CHAP, in.! TlIK MICROSCOPE. 233 



CHAPTEK III. 



THE MICROSCOPE. 



THE microscope is an instrument intended to aid the sight by more or 

 less magnifying small objects. This is accomplished by so utilizing 

 the. principles of optics that the objects are as well seen as if it were 

 possible to observe them very much nearer the eye than at the 

 distance of distinct vision. 



There are two kinds of microscopes : the magnifying glass, or simple 

 microscope, and the compound one. 



It is very probable, if not absolutely proved, that the ancients un- 

 derstood the magnifying power of glasses of a spherical form. A passage 

 from one of the comedies of Aristophanes proves that the Athenians 

 understood the way to light a fire by using a piece of glass which con- 

 centrated the sun's rays. The cylinders and stones, so finely engraved, 

 which are left to us by the Assyrians and Eomans, could not have 

 been worked without the assistance of magnifying glasses. Whether 

 these instruments consisted of pieces of glass cut or melted in the 

 form of lenses, or simply hollow glass balls filled with w^ater, is 

 uncertain ; but the latter supposition is renctered probable by the 

 following passage from Seneca : " All objects seen through water," 

 he says, " appear larger. Faint and indistinct characters, read through 

 a glass ball filled with water, are larger and clearer to the eye." But 

 if the ancients were aware of the optical power of spheres of water, 

 or glass, or even of glass lenses, it does not seem that they possessed 

 any precise method of using or of making them. They have left no 

 observation in natural history which would confirm the scientific use 

 of the magnifying glass in ancient times. 



