars consist of the same elements, since Earths and 

 water cannot subsist without earth, nor fire without s 

 water ; but in some stars the aqueous element pre- 

 dominates (planets), in others the igneous (suns). 

 From sameness of appearance and of effects (accidents) 

 we may infer sameness of substance. It is clear 

 therefore to Bruno that moon, planets, stars, are all 

 of precisely the same substance as the earth. It is 

 unnecessary to point out by how long a period this 



1 Op. Lot. i. I. p. 360. 2 P. 362, cf. supra. 



s P. 369 (ch. 7)- 



" Promptius utque magis quavis pernice volucrum 

 Versum quaque meent, immensumque aera findant 

 Intima nempe animae vis concitat ilia," etc. 

 4 P. 372. 



