20 



THE OCEAN OF AIR. 



brating air columns change their pitch by changing 

 the length of the air column. This is shown clearly in 

 the tin fife or flute. The holes which are covered with 

 the fingers make it possible to change at will the 

 length of the column of air that the instrument en- 

 closes. A long air column produces a tone of low pitch 

 while the short ones produce tones of higher pitch. 



How does the phonograph reproduce sound? The 

 phonograph is an interesting musical device that has 

 found its way into many homes over the world. It 

 applies many of the principles which have been stud- 

 ied in this topic. A phonograph record is made by 

 recording sound vibrations in a disk of wax by cut- 

 ting either into the sides of a spiral groove or into its 

 bottom. The sound waves are picked up and made to 

 vibrate a cutting needle which cuts little pieces from 

 the side or bottom of the groove, thereby recording 

 the series of vibrations. If a -record is looked at with 

 a magnifying glass these cuts may be seen. The dia- 

 gram (Fig. 37) shows how they appear. 



In the reproduction 

 of the sound by the 

 phonograph the process 

 is reversed. The disk is 

 turned and a needle 

 which follows the 

 groove is caused to vi- 

 brate by the little in- 

 dentations that were 

 cut into the sides or bot- 

 tom. The needle then 

 causes a disk of rubber 

 to vibrate; in turn the 

 air column of the horn 

 is set in vibration and 

 we hear the original sounds which were recorded on 

 the record. The diagram (Fig. 38) shows the two 

 types of reproducing mechanisms in use. The me- 

 chanism represented at a is used when the cuts are 

 made in the side of the groove and that at b is used 

 when they cut into the bottom. 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, pp. 419-430 



Clement, Collister, and Thurston, Our Surroundings, pp. 170- 

 179 



Hunter and Whitman, Science in Our World of Progress, pp. 

 300-305 ; Science in Our Social Life, pp. 300-305 



Lake, Harley, and Welton, Exploring the World of Science, 

 pp. 50-65 



Pieper and Beauchamp, Everyday Problems in Science, pp. 

 592-601 



Powers, Neuner, and Bruner, Man's Control of His Environ- 

 ment, pp. 505-518 and 565-566 



FIG. 37 



Van Buskirk and Smith, The Science of Everyday Life, pp. 

 31-39 



Watkins and Bedell, General Science for Today, pp. 414-419 



Webb and Beauchamp, Science by Observation and Experi- 

 ment, pp. 633-645 



Wood and Carpenter, Our Environment: How We Use and 

 Control It, pp. 122-136 



FIG. 38. PHONOGRAPH REPRODUCING MECHANISMS 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. What sound is and how it is transmitted through 

 various substances. 



2. How the human ear is constructed and how the 

 various parts working together produce the sensa- 

 tion of sound. 



3. Something of how the ear should be cared for. 



4. How musical instruments which use strings are 

 constructed and how they produce tones of varying 

 pitch. 



5. The construction and operation of some musical 

 instruments which use vibrating air columns. 



TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements, answer the 

 questions, and comply with the instructions. 



1. Sound is produced whenever anything 



2. Name the three best conductors of sound. 



3. Sound travels (more, less) __ rapidly on a warm 

 day than on a cold day . 



4. The outer ear directs sound waves into the , where 



they strike against the and cause it to vibrate. The 



middle ear contains three bones called 



_, and 



These bones convey the vibration to the inner ear, which 



contains a Nerves carry the sensation from the inner 



ear to the - 



5. A noise is produced by vibrations, and a musical 



tone is produced by vibrations. 



6. In making a phonograph record, what do the sound 

 waves cause to vibrate? From what are pieces cut? 



7. When a phonograph is played, what is caused to vi- 

 brate by the grooved disk? What is the direct cause of the 

 vibration of air in the horn? 



8. The slide trombone produces tones of different . 



