54 LABORATORY EXERCISES 



parallel. A 3-sided prism is the best thing to use, but other 

 objects, such as a chandelier pendant, a cut-glass bowl, or a 

 many-sided perfume bottle made of thick glass, will do. On 

 a sunny day darken a room almost completely; then let a beam 

 of sunshine enter through a crack around the window shade. 

 Place the prism, or its substitute, in the path of the sunbeam, so 



that the spectrum of " rainbow" 

 colors will be thrown upon a 

 sheet of white paper placed on 

 the wall, the floor, or on a table. 

 Give the names of the colors in 

 their order. 



6. Mixing of Colored Light. 

 In this experiment you will need 

 a " color top." You can buy one 

 FIG 22 at a toy store, or ypu can make 



one as follows (Fig. 22) : 



Out of stiff cardboard cut a circle 8 cm. in diameter (3 in.), and in 

 the center make a square hole about 4 mm. on a side. Make a 

 peg and handle for the top out of a soft-wood stick about 5 cm. long and 

 6 mm. thick. Let the "peg" end remain as thick as the original 

 stick, but cut down the rest of the stick slightly, so that the cardboard 

 can slip down to a "stop" 1.5 cm. from the peg, but no closer. Have 

 the peg smoothly rounded, so that the top will spin evenly. The part 

 that is to hold the cardboard circle should be square in cross section, 

 so that the circle cannot turn on the stick. Round off the upper part 

 of the stick (the handle). The circle should be slipped over the handle 

 until it comes to the "stop," above the peg. By twisting the handle 

 between your thumb and second finger you can spin the top. 



c. Out of sheets of colored paper cut circles having the size 

 of the cardboard one. Use violet, blue, green, yellow, red, and 

 black paper. Make a round hole in the center of each circle, 

 and cut a slit from circumference to center. Take first a yellow 



