20 PHYSICAL SCIENCE BK. i 



10 see none at all- ? Besides, as there is but one colour 

 in the sun, why are there different colours in the 

 reflections of him ? These objections which you 

 have put forward, as well as others that no less call 

 for refutation, I will endeavour to refute. And let 

 me say, first of all, that nothing is more deceptive 

 than our eyesight, not merely in objects whose 

 careful examination is prevented by distance in 

 position, 1 but even in objects seen close at hand. 

 An oar, though quite whole, presents the appear- 

 ance of being broken when seen in clear shallow 

 water. Apples seen through glass appear much 



11 larger than they really are. In long colonnades, 

 pillars set at intervals present an apparently un- 

 broken continuity of line. Or go back to the case 

 of the sun himself; his orb, which reason proves 

 to be larger than the whole earth, is so contracted 

 by human sight that some of the philosophers have 

 maintained that it is only a foot in diameter. He 

 is, we know, the swiftest of all luminaries, yet none 

 of us can see him move ; nor should we believe 

 that he does advance, were it not evident from time 

 to time that he has advanced. The world itself 

 glides on with headlong speed ; within an instant of 

 time it unfolds its risings and its settings, yet none 



12 of us is aware of its movement. What cause, then, 

 is there for wonder if our eyesight cannot separate 

 the drops of the rain showers, and loses the dis- 

 tinction of the images on account of the vast 

 distance at which they are beheld ? At any rate 

 no one can doubt this, that the rainbow is a 

 reflection of the sun, formed in a hollow cloud full 

 of moisture. This is made plain from the simple fact 

 that the image is never seen except opposite the sun, 



1 The received text gives "diversity of colours." 



