GALILEO AND HIS JUDGES. 53 



at issue, or both arose out of the old Aristotelian 

 philosophy ; and in those days a dissertation which 

 neglected points of this kind would have been looked 

 upon probably with contempt, as evading subjects 

 that it ought to have grappled with. The distinction 

 between natural and artificial motion, which occurs 

 repeatedly in the Dialogue, is an instance of an 

 utterly mistaken notion, having its origin in 

 Aristotle, who, great philosopher though he was 

 in other ways, failed in his investigations of physical 

 science, partly from being misled by verbal fallacies.* 



Another point that our author endeavours to 

 establish in the first day's dialogue is that the Moon 

 is not a polished surface, as Simplicio and others 

 thought, but much like our own Earth, with moun- 

 tains and plains and seas this last being a mistake, 

 as subsequent observation has shown. The solar 

 spots are also discussed, and so, incidentally, is 

 the question whether the heavenly bodies are in- 

 habited, the affirmative opinion finding little favour 

 with any one. 



During the second day the great subject is the 

 revolution of the Earth on its axis ; and Salviati urges 

 forcibly the improbability of the motion of the whole 

 celestial sphere round the Earth in twenty-four hours, 

 including such a number of vast bodies, and with 

 such an immense velocity, while one single body 



* A brief but interesting resume of the Aristotelian physics is 

 given in Whewell's "History of the Inductive Sciences," a work to 

 which I shall have occasion to refer more than once. 



