44 



2. How do the two eyes compound the rays of light ? 

 so as to see right ? 



3. Why do we not see all things double ? 



4. Since all things are painted upside down on the 

 bottom of the eye, why do we not see them so ? 



28. We now proceed to the ear, formed withexqui- 

 slte wisdom, for the reception of sounds. The outward 

 ear consisting of an oval cartilage, externally convex, 

 concave within, leads by various windings to the mea- 

 tus auditorius, which is first cartilaginous, and then 

 bony. It is filled with a viscid matter, called the ear- 

 wax, which is supplied from the vessels placed in the 

 skin, surrounding the meatus,- to hinder any hurtful 

 animal from creeping into the ear. The mcatus is clos- 

 ed within by a thin, dry, transparent membrane, affixed 

 to a bony circle, which is called the membrana tym- 

 pani. Behind it is that cavity of the os petrosum, 

 "which is termed the drum. 



The outward ear has two parts, that which stands 

 out from the head, called the auricle, and the narrow- 

 passage which enters the skull, called meatus auditorius. 



The auricle is furrowed with divers winding canals, 

 which receive and collect the various undulations of 

 the air. They who have lost this, hear very confus- 

 edly, unless they use a trumpet, or form a cavity 

 round the hear, with their hands. 



It is a wise provision that the substance of the aLv 

 ricle is cartilaginous. Had it been bone, it would 

 have been troublesome, and might by many accidents 

 have been broken off. If flesh, it would neither have 

 remained expanded, nor so well have received or 

 conveyed the sounds. Rather it would have blunted 

 them, and retarded their progress into the organ. But 

 tyeing hard, and curiously smooth and winding, sounds 

 find an easy passage with a regular refraction, as in a 

 well-built arch, 



It is observable that in infants in the womb, and 

 newly-born, the meatus auditorius is close shut np, 

 partly by the construction of *the passage, and partly 



