596 PHYSIOLOGY 



each stick corresponds to a distinct note, and tunes may be played on such 

 a collection of sticks. 



SOUND ANALYSIS can be performed in a number of ways ; possibly the 

 simplest method is to record the excursions of a flexible diaphragm on a rota- 

 ting wax cylinder, as in the phonograph. When thus recorded, sound waves 

 are found to have a regular sequence when they consist of tones and an 

 irregular sequence when they are noises. Sources of sound which produce 

 the former therefore vibrate in a regular manner (for example the limbs of 

 a tuning-fork, or the air in an organ pipe), while those which produce the latter 

 vibrate irregularly (e.g. a cart over cobbles). 



INTENSITY AND PITCH. In a similar manner loudness or intensity 

 is found to depend on amplitude (as in the case of light), while pitch depends 

 on the wavelength, short waves having a high, long waves a low pitch. This 

 can be proved in other ways : thus, if a violin string be bowed forcibly the ex- 

 cursion 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. 



That the pitch of a tone depends on the frequency of the vibrations, is 

 shown by means of the syren and the klaxon. As the speed of rotation 

 increases, and therefore also the number of impulses imparted to the air 

 per second, so the note appears to us to be rising. Since sounds of high 

 and low pitch travel with the same speed, the distance between the 

 waves decrease as the number of impulses per second increases. 



LIMITS OF PITCH. The ear is unable to perceive tones the pitch 

 of which falls above or below certain fairly well-defined limits. 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 tone of large organs, that 

 of the sixty-four foot pipe, is 1 6 vibrations per second, and one can hardly 

 speak of its effect as that of a musical tone. The highest notes employed 

 in music are 04 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. 



SOUND AUGMENTORS. Experiment shows that the intensity of the 



