122 TERRESTRIAL ADAPTATIONS. 



These differences are produced by the different 

 rapidity of vibration of the particles of air. The 

 gravest sound has about thirty vibrations in a 

 second, the most acute about one thousand. 

 Between these limits each sound has a musical 

 character, and from the different relations of 

 the number of vibrations in a second arise all the 

 differences of musical intervals, concords and 

 discords. 



4. The quality of sounds is another of their 

 differences. This is the name given to the dif- 

 ference of notes of the same pitch, that is the 

 same note as to acute and grave, when produced 

 by different instruments. If a flute and a violin 

 be in unison, the notes are still quite different 

 sounds. It is this kind of difference which dis- 

 tinguishes the voice of one man from that of 

 another : and it is manifestly therefore one of 

 great consequence: since it connects the voice 

 with the particular person, and is almost neces- 

 sary in order that language may be a medium of 

 intercourse between men. 



5. The articulate character of sounds is for us 

 one of the most important arrangements which 

 exist in the world ; for it is by this that sounds 

 become the interpreters of thought, will and feel- 

 ing, the means by which a person can convey his 

 wants, his instructions, his promises, his kindness, 

 to others ; by which one man can regulate the 

 actions and influence the convictions and judg- 

 ments of another. It is in virtue of the pos- 



