182 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



object, may be moved beyond the retina, as in the long- 

 sighted eye ; or within the retina, as in the near-sighted 

 eye ; or when placed at the retina, perfect vision ; thus ex- 

 plaining, in a clear manner, those positions of the image in 

 regard to the retina. Price, $6.00. 



Fl s- 697. Muscles of the Eye. 



(Fig. 697.) This in- 

 strument represents the 

 globe of the eye revolv- 

 ing in its socket, and 

 consists of a ball, about 

 four inches in diame- 

 ter, having attached to 

 it stout pieces of tape, 

 representing its four 

 straight and two ob- 

 lique muscles, having their proper names attached ; also 

 showing the beautiful arrangement of the oblique muscle 

 near the nose, giving a correct idea of that wonderful ar- 

 rangement in the human frame. The ball of the eye may 

 be moved in all directions. The whole is mounted on a 

 neat mahogany stand, about 12 inches long. 



Price, - $2.50. 



" or the whole set, - $13.00. 

 first, third, and fourth, $11.00. 



The Prism. (Fig. 698.) A 

 triangular piece of glass employed 

 to separate a ray of light into its 

 constituent parts or colors by re- 

 fraction. The prism is the instru- 

 ment by which the most remarkable 

 phenomena of light and colors are 

 exhibited. To use the prism, let a 

 room be darkened, and the sun 

 permitted to shine into it through 

 a small hole in the window shutter, 



it will give a circular white spot ; but let it be made to fall 

 on the glass prism, then will the sun's rays in passing 

 through the prism suffer different degrees of refraction, and 

 by that means be parted into different rays, which being 

 received upon a sheet of white paper will exhibit the follow- 



