GALILEO AND HIS JUDGES. 141 



than that of the Earth, which Venus obeyed ; the 

 same was true of Mercury, with the difference that 

 this planet was much nearer to the Sun. Then 

 as regards the superior planets, Mars, Jupiter, Saturn, 

 the probability that the Sun was the great central 

 power that controlled their movements was a very 

 strong one. There is but little to add on these 

 topics to Galileo's own forcible argument in the 

 third day's dialogue ; he is, however, inaccurate in 

 his figures, and states that Mars appears sixty times 

 as large when in opposition to the Sun, as at con- 

 junction. More recent observations have shown that 

 he appears rather more than thirty times as large 

 when at his nearest point to the Earth, than he 

 does when near his conjunction with the Sun, and 

 consequently at his farthest point from the Earth ; 

 but this variation is quite sufficient for the argument, 

 and proves incontestably that if Mars revolves round 

 the Earth as in any way the centre of his orbit, it 

 must be in an ellipse of so great eccentricity as 

 no one could reasonably imagine him to do ; indeed, 

 the anti-Copernicans of Galileo's day knew nothing 

 of the elliptic motions of the planets ; neither, as 

 we have seen, did Galileo himself. 



The same argument, drawn from the apparent 

 size of the planet at different periods, applies also 

 to Jupiter and SaturD the other exterior planets 

 were discovered much later only not so strikingly 

 as in the case of Mars. The improbability, if we 

 once admit that all the planets revolve round the 



