in COLOUR OF RAINBOW 21 



high up or low down, in inverse relation, just as he 

 sinks or elevates his course. When he descends, 

 it is higher ; when he is high in the heavens, it is 

 more sunken. A cloud of the required kind is 13 

 often at the side of the sun without producing a 

 rainbow, because it does not catch his image 

 straight in front. 



As to the variegation in colour, it is due 

 simply to its double source, derived partly from 

 the sun, partly from the moist cloud. The mois 

 ture produces lines now blue, now green, now 

 purple-like, and orange or red the two shades, 

 dull and bright, combining to produce this diversity. 

 So also, a purple garment does not always come 14 

 out in exactly the same tint from the same dye. 

 Differences depend upon the length of time it has 

 been steeped, the consistency and the amount of 

 moisture in the dye it has imbibed : it may be 

 dipped and boiled more than once, or it may have re 

 ceived only one immersion. In like manner then, 

 when there are the two elements, sun and cloud, 

 in other words, object and mirror, it is little wonder 

 that as many varieties of colour are generated as can 

 be produced from them in higher or lower tone in 

 countless different categories. For example, there 15 

 is one colour that proceeds from the light of fire, 

 another from a light that is duller and less violent 

 than fire. In other details concerning the rainbow 

 the method of inquiry is full of uncertainty ; there 

 is nothing concrete to lay hold upon, and conjecture 

 must be ventured in every direction. But in this 

 question of its origin doubt is precluded ; for it is 

 evident that the causes of the rainbow are two in 

 number, sun and cloud. The bow never appears 

 when the sky is clear, and never when it is so 



