4:12 DIFFERENCES IN TONES, AND IN SENSE OF HEARING. 



upon the force and extent of the vibrations communicated by 

 the sounding body to the air. Thus, when we draw the 

 middle of a tight string far out of the straight line, and then 

 let it go, a loud sound is produced, and we can see that the 

 space through which the string passes from side to , side is 

 considerable. As the extent of the vibrations of the string 

 diminishes^ the sound becomes less powerful ; and when we 

 can no longer see the vibrations, but can only feel them, the 

 sound is faint. The length of the undulations in the air 

 corresponds with that of the vibrations in the sounding 

 body ; and consequently they will strike upon the tympanum 

 with more or less force, according as these are longer or 

 shorter. The cause of the differences in the timbre or quality 

 of musical tones, such, for instance, as those which exist 

 between the tones of a flute, a violin, and a trumpet, all 

 sounding a note of the same pitch, are unknown ; but they 

 probably depend upon the different form of the vibrations. 



525. The faculty of hearing, like that of sight, may be very 

 much increased in acuteness by cultivation ; but this increase 

 depends rather upon the habit of attention to the faintest 

 impressions made upon the organ, than upon any change in 

 the organ itself. This habit may be cultivated in regard to 

 sounds of some one particular class ; all others being heard as 

 by an ordinary person. Thus the watchful North American 

 Indian recognises footsteps, and can even distinguish between 

 the tread of friends or foes, whilst his companion who lives 

 amid the busy hum of cities is unconscious of the slightest 

 sound. Yet the latter may be a Musician, capable of distin- 

 guishing the tones of all the different instruments in a large 

 orchestra, of following any one of them through the part 

 which it performs, and of detecting the least discord in the 

 blended effects of the whole, effects which would be, to his 

 coloured companion, but an indistinct mass of sound. In the 

 same manner, a person who has lived much in the country is 

 able to distinguish the note of every species of bird which 

 lends its voice to the general concert of .Nature ; whilst the 

 inhabitant of a town hears only a confused assemblage of 

 shrill sounds, which may impart to him a disagreeable rather 

 than a pleasurable sensation. Of the direction and distance 

 of sounds, our ideas are for the most part formed by habit. 

 Of the former we probably judge, in great degree, by the 



