vi SIZE AND SHAPE OF BOW 29 



receives its shape also from him. In short, you and 

 I are agreed that those colours by which its quarter 

 of the heaven is adorned proceed from the sun. 

 But on one point we are not agreed : you say that 

 the colour is real ; I maintain that it is only 

 apparent. Whichever it is, real or apparent, it 

 comes from the sun. On your assumption its 

 sudden cessation cannot be explained, seeing that 

 all other bright lights in the sky are dispelled 

 gradually. Its sudden appearance and, at the same 4 

 time, its sudden extinction make for my contention. 

 For it is a peculiarity of a mirror that the reflection 

 in it is not built up piecemeal, but all at once comes 

 fully into being. Every image in it is destroyed, 

 too, with as great rapidity as it was formed. For to 

 the construction or removal of the images nothing 

 is required but the presentation and withdrawal of 

 the objects. 



In the rainbow-cloud whose nature is in ques- 

 tion, there is no proper substance or material : 

 there is only a sham and a likeness without 

 reality. Will you be convinced that this is so? 5 

 The proof is, the rainbow will cease if you conceal 

 the sun. Place another cloud, I repeat, in front of 

 the sun, and ^ all the bright hues of the bow are 

 gone. But what is to be said, you may ask, 



in explanation of the size of the bow which is con- 

 siderably greater than that of the sun ? I have 

 already said that there are certain mirrors that 

 multiply every object they reflect. I may now add 

 that every object much exceeds its natural size when 

 seen through water. Letters, however small and 

 dim, are comparatively large and distinct when 

 seen through a glass globe filled with water. 

 Apples floating in a glass vessel seem more beauti- 



