Page:A short history of astronomy(1898).djvu/75

§ 29] through the familiar phases of crescent, half full, gibbous, full moon, and gibbous, half full, crescent again.



Aristotle then argues that as one heavenly body is spherical, the others must be so also, and supports this conclusion by another argument, equally inconclusive to us, that a spherical form is appropriate to bodies moving as the heavenly bodies appear to do.



29. His proofs that the earth is spherical are more interesting. After discussing and rejecting various other suggested forms, he points out that an eclipse of the moon is caused by the shadow of the earth cast by the sun, and