TEREESTEIAL PHENOMENA. 37 



rainbows discovered long after his time by Theodorich and 

 De Dominis on the refractions by the raindrops and reflec- 

 tions at their surfaces, by Descartes on the concentration of 

 the rays of hght in particular directions, and by Newton on 

 the differences of refrangibility of different coloured rays, 

 Aristotle's explanations are cumbersome and often fanciful. 

 It is not easy to understand his meaning, and there are 

 indications in his description that he found the explanations 

 very difficult. He makes several assumptions, most of them 

 faulty, and it is not always clear on which of these assump- 

 tions he relies when attempting to explain certain details of 

 the phenomena. The following is an epitome of Aristotle's 

 views, from which the peculiarities of his explanations, 

 referred to above, will be evident. It will also be noticed 

 that he speaks of the rays of light being reflected towards 

 the object seen. Visual rays, he says, are reflected from all 

 smooth surfaces, such as those of water and air, and such 

 reflection takes place from compressed air and also from air 

 which is not compressed, if the visual rays are weak, just as 

 happened in the case of one man whose sight was weak, for 

 he always saw an image of himself in front of him, as 

 he walked.* The reflection is stronger from water and 

 especially from vapour which is just being condensed into 

 water, for then each of its parts acts like a mirror, t On 

 account of the extreme smallness of such mirrors, however, 

 colour only and not form will be seen, but the succession of 

 mirrors similarly situated will give a continuous band of 

 similar colour. The same reasoning applies to all the 

 mirrors, and so a rainbow is formed. I 



Again, a rainbow is caused by the reflection of visual 

 rays by a cloud to the Sun, the cloud being dark and the 

 visual rays having to extend through a long distance. A 

 bright object, however, shining through anything dark or in 

 anything dark — for, he adds, it makes no difference which it 

 is — is red. In order to exemplify this, he remarks that the 

 Sun appears to be red when seen through mist or smoke, 

 and that the flame of a fire of green wood appears to be of 

 a red colour, by reason of its being seen mingled with a 

 large amount of smoke. § He says that this explains why 

 one of the colours of the rainbow is red.|| Continuing his 



* Meteorol. iii. c. 4, ss. 2 and 3. f Ibid. iii. c. 4, s. 5. 



I Ibid. iii. c. 4, bs. 6 and 7. ^5 Ibid. iii. c. 4, ss. 9-11. 



II Ibid. iii. c. 4, s. 12. 



