64 MUSICAL SOUNDS 



LESSON 30. 



Nature of Musical Sounds. 



Ten'sion, act of stretching, state of being stretched. 



Grav'ity, in music, the moditicalion of any sound, by which it be- 

 comes deep or low in respect of some other sound. 



Con'cert, many performers playing the same tune. 



Line, a small French measure, containing the 12th part of an inch*. 

 geometricians conceive the line subdivided into six points. 



If a sonorous body be struck in such a manner, that its 

 vibrations are all performed in regular times, the vibrations 

 of the air will correspond with them ; and striking in the 

 same regular manner on the drum of the ear, will produce 

 the same uniform sensation on the auditory nerve and ex- 

 cite the same uniform idea in the mind ; or, in other words, 

 we shall hear one musical tone. But if the vibrations of the 

 sonorous body are irregular, there will necessarily follow a 

 confusion of aerial vibrations ; for a second vibration may 

 commence before the first is finished, meet it half way on its 

 return, intercept it in its course, and produce harsh jarring 

 sounds which are called discords. But each set of these 

 irregular vibrations, if repeated at equal intervals, would pro- 

 duce a musical tone. It is only their irregular succession 

 which makes them interfere, and occasions discord. 



The quicker a sonorous body vibrates, the more acute, or 

 sharp is the sound produced ; and the vibrations of the same 

 string, at the same degree of tension, are always of a similar 

 duration. Striking the note in quick succession, produces 

 a more frequent repetition of the tone, but does not increase 

 the velocity of the vibrations of the string. The duration 

 of the vibrations of the strings or chords depends upon their 

 length, their thickness, or weight, and their degree of ten- 

 sion. The difl'erent length and size of the strings of mu- 

 sical instruments, therefore, serve to vary the duration of the 

 vibrations, and consequently the acuteness or gravity of the 

 notes. 



Among the variety of tones, there are some which, sounded 

 together, please the ear, producing what we call harmony or 

 concord. This arises from the agreement of the vibrations 

 of the two sonorous bodies ; so that some of the vibrations 

 of each strike upon the ear at the same time. If the vibra- 



