OPTICAL INSTRUMENTS. 



181 



in all, ten different parts, viz., the crystalline lens, vitreous 

 humor, cornea, retina in two parts, black pigment, choroid 

 or fleecy coat, iris, sclerotic or hard coat, optic nerve. The 

 first three are formed of glass, the other parts are of wood, 

 japanned and polished in appropriate colors, the whole sup- 

 ported on a neat mahogany stand. Price, $5.00. 



Fig. 695. Image on the fietina. (Fig. 695.) This 



consists of a hollow ball four inches in diame- 

 ter, representing the globe of the eye, having 

 inserted on one side a lens in a brass cell, 

 representing the lenses of the eye ; on the 

 opposite side of the ball there is a sliding tube 

 having on one end a ground glass. When the 

 lens representing the eye is held towards any 

 object, the inverted image may be seen on the 

 ground glass ; and by placing a concave or 

 convex lens in front of the lens in the instru- 

 ment, the effect of long and near sighted vision 

 is beautifully seen. Price, $2.50. 



Fig. 696. 



Instrument to show the nature of Vision. (Fig. 696.) 

 This instrument is mounted on a neat mahogany base 

 thirteen inches long, on which is supported from a short 

 pillar, a glass globe, four inches in diameter, having an 

 opening on two sides, about two inches wide : in one of 

 these apertures are represented the outer lenses of the eye ; 

 near the other end of the base is an object, about six inches 

 high, which is movable for about two inches, being fixed on 

 one side. To the object are attached nine silken strings, of 

 different colors, representing rays of light, and passing 

 through holes in the lenses of the eye, are united to an in- 

 verted image of the object, at the place of the retina. The 

 whole arrangement of strings attached to the erect object, 

 and crossing at the lenses of the eye and uniting the inverted 



VOL. II. 16 



