32 CELESTIAL, ATMOSPHEEIC, AND 



That the Moon is spherical is shown, he says, by her phases 

 and by solar eclipses.* He says also that the Earth is 

 spherical, this being shown by eclipses of the Moon, and 

 that geometers had calculated the circumference of the Earth 

 to be about forty-six thousand miles, t Other philoso- 

 phers, before Aristotle's time, believed that the Earth was 

 spherical, e.g., the Pythagoreans, according to Zeller.t In 

 opposition to the Pythagoreans and others, he held that 

 the Earth was the centre of the Kosmos, and this conclusion 

 was based on his assumptions about the nature of the 

 elements and their proper motions, for, according to these 

 assumptions, motion about a centre, whether a motion of 

 rotation or revolution, would not be natural to the Earth or 

 any part of it. He decided that the Earth was at rest at 

 the centre of the Kosmos, and must necessarily tend to 

 that position for several reasons, one being that heavy 

 bodies thrown upwards, even to a great height, fall directly 

 downwards to the places whence they are thrown, § for he 

 considered that the Earth would act like any of its parts. 

 Aristotle's belief, previously referred to, that, passing out- 

 wards from the centre, earth, water, air, and fire are arranged 

 above one another in the order named, seems to be a develop- 

 ment of Anaximander's belief that the earth, the air, and an 

 envelope of fire, enclosing the whole, were produced by 

 successive processes of separation from his fluid primitive 

 matter. 



Before proceeding further with Aristotle's views on the 

 Earth and terrestrial phenomena, some of his statements 

 about certain celestial and atmospheric phenomena, such 

 as falling stars, the Milky Way, and rainbows, will be 

 considered. 



These phenomena, according to Aristotle, have a less 

 orderly arrangement than the stars and planets, il The 

 explanations he gives to account for the formation of falling 

 stars, comets, the Milky Way, and various other kinds of 

 luminous and moving appearances in the sky are somewhat 

 alike. He bases most of his explanations on an assumed 

 ascent of exhalations from the Earth, parts of such exhala- 

 tions being afterwards ignited in consequence of the motions 

 of the upper regions of the Kosmos. The exhalations were 

 supposed to be of two kinds : (1) an essentially watery vapour, 



- De Coelo, ii. c. 11. f De Coelo, ii. c. 14, 2976 and 298a. 



X History of Greek Philosophy, translated by S. F. Alleyne, 1881, 

 vol. i. p. 454. § De Coelo, ii. c. 14, 2966. || Meteorol. i. c. 1, s. 2. 



