HEARING. 419 



become so blended together as not to be dis- 

 tinguishable from one another, and the sensation 

 of a uniform continued sound, or musical note, 

 is excited in the mind. If the intervals between 

 the vibrations be long, the note is grave ; if short, 

 that is, if the number of vibrations in a given 

 time be great, the note is, in the same proportion, 

 acute. The former is called a low, the latter a 

 high note ; designations which were perhaps 

 originally derived from the visible motions of the 

 throat of a person who is singing these different 

 notes ; for, independently of this circumstance, 

 the terms of high and low are quite arbitrary ; 

 and it is wxll known that they were applied by 

 the ancients in a sense exactly the reverse of 

 that in which we now use them. 



The different degrees of tension given to the 

 chord or wire of a stringed musical instrument, 

 as well as its different lengths, determine the 

 frequency of its vibrations ; a greater tension, or 

 a shorter length, rendering them more frequent, 

 and consequently producing a higher note ; and 

 on the contrary, the note is rendered more grave 

 by either lessening the tension, or lengthening 

 the chord or wire. In a wind instrument, the 

 tone depends chiefly upon the length of the tube 

 producing the sound. 



There are, therefore, two qualities in sound 

 recognisable by the ear, namely, loudness, or 

 intensity, and quality, or tone ; the former de- 



