1S8 SENSE OF HEARING. 



acute, from eight thousand one hundred and ninety-two vibrations, ac- 

 cording to some; twelve thousand, according to others. Some well- 

 devised experiments, however, made by M. Savart, largely extend these 

 limits, and appear to indicate that they cannot be esteemed rigidly 

 fixed. In his experiments, the ear distinctly appreciated fourteen or 

 sixteen vibrations, or seven or eight impulses per second; and the acutest 

 note that was audible proceeded from upwards of forty thousand vibra- 

 tions, or more than twenty thousand impulses per second. Recently, 

 M. Despretz 1 has determined, that classifiable sounds are comprised 

 between the limits of 32 simple vibrations for the lowest tone, and 

 73,000 for the highest. 



The duration of the impression of a sonorous vibration on the ear 

 has been estimated at about the sixteenth part of a second; but it is 

 difficult to determine it exactly. 



If a sonorous body be struck, and the vibrations excited be all per- 

 formed in equal times, a simple and uniform sensation is produced on 

 the auditory nerve, and one musical tone is heard. But if the vibrations 

 be various and irregular, they fall scatteringly on the organ of hearing, 

 and excite a harsh impression, as if various sounds were heard together. 

 In other words a noise or discord is produced. If two notes, sounded 

 together, afford pleasure, they produce harmony or concord. This arises 

 from the agreement of the vibrations, so that some of them strike upon 

 the ear at the same time. If, for example, the vibrations of one sono- 

 rous body take place in double the time of another, the second vibration 

 of the latter will strike upon the ear at the same instant as the first 

 vibration of the former. This is the concord or harmony of an octave. 

 Between a note and its octave, there are six intermediate notes, consti- 

 tuting the diatonic -scale or gamut. If the vibrations of two strings are 

 as two to three, the second vibration of the former will correspond with 

 the third vibration of the latter, producing the harmony called a fifth. 

 There are other tones, which, although they cannot be struck together 

 without producing discord, if produced in succession, give the pleasure 

 called melody. Melody is, in truth, nothing more than the effect pro- 

 duced on the brain by pleasing musical tones sounded in succession. 



There is another quality of sound whieh the French call timbre. 

 By some of the translators of the works of the French physiologists 

 and physicists this word has been rendered note. It is essentially dif- 

 ferent from note or tone; and is peculiar. By English philosophers it 

 is termed quality of sound. It is this quality that enables us to recog- 

 nise various instruments, when giving forth the same note or tone; 

 and to distinguish the voices of individuals from each other. Its cause 

 is not evident, but is conceived to depend upon the nature of the sono- 

 rous body, if it be a surface, and at the same time on its shape, if a 

 tube. M. Biot conjectures, that it is owing to the series of harmonic 

 sounds that form part of every appreciable sound. When any sonorous 

 body is made to vibrate, a distinct sound is heard, which is the funda- 

 mental; but, if attention be paid, others are heard at the same time. 

 These are called harmonics; and it is not improbable that timbre or 



1 Comptes Rendus, xx. 1214, cited by Longet, Traite de Physiologic, ii. 136, Paris, 1850. 



