506 PHYSIOLOGY 



the tone of a musical instrument may be so harsh that there is very little 

 difference between it and a noise. 



i In a musical tone we can distinguish various characters or qualities : 

 [ (1) The loudness of a tone is determined by the amplitude of the vibra- 

 tions of which it is composed. If a violin string be bowed forcibly the 

 excursion of its string at each vibration is greater than when it is bowed 

 gently, and the amplitude of the corresponding alternating waves of sound 

 varies in proportion to that of the vibrating body by which they are started. 

 By attaching a pointed slip of paper to the end of a tuning-fork and so record- 

 ing its vibrations on a blackened surface, it is easy to see the connection 

 which exists between the amplitude of vibrations and the loudness of the 

 sound produced by the vibrating fork. 



(2) The pitch of a musical tone depends on the frequency of the vibrations 

 of which it is composed. By means of a siren we can determine the number 

 of vibrations corresponding to each note. As the speed of revolution of the 

 siren is increased, and therefore the number of interruptions per second of 

 the stream of air passing through the holes in its disc, the note appears to us 

 to rise continuously. If we take two tuning-forks, one vibrating at 100 times 

 per second and the other vibrating 200 times per second, the pitch of the 

 latter is observed to be considerably higher than that of the former. In 

 fact it forms the octave. If the number of vibrations is less than about 

 thirty per second no musical tone is produced, the individual vibrations 

 being perceived as a series of pulses in the surrounding air, and it is only 

 when we increase the number to about forty per second that we are able to 

 appreciate the pitch of the note produced. As the number of vibrations 

 per second is increased the note rises steadily without break till we arrive at 

 40,000 to 50,000 vibrations per second. Above this number of vibrations 

 the human ear is incapable of perceiving any note at all, though it is probable 

 that small animals can perceive notes still higher in the scale. In music 

 neither the lowest nor the highest tones are used. The lowest tones of the 

 large organs, that of the sixty-four foot pipe, is 16 vibrations per second, and 

 one can hardly speak of its effect as that of a musical tone. The highest 

 notes employed in music are a4 and c5 with 3520 and 4224 vibrations per 

 second on the piano, and d5 with 4752 vibrations on the piccolo flute. In 

 music therefore we only employ between 40 and 4700 vibrations per second, 

 i.e. about seven octaves. The manner of construction of the musical scale 

 will be dealt with later. 



(3) Timbre or quality of musical sounds. 



When the same note is sounded on different instruments, i.e. tuning-fork, 

 violin, piano, trumpet, human voice, every, person, whether he has an 

 educated musical ear or not, can say at once what kind of instrument is 

 being used. This fact shows that the sound wave produced by these 

 instruments must differ, altogether apart from any differences in amplitude 

 or in number of vibrations per second, and if the sound waves produced 

 by these instruments be recorded an actual difference is found in the 

 shape of the curve. 



