372 Dynamic Theory. 



The following may be named as examples of induced polar action in 

 bodies which were neutral or whose magnetism was in a state of bal- 

 anced tension : 



First. The action of the induction coil and other magnetic induction. 



Second. The building of crystals in a sluggish solution by the intro- 

 .duction of an active crystal. 



Third. The fermentation of saccharine substances, &c. , by the ac- 

 tion of ferments and digestion by diastase, ptyaline, gall, pancreatic 

 juice, gastric juice, bile, &c. 



Fourth. Segmentation following the consolidation of the sexual ele- 

 ments in reproduction. 



Fifth. Inoculation and fermentation by zymotic disease germs. 



CHAPTER XXXIX. 



SOUND. 



Sound is the sensation produced in us by the vibrations or pulsations 

 of the air or other ponderable bodies, liquid or solid, when such vibra- 

 tions are allowed to agitate the auditory nerve through the ear. Until 

 these vibrations reach the ear they are simply vibrations, not sound. l 

 They become sound through the medium of the auditory nerve and the 

 brain cells with which it connects, just as the rotary motion of a water 

 wheel becomes transformed into the vertical vibratory motion of a saw. 

 The movement of the wheel is not sawing, but as such movement is in 

 rapid sequence transferred to the saw, it becomes sawing in that instru- 

 ment. It has been settled by experiment that the rapidity of the vibra- 

 tions that make in us the sensation of sound, ranges from sixteen per 

 second to about 40,000 per second. These are the extremes; the limits 

 at both ends vary with different persons. The more rapid the vibrations 

 the higher the pitch of the sound. If the vibrations are regular and of 

 even length, the sensation is that of musical sound ; if uneven and 

 broken it is merely noise. Vibrations at the rate of 33 per second give 

 the sound of low C , sixty-six vibrations give the C of the next octave, 

 132 of the next, 264 of the fourth, 528 of the fifth, 1,056 of the sixth, 

 &c. , doubling for each octave ; the C at the beginning of the 8th octave 

 requiring 4, 224 vibrations for its expression. The beginning of the 

 12th octave requires 67,584 vibrations. But this rate of vibration is 

 beyond the perception of most human ears, and while it is vibratory 

 motion it is not sound, for it is not heard. Sounds, or the vibrations 

 which produce them, are propagated at different rates through different 



1 It is important to bear this in mind, although ordinarily the term, sound, is applied 

 also to the pulsations as they oecur outside of ourselves and so it will be in this chapter. 



