216 GENERAL SCIENCE 



the length and tension the same, the pitch will be higher. 

 The wires of a piano show the application of these laws 

 of strings. They vary from strings of small diameter 

 and a few inches in length to quite large strings several 

 feet in length. The high notes are made by the short 

 strings, the low ones by the long strings. Test the truth 

 of these statements by experiments with a sonometer. 

 (Fig. 191.) 



The Voice. The larynx or voice is just below the 

 throat or pharynx at the top of the trachea. It is com- 

 posed of cartilages bound together by ligaments and 

 surrounding muscles. In the larynx are the vocal cords, 

 which are the chief organs of the voice. These cords are 

 folds of connective tissue placed in such a way that they 

 may be stretched at will across the opening. The pas- 

 sage of air causes them to vibrate, and sounds are pro- 

 duced. 



If we cut a small slit in a piece of sheet rubber and tie 

 it over one end of a tube, we will have a mechanism sim- 

 ilar to that which produces voice. When we blow through 

 the tube, a sound is produced which will become higher in 

 pitch as the tension on the rubber is increased. Many 

 animals have voice, but man alone possesses the power 

 to express his thoughts in articulate sounds or speech. 



The Hearing. Sound is transmitted from a vibrating 

 object to the ear by waves in the air. The .ear is the 

 organ of hearing. For convenience in description it is 

 divided into three parts, the external ear, the middle ear, 

 and the inner ear. (Figure 192.) 



The external ear is an irregularly folded cartilage cov- 

 ered with skin. Its shape is especially well adapted for 

 catching sound waves and directing them through the 

 auditory canal to the middle ear. At the inner end of the 



