TERRESTRIAL PHENOMENA. 35 



differ in the design (rojxix/a) of their colours,* but he does not 

 explain in what way they differ, so that it cannot be said 

 that he was aware of the difference between the arrangements 

 of the colours, previously referred to, of a primary rainbow 

 and a coloured halo. In Meteorol. iii. c. 3, ss. 10 and 11, 

 when dealing with the colours of solar halos, he says that 

 the mirrors, although severally invisible on account of their 

 smallness, are contiguous and form one ring in which the 

 Sun is reflected so that a whiteness of the halo is evident. 

 He states correctly that halos are less frequently seen about 

 the Sun than about the Moon.t 



Aristotle refers, in several passages, to parhelia or mock 

 suns, but some of his statements about them are incorrect. 

 Like halos, in association with which they are sometimes 

 seen, parhelia are caused by refraction of sunlight shining 

 through a cirrus or like cloud containing minute ice crystals. 

 The parhelia usually occur to the right and left of the Sun, 

 at a distance of about 22° therefrom. Aristotle says that 

 parhelia are due to reflection of the visual rays from some- 

 thing to the Sun,t and, it seems, from Meteorol. iii. c. 6, s. 5, 

 that this something is a dense mist or cloud, the watery 

 vapour of which is in the act of condensing into raindrops 

 and so uniformly constituted as to form, in effect, an even 

 mirror reflecting an image of and of the same colour as the 

 Sun, the reflection being compared with that which takes 

 place at the surface of polished bronze. 



He was aware that the appearance of a parhelion was 

 an indication of unsettled weather. § Parhelia are produced, 

 according to Aristotle, to the right and left of the Sun, and 

 neither above it nor below it, and he adds correctly that 

 they are not formed very close to the Sun nor very far 

 away. 11 



The appearance and mode of formation of certain streaks 

 of coloured light, which Aristotle calls "rods" {pci/3^oi), are 

 described by him, but his descriptions are difficult to under- 

 stand. The streaks of light are probably those which are 

 seen among clouds at sunrise and sunset, producing the 

 magnificent colour effects, which are so well known. 



Aristotle says that the " rods " usually appear about 

 sunrise and sunset, and always to the right or left of the 



* Meteorol. iii. c. 4, s. 9. -j- Ibid. iii. c. 3, s. 1*2. 



I Ibid. iii. c. 6, s. 1. § Ibid. iii. c. 6, s. 6. 



II Ibid. iii. c. 2, s. 6, iii. c. 6, s. 7. 



