164 ASTRONOMICAL HISTORY. 



seem to be a union of the denser in the centre, and an ex 

 pulsion of the rarer substances, to the circumference. Now 

 it contributes materially to science to know the connexions 

 of questions with one another, because under some of them 

 there is found history or inductive matter to furnish their 

 solution, under others none. 



But granting a system, next comes our second question, 

 What is the centre of the system ? For if to any of the 

 orbs ought to be assigned the central place, there appear 

 first to be two orbs which present the character of a middle 

 point or centre the earth and the sun. In favour of the 

 earth there are our senses, and immemorial opinion, and 

 most of all this circumstance, that as dense bodies contract 

 into a narrow, and rare are diffused over a wide space, 

 and the area of every circle contracts towards its centre, 

 it seems to follow of necessity that the contracted part 

 should be placed at the centre of the world, as the appro 

 priate, and, as it were, the only place for dense bodies. For 

 the sun again this reason makes, that to a body whose 

 functions in the system are greatest and most potent, that 

 place ought to be assigned from which it can best act 

 upon, and diffuse its influence over the entire system. To 

 this we may add that the sun evidently has as his satellites 

 Venus and Mercury, and, in the opinion of Tycho, also the 

 rest of the planets ; so that the sun plainly appears to pos 

 sess the nature, and to perform, in some instances, the office 

 of a centre. Therefore we are brought so much nearer 

 the determination that it is the centre of the universe, which 

 was the assertion of Copernicus. But in the system of 

 Copernicus there are many and great difficulties : first, there 

 is something revolting to belief, in encumbering the earth 

 with three motions, in detaching the sun from the group of 

 planets with which it has so many common properties, 

 in introducing so much immobility into the system of 

 nature, (particularly by making the stars and sun immove- 

 able, the bodies most luminous and sparkling of any), in 

 wishing to fasten, as it were, the moon to the epicycle 

 of the earth, and in some other assumptions which he 

 makes ; savouring of the character of a man who thinks 

 nothing of inventing any figment at the expense of na 

 ture, provided the bowls of haphazard roll well. But if 

 we are to ascribe motion to the earth, it seems more consis 

 tent to banish the idea of a system, and of various globes 

 conceived to be distributed over space, according to the idea 

 of those whom we have already mentioned, than to estab- 



