OPTICAL INSTRUMENTS. 183 



ing colors, viz. red, orange, yellow, green, blue, indigo, and 

 violet ; and if the whole spectrum or image be divided into 

 360 equal parts, the red will occupy 45 of them, the orange 

 27, the yellow 48, the green 60, the blue 60, the indigo 40, 

 and the violet 80. 



Place the prism horizontally near the eye, with one of its 

 faces upwards so as to receive the light that enters on the 

 opposite face, and the following remarkable phenomena will 

 be observed ; the light will have undergone considerable 

 deviation, so that all objects will appear elevated towards 

 the summit of the prism, and will appear colored at their 

 edges with all the colors of the rainbow. If the face of 

 the prism is downward the objects will be displaced down- 

 ward. If the prism be placed vertically, the deviation will 

 take place to the right or left as the position is altered. 



Price, 38 cts. ; $1.00 ; $1.50 ; $2.00 and $3.00. 

 " mounted (Fig. 698), $2.00 to $5.00. 



Compound Prisms. Prisms are sometimes formed of 

 different kinds of glass, as crown, flint, and plate glass, for 

 showing their different refractive powers. 



Price, $3.00. 



Instrument for the decomposition Fi s- 699 - 



of Light. (Fig. 699.) This instru- 

 ment for the recomposition of light, 

 sometimes called a color blender, is 

 conveniently formed in the shape of 

 a large top, about five and a half 

 inches in diameter, which, by means 

 of a string and handle, may be 

 rapidly spun around for a considerable time. On the sur- 

 tace of the top there is accurately described the proportion 

 of the different colors, which are engraved on a plate, near 

 the centre, while the exterior is filled with colored papers, 

 each color of nearly the color of the spectrum, and occupy- 

 ing the same proportion, viz. violet 80, indigo 40, blue 60, 

 green 60, yellow 48, orange 27, red 45 ; the whole is var- 

 nished to protect it from injury. 



As the rays of the sun may be separated into these seven 

 primitive colors, so, by their mixture in due proportions, 

 may white be produced. White, therefore, is the mixture 



