350 THE SENSES 



intricacy in some measure corresponds with the mathematical complexity 

 of the air-waves producing the sensations of tone and of noise which we 

 continually experience. 



CERTAIN QUALITIES OF SOUNDS. All sounds, practically speaking 

 (that from a tuning-fork is sometimes excepted), have within them ele- 

 ments both of tone and of noise. "No player of the violin avoids all 

 noise of scraping from the bow; no stroke of a workman's hammer or 

 slamming of a door that does not start and catch up into itself some trace 

 of musical sound." But noises for the most part remain unstudied 

 and their relation to the ears is almost unknown. They constitute, 

 however, especially in cities, no inconsiderable portion of the sounds with 

 which the ear has to do. 



Tones or musical sounds have three basal characteristics: intensity, 

 pitch, and quality (timbre). The intensity of a tone, depends wholly 

 upon the amplitude of the air-vibrations which move the membrana 

 tympani. This amplitude must not be confused with the frequency of 

 the vibrations, for it has nothing to do with it. 



The pitch of musical sounds (noises lack especially this quality) 

 depends wholly, so far as we know, on the number of vibrations per 

 second produced in the organ of Corti by the sonorous body. The 

 discrimination of differences in pitch varies very widely in different 

 persons. Some cannot distinguish between two contiguous whole tones, 

 while in some parts of the scale many musicians can distinguish differ- 

 ences dependent on one-third of a single vibration-number, a variation 

 of about 0.00066 per cent. 



This faculty of discriminating pitch-differences is in most persons cap- 

 able of a great degree of development, but by what parts of the ear this 

 improvement is accomplished is not known. The fact of its possibility 

 would seem to imply that the various muscles of the ear (perhaps fibers 

 in the ligamentum spirale among the rest) have much to do with auditory 

 adjustments, because the muscles are, to say the least, much more fully 

 under voluntary control than other sorts of tissue in the organism. 

 Many of the lower animals (e. g., cats and numerous sorts of insects) 

 can hear sounds far too high for the human ear, while others are very 

 sensitive to jars we should not notice. Recent highly valuable writings 

 of Helen Kellar (learned and capable, although deaf and blind) reveal 

 how much the jars and unsonorous vibrations of things of our environ- 

 ment may teach us when they have a chance. They were partly repre- 

 sented in the auditory nerve, although largely it appears by the kines- 

 thetic sense-organs in the joints and muscles. 



The quality of tones, technically called timbre, depends on many 

 various conditions, part of which are unknown. The difference in the 

 quality of tones is illustrated in the uniqueness of each human voice 

 and by the variations in the same note when sounded, for instance, on a 

 violin, a cornet, a piano, an organ, and a harp. Another sort of qualita- 

 tive difference is expressed by the word volume, illustrated by the differ- 

 ence between the sound of a vocal solo and that of a chorus, or between 



