PHENOMENA OF LIGHT AND COLOUR. 65 



the eye and an object of vision. The inversion of headlands 

 in the sea, to which he refers, is probably nothing but that 

 produced by reflection at the surface of the water, and is 

 intended to show how untrustworthy the sight may be, just 

 as in the case of the man who, Aristotle says, saw his own 

 image reflected by the air in front of him. 



The observation, that all things seem to be larger when 

 easterly winds blow, may refer to the apparent nearness 

 which is associated with moist atmospheres. According to 

 Aristotle, the easterly winds referred to were hot and, at 

 first, dry, but became moist. I have made enquiries, but 

 have been unable to ascertain whether such a phenomenon 

 occurs at Athens, when easterly winds blow. 



Aristotle s reference to the apparent magnification of 

 the sun and stars is correct, but here again the effect is not 

 due to refraction. It is now known that there is no mag 

 nification, the result being mainly psychological. Seneca 

 attempts to explain the apparent magnification of the sun 

 and stars by saying that our sight is not reliable in the case 

 of an object seen in water or through a moist medium, for, 

 if a ring is thrown into a bowl filled with water, yet, 

 although the ring lies at the very bottom of the bowl, its 

 image is seen near the top of the water. Whatever, he 

 says, is seen through a liquid or moist medium appears to 

 be far larger than it really is.* It is evident that Seneca, 

 who was well acquainted with Aristotle s works, did not 

 understand the phenomena of refraction. He developed 

 Aristotle s idea that the apparent magnification was due to 

 weak sight, or sight under unusual conditions, the nature of 

 which Aristotle himself does not explain. 



The knowledge of the Ancients about refraction was of 

 very slow growth. Some of them made observations on 

 this subject, for Archimedes is said to have written a book 

 on the appearance of a ring seen in water, and Seneca refers 

 to the broken appearance of an oar dipped in water,! the 

 magnification of letters seen through a glass globe filled 

 with water, and the fairer appearance of apples seen floating 

 in water in a glass vessel.! Neglecting the work on Optics, 

 probably wrongly assigned to Ptolemy, containing many 

 interesting observations on the refraction of light by glass, 

 water, and air, no important advance was made in the study 



* Nat. Qucest. i. c. 6, ss. 5 and 6. f Ibid. i. c. 3, s. 9. 



I Ibid. i. c. 6, s. 5. 



F 



