282 SOUND 



but I OCX) vibrations a second, and the deepest bass of men 

 falls but to 80 vibrations a second. 



While the human voice is limited in its production of sound, 

 rarely falling below 80 vibrations a second and rarely ex- 

 ceeding 1000 vibrations a second, the ear is by no means lim- 

 ited to that range in hearing. The chirrup of a sparrow, the 

 shrill sound of a cricket, and the piercing shrieks of a locomo- 

 tive are due to far greater frequencies, the number of vibra- 

 tions at times equaling 38,000 per second. 



264. The Musical Scale. When we talk, the pitch of the 

 voice changes constantly and adds variety and beauty to con- 

 versation ; a speaker whose tone, or pitch, remains too con- 

 stant is monotonous and dull, no matter how brilliant his 

 thoughts may be. 



While the pitch of the voice changes constantly, the changes 

 are normally gradual and slight, and the different tones 

 merge into each other imperceptibly. In music, however, 

 there is a well-defined interval between even consecutive 

 notes ; for example, in the musical scale, middle C (do) with 

 256 vibrations is followed by D (re) with 288 vibrations, and 

 the interval between these notes is sharp and well marked, 

 even to an untrained ear. The interval between two notes is 

 defined as the ratio of the frequencies ; hence, the interval be- 

 tween C and D (do and re) is |||, or |. Referring to Sec- 

 tion 263, we see^that the interval between C and E is f-f j}, or 

 f , and the interval between C and C' is |||, or 2 ; the in- 

 terval between any note and its octave is 2. 



The successive notes in one octave of the musical scale are 

 related as follows : 



Key of C CDEFGABC' 



No. of vibra- 

 tions per sec. 256 288 320 341 384 427 480 512 

 Interval f f I 1 I Y 2 



