SIGHT AND SEEING IN ANCIENT TIMES 427 



might have added with equal truth that when a man appears in a world 

 wholly unprepared to comprehend him, not only are his thoughts 

 neglected, hut his discoveries forgotten. The story that Archimedes set 

 the ships of the Komans on fire by means of burning-glasses is not 

 found in any author who lived near his time. Moreover, the captains 

 of the vessels would hardly be so obliging as to hold their vessels station- 

 ary in order that the old philosopher might work his will on them. 

 Yet the marvelous feats he accomplished on the same occasion and 

 vouched for by credible witnesses are scarcely less incredible. It may 

 be accepted as certain that Archimedes produced wonderful effects 

 by means of his lenses, whether they were made of glass or of some 

 other material. That the ancients as late as the age of Plutarch knew 

 nothing of spectacles is clear from the negative testimony of this writer, 

 whose works might be superscribed ' Concerning all Things and Some 

 Others.' In one of his table talks he tries to explain why old people, 

 when reading, hold the book at some distance from the eyes. He finds 

 the reason to lie in Plato's theory of vision, which he also holds. This 

 philosopher maintained, in common with almost all the thinkers of 

 antiquity, that sight is produced by a sort of fluid substance passing 

 from the visible object to the eye, somewhat in the shape of a cone, the 

 eye being the apex. When the organ becomes weakened by age this 

 attenuated substance is too intense to permit normal vision ; so in order 

 to weaken it the object must be held farther away. He finds a con- 

 firmation of this theory in the habits of those animals that seek their 

 prey by night when their sight is most acute. The fluid emanating 

 from the object is too strong to be properly commingled with the power 

 of vision, as he expresses it, possessed by these animals, but is so weak- 

 ened and diluted by the surrounding darkness as to enable them to see 

 at their best. This may seem to us very puerile ; it ceases to be so when 

 we remember that to this day no one has been able to answer the ques- 

 tion. How do we see? 



Though the art of making glass of certain kinds is very old, 

 spectacles had to wait on the discovery or invention of some method 

 that would produce it perfectly transparent. Specimens of glass have 

 been found in the Egyptian tombs that are more than four thousand 

 years old, and glass bottles are represented on tombs at least fifteen 

 hundred years earlier. In Mesopotamia the art of making glass has 

 been traced for at least two thousand years B. C. But all the glass of 

 antiquity was of inferior quality and was almost useless for purposes 

 where the rays of light were to be transmitted unbroken and with 

 undiminished energy. Mirrors were also made in Egypt thousands of 

 years before the christian era. The materials used were obsidian, 

 metal, zinc and silver. Glass mirrors are mentioned by Pliny, but as 

 they were neither perfectly plane nor foliated they gave back a very 

 imperfect image and were not much esteemed. The word translated 



