chap, xxviii.] SIMPLE MICROSCOPE 357 



be the divergence between their backward pro- 

 longations, and consequently the more magnified the 

 image. The single biconvex lens, then, forms a simple 

 microscope for viewing very small objects. The 

 property of a biconvex lens was evidently known to 

 the ancients, at least to the Greeks and Romans. 

 " There is in the French cabinet of medals a seal, 

 said to have belonged to Michael Angelo, the fabri- 

 cation of which, it is believed, belongs to a very 

 remote epoch, and upon which fifteen figures have 

 been engraven in a circular space of fourteen milli- 

 metres in diameter. These figures are not all visible 

 to the naked eye" At the Belfast meeting of the 

 British Association in 1852, Sir David Brewster 

 showed a lens, made out of rock crystal, which had 

 been found among the ruins of Nineveh, and which 

 he believed to have been used for optical purposes. 

 The magnifying power of globes filled with water was 

 also known at an early period. Nevertheless, the 

 valuable properties of lenses were not to any extent 

 known till the middle of the seventeenth century. 



The application of these properties to form an in- 

 strument for magnifying small objects, is ascribed to 

 Zacharias Jansen and his son, of Middleborough, in 

 the low countries, who made microscopes in 1590. 

 A Neapolitan, named Francis Fontana, claims to have 

 invented the instrument independently in 1618. A 

 Dutch alchemist, Cornelius Drebbel, brought one of 

 Jansen's instruments to London in 1619, which was 

 seen by William Borrelli and others. Drebbel him- 

 self made microscopes in London in 1621. With the 

 simple microscope much remarkable work was done. 

 It was with such an instrument that Lieberkiihn, 

 Leuwenhoech, and Swammerdam worked. Leuwen- 

 hoech had a separate lens for nearly every object he 

 examined. 



The difficulties, however, in the use of highly 



