RELATION OF AIR TO SOUND 



19 



the same pitch, there is something about each that 

 makes it different from the other. We can always tell 

 a cornet from a trombone by the sound of the tones 

 which they give out. The musician would say that the 

 piano tone has a different quality from the violin tone. 

 Difference in quality is due to blending of the over- 

 tones with the fundamental tone. 



Sounds of great intensity may produce chemical 

 changes. It has been discovered that several chemical 

 substances may be broken down or otherwise changed 

 chemically if they are subjected to sound waves of 

 great intensity and usually of very high pitch. One of 

 the most spectacular effects reported by the investi- 

 gators was the apparent soft-boiling of an egg by 

 these so-called super-sonic sound waves without the 

 raising of the temperature. 



How is the human ear constructed for hearing? It is 

 one of the most sensitive and delicate organs of the 



Inner Middle 

 ear car 



itirrup 

 nvil 



External 

 ear 



C 

 . TH 



E HUMAN EAR 



human body, having for its purpose the changing of 

 sound waves into nerve currents which are carried to 

 the brain. To show the delicacy of this organ as I 

 write I hear the ticking of a clock, the sounds of the 

 motor and the horn of an automobile, the scratch of 

 my pen on the paper, and the shrill note of a song 

 bird all at the same instant, and yet my ear takes each 

 air vibration, separates it from the others, and sends 

 the impulses to the brain. 



As the diagram (Fig. 36) shows, the human ear is 

 made up of three parts, the outer ear, the middle ear, 

 and the inner ear. Sound waves are gathered by the 

 outer ear and directed into the outer canal, where they 

 strike against the eardrum, setting it in vibration. 

 The middle ear is a cavity in which are three bones 

 known as hammer, anvil, and stirrup because they re- 

 semble these devices in shape. The hammer rests 

 lightly against the eardrum and the anvil. The anvil 

 in turn rests against the stirrup, which presses against 

 the membrane of the inner ear. The inner ear contains 

 a liquid which is enclosed in a case of bone. The 

 nerves from the brain end here in the inner ear. 



As the eardrum is set in vibration the bone bridge 

 of hammer, anvil, and stirrup takes up the impulse and 



carries it to the membrane of the inner ear, which also 

 vibrates, setting the liquid in motion. From nerve 

 endings that are highly sensitive to the vibrating 

 liquid, a nerve current is sent along the nerves to the 

 _braku 



Also located in the inneTTnu aio Uie_gernicircular 

 canals which are shown in the diagram (Fig. 

 These have to do with our sense of balance. 



Since the ear is such an important organ and since 

 it is so delicate and sensitive, we should give it great 

 care. Deafness may result from mistreatment. Wax 

 which is found in the ear should never be removed 

 with a sharp instrument, as there is danger of punc- 

 turing the ear drum. Take care never to blow the 

 nose too hard or suddenly, for it is often this that 

 forces some infection into the ear. Never slap any- 

 one over the ear. When in swimming, plug the ears 

 with cotton. In case of severe earache it is always best 

 to call the doctor. If these few simple rules are fol- 

 lowed you are not likely to have serious ear trouble. 



How may different tones be produced on musical 

 instruments? The instruments of an orchestra illus- 

 trate clearly the different ways in which music may be 

 produced. The drums produce their tones when a 

 tight membrane is struck a sharp blow with a padded 

 stick. The violins, violas, cellos, and bass viols send 

 out their tones when strings are set in vibration by 

 bowing. The horns such as the cornet, trombone, and 

 French horn contain air columns which are set in mo- 

 tion by the vibration of the player's lip as air is forced 

 past it into the horn. The clarinet, oboe, and saxo- 

 phone contain air columns which are set in vibration 

 by reeds held in the lips of the player. The organ is a 

 group of air columns which are set in vibration by 

 forcing air past an opening in the pipe. 



The pitch of the tones sent out by stringed instru- 

 ments is changed by changing the length of the string. 

 When a violin player places his finger at a certain 

 point the string will produce a note of given pitch. If 

 he shortens the string the pitch will be raised, while 

 a longer string will produce a lower tone. Observe 

 the strings in a piano. The lowest note produced by 

 striking the last key comes from a string which is 

 long and very heavy. This makes about 32 vibrations 

 per second. The highest note comes from a short, 

 tightly stretched string and gives a tone of about 4,000 

 vibrations per second. 



The human voice is produced by two cords or 

 strands which are stretched over the vocal box in the 

 larynx. As air from the lungs moves past them they 

 are set in vibration, giving out tones that are shaped 

 and moulded by the tongue, cheeks, and lips. The 

 pitch of the tones of the vocal cords is changed by 

 muscles that make them tighter or less tight. 



Instruments which depend for their tones upon vi- 



