the modern miracles of sound motion pictures and radio open a vast sources of entertainment and instruction to benefit from these we need our ears which interpret for us the multitude of sound waves they receive now if you will lend me your ears while watching this picture on the screen i will tell you about these invisible waves and how our ears are able to convert them into sound we all know that if a pebble is dropped into water ring like ripples spread in all directions over the surface a doorbell ringing sends out similar but invisible wave like impulses which travel through the air with the speed of about eleven hundred feet per second sounds of every kind are transmitted to our ears by just such waves even now as my voice comes to you it is carried by these air waves to be conveyed to your own brain by nerve impulses created within your ear as we shall see the speed of conversion requires a highly refined and perfect mechanism which is our ear to begin with  impulses are caught by the outer shell and directed into the air can now now let us look into this canal by using a specially designed instrument like this photo scope which is used by physicians when examining our ears there in the center we see a small disk which is the drum membrane now here it is a very close range and very much enlarged sound waves beat against this membrane as drum sticks beat upon a kettle drum tympanum so it is naturally called late in panic membrane it lies a little more than an inch from the outer opening and completely shuts off the ear drum from the air canal just as a drum head completely covers a drum hidden immediately beyond this barrier lies the oddly shaped and highly specialized organ which by far surpasses any instrument of human invention in its ability to detect and to interpret sounds of every conceivable kind and degree it is indeed rightly called the most remarkable mechanical system in the human body important connecting passage opens just above the console like other important sense organs the air lies close to the brain all sound waves entering the ear are converted into nerve impulses these impulses are conveyed to the brain by the now let us greatly enlarge the picture of one ear so that we may examine its construction and its parts in greater detail in the sectional view the air is divided into three parts first the external or out or air consisting of a shell or pinot and a auditory canal or me itis these and many of the parts that are to follow have been given the names because they resemble familiar objects a second the middle layer ear drum also called the tympanum consisting of the drum membrane already compared to a drum head and the drum cavity this is shut away from the outer ear by the drum like the outer ear the middle ear contains air it is the purpose of the eustachian tube to equalize the air pressure on both sides of the drum membrane to prevent its being injured by violent noises or changes in air pressure and now let's look at a still larger view of the middle ear with its three ear bones or articles and then see what happens when sound waves strike the drum membrane this bone consisting of a head then handle is called a hammer or stair up is attached by a movable ligament to an opening which is called the oval window if from any cause the drum membrane is forced inward its movement is transmitted to the state pays and the upper part of its foot plate swings in the interior as on a hinge repeated pushes make the plates swing in and out agitating the liquid which fills the inner ear and now let's see how sound waves coming from a ringing bell act upon the air mechanism here we see in slow motion how these sound waves by beating against the drum membrane are carried across the middle ear to the inner ear by the chain of articles the inner ear or labyrinth contains the minute but extraordinary mechanism which finally converts sound waves interne if the ear drums should be destroyed sound waves could still reach the inner ear through the surrounding bone and cause some sensation of hearing but destruction of the labyrinth itself causes complete deafness considered in connection with hearing our real interest is in this rounded portion with the two small openings and of course the part with which is united and which looks like the shell of  returning to our section of you we see that the rounded portion contains a hollow chamber lying between the middle layer and the snail a number of openings lead to adjoining parts just like doors do from a hallway so it is called the best  these openings in the vestibule lead to the semicircular canals actively related to the hearing mechanism are these two openings which is already been pointed out on the outside of the labyrinth and which allow sound waves to pass from the ear drum to the inner ear first of these openings is called the round window is covered by a very thin membrane the second the oval window there where i received sound impulses transmitted by the plate of the stay piece which covers it and the third opening amazing little instrument we were to slice through the middle of the cochlear and then turn the separated portion face upwards we would see inside a spiral shaped canal which circles around a central core of bone called the dialers this can is divided into an upper and lower portion by a membrane shaped like a spiral ramp this membrane is a highly complicated internal construction and when agitated by sound waves sends out nerve impulses these are conducted to the brain by nervous what  now let's look at a simple diagram of the cochlear and its action and this time let's take off the top here again bring we recognize the best to build with the oval window covered by the stirrup and directly below is window covered by its membrane and here is the third opening which leads directly into the inner channel of the cochlea this white line represents the all important spiral membrane which transforms sound waves into the sensation of hearing as we've seen before the space is filled with a liquid now here again we observe the action of sound waves upon the ear this is merely a simple picture of the complicated action th results when sound waves enter the inner ear by way of drum and ear bones the liquid when said into vibration causes wave like shakings of the spiral membrane the shakings in turn set up a nerve action which when carried to the brain results in the sensation of hearing the ear then is a very delicate and complicated mechanical device astonishingly sensitive in its ability to separate and to distinguish a vast medley of sounds it excels by far the most ingenious and delicate instruments ever devised by man