274 INTRODUCTION TO GENERAL SCIENCE 



b. Look steadily for one minute at the red card, and then 

 immediately look at a white paper or wall. What color do 

 you see? You will remember that white is composed of all 

 the other colors. Now the eye is tired from seeing one color, 

 and responds to the other colors contained in the white. The 

 blending of these other colors is what produces the apparent 

 color. Repeat with the other cards, and tabulate your results. 

 The color which appears to be present on the white is called 

 the complementary color of the original color. 



200. SOUND AND HEARING 



Sound is caused by some material body moving to and fro, 

 that is, vibrating at least sixteen times a second. Impulses 

 are sent out which are conveyed by the air. There must be 

 some material medium, or sound will not be carried from its 

 source. Liquids carry sound better than gases, and solids 

 better than liquids. In each case, usually, the sound must 

 originate in the medium which is to convey it. We receive 

 the sensation, which we call sound, due to the beating of the 

 vibrations of the air upon the eardrums, which, in turn, con- 

 vey the vibrations within, to the nerves. Vibrations coming 

 at regular intervals are musical sounds; other vibrations 

 cause merely noise. 



As we understand it, sound is the sensation, and, while the 

 vibrations would exist even if there were no ears to hear, yet 

 sound does not exist outside of the nervous system. In this 

 respect, sound and light are similar, both are sensations. 



References : 



1. 1501 : 325-330. The Ear and Hearing. 



2. 1501:349-353. The Voice. . 



3. 1503:421-422. The Organ of Hearing. 



