42 CELESTL\L, ATMOSPHERIC, AND 



conspicuous. Aristotle, however, states that a lunar rainbow 

 seems to be quite white.* 



He also refers incidentally to the formation of rainbows 

 in spray raised by oars from the sea, or in spray scattered 

 by hand away from the sun, but he states incorrectly that, 

 in these cases, the colours are more like those seen about 

 lamps, there being, apparently, not a light red but a purple 

 colour. + 



This represents the main part of Aristotle's descriptions 

 of rainbows. Many of his statements are inaccurate, as has 

 been mentioned already, but yet none of his work on celes- 

 tial, atmospheric, and terrestrial phenomena shows more 

 clearly the use of a careful method of inquiry. Further, 

 his descriptions of the way in which rainbows and their 

 colours are produced serve to illustrate some of the difficult 

 passages on light and colour which will be considered in 

 Chapter iv. 



Unlike some ancient philosophers, Aristotle did not 

 believe that air, when in motion, was wind, while the same 

 air, when condensed, was rain.t He believed that rain 

 originates from an exhalation, essentially vaporous, and 

 wind from another exhalation, essentially dry or smoke-like, 

 both being raised by the heat of the Sun and always asso- 

 ciated together. § He was influenced by observations show- 

 ing that during dry years, when the dry and smoke-like 

 exhalation was most abundant, winds were most frequent, 

 while the vaporous exhalation was most abundant during wet 

 years. II 



Aristotle knew that winds were due to the action of 

 solar heat, but beyond this his views on their production 

 were untrustworthy. The action of solar heat is to rarefy 

 parts of the atmosphere, and the rarefied parts rising 

 upwards are replaced, more or less violently, by colder and 

 heavier air. These processes, so well-known to result in the 

 occurrence of winds, do not seem to have been known to 

 Aristotle. He believed that the dry, smoke-like exhalation 

 was, as he says in various passages, the origin, nature, or 

 substance of winds. Like those of other ancient philo- 

 sophers, his ideas about the composition of the atmosphere 

 were very crude, and it is difficult to understand what he 

 considered the dry, smoke-like exhalation to be, but it is 



* Meteorol. in. c. 4, s. 28. f Ibid. iii. c. 4, ss. 17-19. 



I Ibid. ii. c. 4, s. 7. § Ibid. ii. c. 4. ss. 2-5. 



li Ibid. ii. c. 4. s. 10. 



