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 Ioil\ the latter a 

 high note ; designations which in all probability 

 were originally derived from the visible motions 

 of the throat of a person who is singing these 

 different notes ; for, independently of this cir- 

 cumstance, the terms of high and low^ are quite 

 arbitrary ; and it is well 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 

 cord 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 cord or wire. In a wind instrument, the 

 tone depends altogether upon the length of the 

 tube producing the sound. 



There are, therefore, two qualities in sound 

 recognisable by the ear, namely, loudness, or 

 intensiti/, and quality, or tone ; the former de- 



