384 ELEMENTARY PHYSIOLOGY less. 



of events, the consequence of the last of which is the 

 sensation of sound. 



Every sound consists, as we have seen, of vibrations. 

 Sometimes the vibrations are repeated with great regu- 

 larity ; and sounds, in which the regular recurrence of 

 the same vibrations is conspicuous, are called " musical 

 sounds." Sometimes no regular repetition of vibrations 

 can be recognised ; the sound consists of vibrations, few 

 of which are like each other, and which fall irregularly on 

 the ear ; such sounds are called '• noises." 



When we listen to musical sounds, each set of regularly 

 repeated vibrations generates in tlie central end-organ a 

 particular kind of sensation which we call a tone ; and tlie 

 simultaneous or successive production of different tone- 

 sensations gives rise in us to the feelings which we speak 

 of as those of harmony or melody. 



When we listen to a noise the vibrations generate 

 sensations which are of a certain intensity, according to 

 which we call the noise slight or great, low or loud, and 

 which also have certain characters by which we recognise 

 the kind of noise ; but the sensations have not the quali- 

 ties of tone-sensations, and do not give rise to feelings of 

 melody or harmony. 



A pure musical sound consists of a series of vibra- 

 tions repeated with exact regularity, the number of 

 vibrations occurring in a given time, e.g. in a second, 

 determining what is called tlie pitch of the " note." But 

 ordinary musical sounds are, for the most part, not simple, 

 consisting of one set of vibrations, but compound, con- 

 sisting of several sets of vibrations occurring together ; 

 in these musicians distinguish one set, called the funda- 

 mental tone, and other sets, varying in intensity or 

 loudness, called overtones. 



A tuning-fork, when set vibrating, vibrates with a 

 given rapidity ; and the note given out is determined by 

 the rapidity of the vibration, by the number of vibrations 

 repeated, for instance, in a second ; hence every tuning-fork 



