180 



Introduction to the Study of Science 



room and light the mixture. Try the various colors in the light. 

 How does white appear? How do red, blue, green, and other colors 

 appear? What change is made in the yellow? What does this ex- 

 periment show as to the dependence of colors upon the nature of the 

 objects ? 



The light produced by the salt-alcohol flame is shown by the glass 

 prism to be yellow. Does this help you to understand why yellow 

 alone of all the colors tested seems to be normal ? Why does the white 

 of one's complexion become "ghostly white"? Do you think it 

 possible or probable that objects reflect only those colors which fall 

 upon them ? Or does it seem more probable that the color of an object 

 depends both upon the nature of the object and upon the quality of 

 the light falling upon it and in which it is seen? 



Exercise : What the prism shows. The following experiment will 

 bring out somewhat more clearly the important facts. Into a dark- 

 ened room admit through a nar- 

 row slit in a window shade a 

 beam of sunlight. Place across 

 its path a glass prism in such a 

 way as to deflect the light upon 

 a white screen (Fig. 54 A) . Have 

 the screen far enough from the 

 prism to display the colors well 

 spread out and as bright as pos- 

 sible. This experiment shows also that sunlight, which we usually 

 call white light, is really composed of many colors. With a second 

 prism, placed as in Fig. 54 B, this point will be emphasized. The 

 second prism combines the col- 

 ored rays into which the light 

 is decomposed by the first prism, 

 and throws on the screen a ray 

 of white light. 



The band of colors projected 

 on the screen by the prism is FIG. 54 B. The different colors as 

 called a spectrum. Note the anal y ze d by the first prism are synthesized 



into white light by the second prism. 



FIG. 54 A. Sunlight is analyzed by a 

 prism into different colors. 



arrangement of colors of the 

 spectrum, passing from red at one end through orange, yellow, green, 

 and blue to violet at the other end. Do the colors stand out clearly 

 and distinctly separate from one another? 



Pass through each color successively the pieces of colored paper 

 which you used in the experiment with the salt-alcohol light. Ob- 

 serve the intensifying effect of the yellow ray upon yellow paper ; but 



