496 STUDIES IN ADVANCED PHYSIOLOGY. 



superiority of the ear as an organ for catching sound several 

 octaves higher and lower than the piano is at once apparent. 

 The compass of the human voice is about three octaves 

 only. Deep F of the bass singer has about 87 vibrations, 

 and the upper G of the soprano about 775 vibrations per 

 second. Voices exceed these limits only in very excep- 

 tional cases. It will be pointed out later that the limits of 

 the ear are not limits imposed by the vibrations themselves, 

 but that these limits are produced in consequence of the 

 anatomy of the ear, the basilar membrane having an extent 

 of about thirteen octaves only. It is, of course, entirely 

 possible, in fact probable, that an anatomical extension of 

 this structure in the ear would have materially increased the 

 range of the musical scale which might be perceived. 



THE TRANSMISSION OF SOUND IN THE AIR AND ITS VELOCITY 



IN THE SAME. 



The usual medium for the transmission of sound is, of 

 course, the air. Sound is unable to pass through a vacuum. 

 A sounding body placed under a bell jar of an air-pump and 

 the air then exhausted, cannot be heard, no matter how 

 violently it may be in motion. The admission of air into 

 the receiver, and so the formation of a medium around it 

 for the transmission of sound at once makes the sound loud 

 and clear. Sound waves in air differ, however, in form from 

 those produced by the tuning-fork or a string. The sound 

 waves in air go in all directions from the sounding point 

 in the form of concentric spheres, somewhat like the circles 

 that radiate from the surface of a body of water from the 

 point where a pebble has been thrown into it. In the case 

 of the air, these waves do not extend in the form of circles 

 but in the form of spheres. In a sound wave the particles 

 of air are set in motion in such a way that they produce 

 spheres of condensed air and rarefied air, and it is these 

 waves of condensation and rarefaction that are transmitted, 

 and, of course, not the particles of air themselves. 



