A HISTORY OF SCIENCE 



again begin to move. The other stars in the mean 

 while, which unquestionably move, all have, as was 

 said, a great circle for an orbit and keep this un- 

 changeably. 



"The improbability is further increased this may 

 be considered the sixth inconvenience by the fact 

 that it is impossible to conceive what degree of solidity 

 those immense spheres must have, in the depths of 

 which so many stars are fixed so enduringly that they 

 are kept revolving evenly in spite of such difference of 

 motion without changing their respective positions. 

 Or if, according to the much more probable theory, the 

 heavens are fluid, and every star describes an orbit of 

 its own, according to what law then, or for what reason, 

 are their orbits so arranged that, when looked at from 

 the earth, they appear to be contained in one single 

 sphere? To attain this it seems to me much easier 

 and more convenient to make them motionless in- 

 stead of moving, just as the paving - stones on the 

 market-place, for instance, remain in order more easily 

 than the swarms of children running about on them. 



"Finally, the seventh difficulty: If we attribute the 

 daily rotation to the higher region of the heavens, we 

 should have to endow it with force and power sufficient 

 to carry with it the innumerable host of the fixed stars 

 every one a body of very great compass and much 

 larger than the earth and all the planets, although 

 the latter, like the earth, move naturally in an opposite 

 direction. In the midst of all this the little earth, 

 single and alone, would obstinately and wilfully with- 

 stand such force a supposition which, it appears to 

 me, has much against it. I could also not explain why 



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