SOUND. 



sounds. It is nevertheless certain, that all vibrations, in pro- 

 portion as they are regular, uniform, and equal, produce sounds 

 proportionably more agreeable and musical. 



Sounds are distinguished from each other by their pitch or 

 tone, in virtue of whichthey are high or low ; by their intensity, 

 in virtue of which they are loud or soft ; and by a property ex- 

 pressed in French by the word timbre, which we shall here adopt 

 in the absence of any English equivalent. 



6. The pitch or tone of a sound is grave or acute. In the 

 former case it is low, and in the latter high, in the musical scale. 



The more rapid the vibrations are, the more acute will be the 

 sound. A bass note is produced by vibrations much less rapid 

 than a note in the treble. 



All vibrations which are performed at the same rate produce 

 waves of equal length and sounds of the same pitch. 



7. The intensity of a sound, or its degree of loudness, depends on 

 the force with which the vibrations of the sounding body are made. 



8. The timbre of a sound is not easily explained, and still less 

 easily can the physical conditions on which it depends be ascer- 

 tained. If we hear the same musical note produced with the 

 same degree of loudness in an adjacent room successively upon a 

 flute, a clarionet, and a hautboy, we shall, without the least 

 hesitation, distinguish the one instrument from the other. Now 

 this distinction is made by observing some peculiarity in the notes 

 produced, yet the notes shall be the same, and be produced with 

 equal loudness. 



9. It is manifest from the absence of all confusion in the effects 

 of music, at whatever distance it may be heard, that in the same 

 medium all sounds have the same velocity. If the different 

 notes simultaneously produced by the various instruments of 

 an orchestra moved with different velocities through the air, 

 they would be heard by a distant auditor at different moments, 

 the consequence of which would be, that a musical performance 

 would, to the auditors, save those in immediate proximity 

 with the performers, produce the most intolerable confusion 

 and cacophony ; for different notes produced simultaneously, and 

 which, when heard together, form harmony, would at a distance 

 be heard in succession ; and sounds produced in succession would 

 be heard as if produced together, according to the different velo- 

 cities with which each note would pass through the air. 



1 0. The velocity of sound varies with the elasticity of the medium 

 by which it is propagated. Its velocity, therefore, through the air 

 will vary, more or less, with the barometer and thermometer. 



The experimental methods which have been adopted to ascertain 

 the velocity of sound are similar in principle to those which have 

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