128 SENSES. 



a wonderful degree of exactness, by the sense of touch ; and 

 the power they frequently possess of determining when they 

 approach a wall, has been attributed in part to their percep- 

 tion of the effects produced upon the skin by the air, either 

 on account of the change in the degree of its resistance, or 

 from some other alteration in it with which we are unac- 

 quainted.' 



Of Seeing. 



Of all the senses, that of seeing is unquestionably the 

 noblest, the most refined, and the most extensive. The ear 

 informs us of the existence of objects at comparatively small 

 distances; and its information is often imperfect and falla- 

 cious. But the organ of sight, which is most admirably con- 

 structed, not only enables us to perceive thousands of objects 

 at one glance, together with their various figures, colors, and 

 apparent positions, but, even when unassisted, to form ideas 

 of the sun and planets, and of many of the fixed stars; and 

 thus connects us with bodies so remote, that imagination is 

 lost when it attempts to form a conception of their immense 

 magnitude and distances. This natural field of vision, how- 

 ever great, has been vastly extended by the invention of 

 optical instruments. When aided by the telescope, the eye 

 penetrates into regions of space, and perceives stars innumer- 

 able, which, without the assistance of art, would to us have 

 no existence. Our ideas of the beauty, magnitude, and re- 

 moteness or vicinity of external objects, are chiefly derived 

 from this delicate and acute instrument of sensation. 4 



' The globe of the eye is contained within two coats, the 

 cornea and the sclerotica. The cornea is that circular trans- 

 parent membrane which covers a part of the anterior portion 

 of the eye, and through whose central part is seen the pupil. 

 It gives a passage to the rays of light, and presents the ap- 

 pearance of a dark circle, when contrasted with the white of 

 the eye. The remaining external covering of the organ is 

 formed by the sclerotic coat. This, where it is visible, is of 

 a bluish-white color, and is called the white of the eye. These 

 two coats together form a globe or ball, within which are con- 

 tained the immediate instruments of vision, consisting of the 

 iris, the humors of the eye, and the retina. The iris is that 

 colored circle which surrounds the pupil within the cornea, 

 and gives the peculiar color to the eye. It is an extremely 



