ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 581 



at objects at a distance. This interpretation of the passage of Pliny is 

 confirmed by the words of the preceding paragraph (ib., 53) : " oculi . . . 

 in homine . . . promiuentes, quos hebetiores putaut, etc. ; " but promi- 

 nent eyes are almost always short-sighted eyes, and therefore the 

 epithet Jiehetiores corresponded to short-sighted ones ; and Nero's eyes 

 having been called hebetes in the passage quoted just before, will have 

 been short-sighted, which is also asserted by Suetonius, (22) who says 

 (" oculis csesiis et hebetioribus " j, with sea-green or pale-blue eyes, 

 and very weak, that is, only good for seeing very near objects, or in 

 other words, with the eyes of a myope. 



And that the epithet hehes (blunt, obtuse, inefficient, weak, &c.) 

 applied to the eye did with the ancients correspond to our word 

 myope we have another proof in this, that up to the beginning of the 

 seventeenth century they continued to call weak sights, and spectacles 

 for weak sights, the eyes and spectacles of the short-sighted. (23) 



That other passage of Pliny also clearly makes allusion to Nero's 

 short sight (Ixxsvii. 16), which has made many believe that the ancients 

 were acquainted with concave lenses, and used them to lengthen the 

 sight of short-sighted people. This passage of the celebrated naturalist 

 says that these emeralds " quorum . . . corpus extensum est (eadem, 

 qua specula, ratione), supini imagines rerum reddunt. Nero princeps 

 gladiatorum pugnas spectabat smaragdo." " These emeralds, which are 

 sufficiently large (acting like looking-glasses) placed with the re- 

 flecting face upwards, give the images of things. The Emperor Nero 

 watched the fights of the gladiators with an emerald." 



Now, speaking in this passage exclusively of emeralds large enough 

 to be used as mirrors, one cannot understand how with some learned 

 men these mirrors in passing through Nero's hands can have become 

 lenses. Pliny speaking therefore in this place not of a lens but of an 

 emerald mirror, every one will easily understand that a mirror would 

 have been useless to Nero, if he were long-sighted ; for neither a plane 

 nor a convex nor a concave mirror would have been of any use to a 

 long- sighted person to look at things a long way off, for a long-sighted 

 man sees far without any aid whatever. 



On the other hand, if Nero was short-sighted, an emerald with its 

 top surface worked spherically with its face uppermost, as Pliny says in 

 front of and below the two eyes, or it might be below the one, could 

 have perfectly fulfilled the office of a concave lens, and present the 

 short-sighted emperor at a few centimetres from his eyes the images of 

 the amjihitheatre, and of its distant gladiators, and enable him thus to 

 see them distinctly. The same eifect might have been produced by an 

 emerald, plane on the side turned towards the eyes and the objects to be 

 viewed, and spherically concave beneath, as according to Pliny many 

 were then made (xxxvii. 16) : " lidem (emeralds) plerumque et concavi ut 

 visum colligant." " One often finds some (emeralds) concave to collect 

 sight," that is, it shows many things in a small field, for in that case the 

 reflection takes place on the convex surface of the scooped-out face, and 

 the light in passing from the emerald to the air must have been strono-, 

 and given rise to virtual images very clear and close to the eyes of 

 the observer. (24) 



One must not think emeralds large enough to serve as looking- 

 glasses with convex surfaces especially rare, as there are emeralds ten 

 centimetres long and five wide, others five long and three wide, (25) not 



