34 CELESTIAL, ATMOSPHERIC, AND 



star could produce a comet, as stated previously, then a 

 similar result would be produced beneath the vast number 

 of stars vi^hich are collected together in the Milky Way.* 

 The milky appearance he considered to be due to the tails, 

 apparently coalesced, of the numerous comets or comet-like 

 effects thus produced, t 



Amid all these fanciful explanations, it is quite clear 

 that Aristotle fully appreciated one fact, viz., the existence 

 of numerous stars, many of large size, in the Milky Way. 



He explains the views of other philosophers, viz., the 

 Pythagoreans, who believed that the Milky Way was the 

 path of the planets, Anaxagoras and Democritus, who held 

 that it was the light of certain stars, which, hidden from the 

 Sun by the Earth, shone with a light of their own so as to 

 produce a milky aspect, and some philosophers who con- 

 sidered the Milky Way to be caused by reflection. This, 

 he says, was nearly all that had been said by others on this 

 subject.! 



Rainbows and what he calls halos, parhelia, and rods or 

 streaks of light are, Aristotle says, all caused by anaklasis.% 

 Anaklasis means a bending or breaking aside, and, as used 

 by Aristotle in his statements about light, a reflection. 



It is not clear that all Aristotle's statements about halos 

 relate to the phenomena now called by that name, but most 

 of them seem to do so. Halos, white and coloured, have 

 been seen about the Sun, the Moon, and the planet Venus, 

 when these celestial bodies were shining through cirrus or 

 like clouds. These clouds are now believed to contain vast 

 numbers of ice crystals, which act like prisms. Those 

 crystals which send the maximum amount of light to the 

 eye of the observer form a circular ring, and the effect of 

 refraction by these is to produce, in the case of a coloured 

 halo, a circular spectrum-band with the red on the inner 

 side and not on the outer, as in a primary rainbow. 



Aristotle's explanation of the way in which a halo is 

 produced has a superficial resemblance to the above, but he 

 considers that it is formed when the light of the Sun, the 

 Moon, or a bright star or planet, shines through a uniformly 

 moist cloud and is reflected by a circular ring of watery 

 particles which form part of the cloud, and act like so many 

 small mirrors. II He says that the rainbow and the halo 



* Meteorol. i. c. 8, bs. 11 to 13. f Ibid. i. c. 8, s. 20. 



I Ibid. i. c. 8, ss. 4 and 10. § Ibid. iii. c. 2, s. 7. 



II Ibid. iii. c. 2, s. 2, c. 3, ss. 2, and 7 to 9. 



