94 



the small pupil! that the rajs of light should paint on 

 the optic nerre, puint in an instant of time, paint in 

 their truest colours and exactest lineaments, every 

 species of external object ! 



The eye is so tender, that the slightest touch might 

 injure its delicate frame. It is guarded, therefore, 

 with peculiar care, intrenched deep, and barricaded 

 round with bones. As the smallest fly might incom- 

 mode its polished surface, it is farther protected by 

 two substantial curtains In sleep, when there is no 

 occasion tor the sense, but a necessity to guard the 

 organ, these curtains close of their own accord. At 

 any time they fly together as quick as thought. They 

 are lined with an extremely fine sponge, moist with its 

 own dew. Its bristly palisades keep out the least 

 mote, and moderate ihe too strong impressions of the 

 light. 



As in oTir waking hours we have almost incessant 

 need for these little orbs, they run upon the finest 

 castors, rolling every way with the utmost ease ; which 

 circumstance, added to the flexibility of the neck, ren- 

 ders our two eyes as useful as a thousand. 



The Isar -consists of an outward porch and inner 

 rooms. The 'porch somewhat prominent from the 

 head, is of a cartilaginous substance, covered with 

 tight membranes, and wrought into sinuous cavities. 

 These, like circling hills, collect the wandering undu- 

 lations ot the air, and transmit them vtith a vigorous 

 impulse to the 'finely stretched membrane of the drum. 

 This is expanded upon a circle of bones, over a po- 

 lished reverberating cavity. It is furnished with braces 

 that strain or relax, as the sound is faint or strong. 

 The hammer and the anvil, the winding labyrinth, 

 and the sounding galleries, these and other pieces of 

 mechanism, all instrumental to hearing, are inexpres- 

 sibly curious. 



Amazingly exact must be the tension of Ihe auditory 

 nerves, since they answer the smallest tremors of the 

 atmosphere, and distinguish their most subtle varia. 



