2 HISTORY OP THE MICROSCOPE. 



the Greeks and Romans ; at any rate, it is tolerably certain 

 that spectacles were used as early as the thirteenth century. 

 Now as the glasses of these were made of different con- 

 vexities, and consequently of different magnifying powers, 

 it is natural to suppose that smaller and more convex 

 lenses were made, and applied to the examination of 

 minute objects. Many among the learned refuse to the 

 ancients a knowledge of magnifyiug lenses, and a fortiori 

 that of refracting telescopes, since, according to them, the 

 Greeks and Romans had only very imperfect notions with 

 respect to the fabrication of glass. 



From a passage in Aristophanes it is plain that globules 

 of glass were sold at the shops of the grocers of Athens, in 

 the time of that comic author. He speaks of them as 

 " burning spheres." 



Pliny states that the immense theatre (it was capable of 

 containing eighty thousand persons) erected at Rome by 

 Scaurus, son-in-law of Sylla, was three stories in height, 

 and that the second of these stories was entirely inlaid 

 with a mosaic of glass. 



Ptolemy, in his " Optics," has inserted a table of the 

 refractions which light experiences under different angles 

 of incidence, in passing from air into glass. The values 

 of these angles, which differ only in a slight degree from 

 those obtained in the present day by means of similar ex- 

 periments, prove that the glass of the ancients differed 

 very little from that manufactured in our own times. 



There is in the French Cabinet of Medals a seal, said to 

 have belonged to Michael Angelo, the fabrication of which, 

 it is believed, ascends to a very remote epoch, and upon 

 which fifteen figures have been engraven in a circular 

 space of fourteen millimetres in diameter. These figures 

 are not all visible to the naked eye. 



Cicero makes mention of an Iliad of Homer written 

 upon parchment, which was comprised in a nutshell. 



Pliny relates that Myrmecides, a Milesian, executed in 

 ivory a square figure which a fly covered with its wings. 



Unless it be maintained that the powers of vision of our 

 ancestors surpassed those of the most skilful modern 

 artists, these facts establish that the magnifying property 

 of lenses was known to the Creeks* and Romans nearly 



