QUALITIES OF SOUND. 597 



This peculiar quality, which is independent of the pitch (i.e., 

 rate of vibration) or the intensity (i.e., amplitude of wave), is 

 called the color or timbre of the note. It depends on the number, 

 the variety, and the relative intensity of the over-tones or har- 

 monics, which accompany the notes. So that really the timbre 

 or quality of a note, and therefore the special characters of the 

 different musical instruments, is produced by their impurity, or 

 the complexity of the over-tones which aid in producing them. 



All elastic bodies can vibrate, and therefore are more or less 

 capable of conducting sounds. Sound vibrations can be trans- 

 mitted from one body to another placed in contact with it. From 

 a hard material the waves are readily communicated to the air, 

 and this is the ordinary medium by means of which sound is trans- 

 mitted and finally arrives at our organs of hearing. The old ex- 

 periment of placing a small bell under the glass of an air-pump 

 and making the tongue strike it after the air has been removed, 

 shows that the medium of the air is essential for the transmission 

 of the sound vibrations. 



The transmission of waves of sound from the air to more dense 

 materials, such as those which surround our auditory nerve-ter- 

 minals, takes place with much greater difficulty than that from 

 a solid to the air, and we find a variety of contrivances by which 

 the gentle waves, arriving at the ear by the air, are collected and 

 intensified on their way to the labyrinth. 



But the medium of the air is not necessary in order that sound 

 may reach the internal ear. Nor is the. route through the outer 

 canal, and the drum and its membrane, the only one by which 

 the vibrations can arrive at the cochlea. The solid bone which 

 surrounds the labyrinth is in direct communication with all the 

 bones of the head, and the sound can travel along these bones 

 and reach the nerve-endings. This can easily be proved by placing 

 the handle of a vibrating tuning fork against the forehead, or 

 better still, against the incisor teeth. The sound, although pre- 

 viously hardly audible, at once becomes quite distinct, or even 

 appears loud. 



This direct conduction through the bones of the head is, under 

 normal conditions, of little use to man ; but attempts have been 



