36 THE MICROSCOPE. 



errors of vision arising therefrom. The first actual mention of facts 

 known concerning refraction and reflection however is by Ptolemy 

 in about the middle of the second century A. D. 



In Knight's Mechanical Dictionary we find (without dates or 

 authorities) that the magnifying power of glass balls was known in 

 the very early time to the Chinese, Japanese, As.syrians and 

 Egyptians and more recently to the Greeks and Romans. He 

 states too that lenses for microscopical purposes long preceded their 

 application to telescopes. 



As further evidence of the knowledge of the ancients concern- 

 ing the burning and magnifying power of lenses, Priestley thinks 

 (Optics p. 8) it is hardly possible for those frequently handling the 

 gems fashioned in spheres or as lentils, now seen in cabinets, could 

 possibly have escaped noticing their magnifying or burning power. 

 Some of them are supposed to be traceable to the Druids. One of 

 spherical form of about one and one-half inches in diameter can be 

 seen among the fossils given to the University of Cambridge by Dr. 

 Woodward. 



On theoretical optics, Aristotle, B. C. fourth century, wrote 

 largely. Archimedes as before stated also wrote. But from 

 Euclid's time to that of Seneca', who lived about 65 A. D., there 

 appears nothing on this subject. Seneca gave us nothing new, but 

 redresses the crude sentiments advanced years before by Aristotle. 

 The first important advance made in this science was by Ptolemy at 

 time before mentioned. 



After Ptolemy came a dark age in Europe, during which time 

 the sciences were cultivated by the Arabs chiefly. The first writer 

 according to Priestley (p. 19) was Al. Farabi, who lived 900 A. D., 

 but of his works we can find no trace. In the year 1000 A. D., 

 Ebu Haithem wrote largely on this subject, but his work is also 

 lost. The only work left us from the Arabian philosophers was by 

 Alhazen's pen, who flourished during the 12th century. It is in this 

 work that we find a distinct account of the magnifying power of 

 glasses, and it is supposed by some that what he wrote on the sub- 

 ject was the incentive to the invention of spectacles. He describes 

 the effect on objects when placed close to the base of a larger seg- 



I Quest. Nat. 



