Ultrasounds (1949)

[Music] [Music] a what is sound you might say sound is anything you hear but there are also sounds that you can't hear this however you can hear the surface of the gang vibrates rapidly this causes a disturbance in the air around the gang the vibrating surface of the gang sends out vibrating waves of air just as a pebble dropped into a pond sends out little waves or ripples over the surface of the water we call these vibrations of the air sound waves when they strike our ear they cause the eardrum to vibrate at the same rate and we recognize the sound we strike a smaller gang sound waves it sends out make the eardrum vibrate more rapidly this is a different sound a higher pitch the more rapid the vibration the higher the pitch now that was a high pitch sound disagreeable to hear when the rate of vibration per second becomes too high when it exceeds 7,000 vibrations per second the human ear can no longer register it we don't hear the sound but it still goes out through the air and we can prove it to you we can let you actually see sound that you can't hear we can do this by means of an electrical device it's the brunch tube that changes sound waves into electrical impulses well that in itself should be nothing strange to you it's the basis of radio and television broadcasting but the branch tube makes sound visible to you now you can both see and hear this sound but as the rate of vibration rises above the limit of reception of the human ear the pitch gets higher and we can no longer hear the sound though we can see it as the pitch Rises the tops of those circly lines are closer together and now as the tops of the circles grow wider apart the pitch drops and we can hear the sound again as well as see it but how can we produce super sound waves vibrations of air so rapid that the human Air does not register them well one way is to place a quartz slab between two electrodes so that it vibrates as fast as the electric current changes directions we use a high-speed alternating current and the vibrating quartz bar then sends out Super Sound wavs now we'll turn on the electricity now this sends out super sound waves that we can direct through the air the way you direct light waves from a flashlight or a search light and we can also bring the sound waves to a focus just the way we can bring light rays to a focus you see how we Bend those light rays we can do that with sound waves too of course ordinary sound goes around corners this Noonday whistle for instance turns a corner and tells this Workman that it's time for lunch here's a proof that we can focus sound waves as we do light waves this is a focusing device a concave metal mirror that we're putting in a tank of Water Sound travels through water five times as fast as it does through air of course we can't see the disturbances in the air caused by sound waves but we can see them in water and photograph them too with a special lighting device you see if you wave a stick in the air you don't notice the airwaves you dist but if you wave a stick in the water you can actually see the disturbance you create in the water well that's the principle of this experiment we can see the Disturbed particles of water where the sound waves make them vibrate now here we are we're focusing the sound waves now those bright streaks are the water particles that are being moved by Super Sound and you can also see they're being focused by that metal focusing mirror now these sound waves have energy or they wouldn't disturb the air or the water or anything else now we take out the mirror and put in a a flat block of plexiglass doesn't Focus anything and we'll turn the sound waves in on that and see what happens now the sound waves strike it and you can see they just spread in all directions you could get the same effect turning a stream of water against a wall you see the water particles are Disturbed and even after you turn on sound the the particles take a little time to come to rest now I said sound waves have energy and here's further proof of it this is a question of just dropping some Earth into the tank and you can see it would fall naturally if there were no sound waves blowing it away so to speak of course if you turn sound waves underneath this uh cup of water it will make it Disturbed just as though it were bubbling you can do the same thing with oil now here's a way of actually measuring the energy of sound in water this is a delicate device with a wide thin plate in the water below and a swinging indicator to show any movement of the plate now we turn on the sound and it strikes the plate and drives it forward the indicator above registers the force of the sound all these properties of sound can be put to good use as in navigating ships for instance let's watch this fall and see what he has to do with sound [Music] well it's an old boyish trick we yodel or yell and a distant Cliff or Hill sends back an echo we know how fast sound travels about a mile and 5 Seconds in air if we time an echo we know how far off the object is it sends back the echo while in navigation a ship can send a sound wve to the Bottom of the Sea it bounces back the Navigator takes the time of this traveling sound and knows exactly how far beneath the keil of a ship the floor of the ocean may be now we can use ultrasound for testing the quality of metals too a faulty bar will not transmit or reflect super sound waves in exactly the same way as a perfect metal bar where there's a difference in what you might call the sound effects there is a difference in the metal itself a fault well a worker marks a spot where he gets this sound reaction or you might call it an unsound reaction these are the faults in the metal that must be repaired or removed another thing we can do with Super Sound is to mix oil and water now I'm pretty sure you can't mix oil and water when you pour them together the oil immediately comes to the top we even say pouring oil on Troubled Waters but if we turn on the Super Sound the rapidity of the vibration will really mix oil and water into what you could call a permanent mix and sometimes we need it we want it and with Super Sound we can do this on a commercial basis but the latest use to which Super Sound is being put is as a healing device in European clinics now we know that massage is beneficial to some patients suffering from various afflictions well Super Sound is something like a super massage without using the hands now here's this chair for instance we fill the whole seating section with water and and turn on the Super Sound from below the Super Sound Vibrations are transmitted through the water to the body of the patient sitting in the chair plus we can also use Super Sound Airwaves themselves in a smaller device like this and if you hold your hand over it the vibrations will make that water in your hand jiggle well as this nurse gives another patient a treatment of Super Sound I think we can agree on a few things one is that what we hear is sound the other is there are sounds that we can't hear but we can see them and feel them oh [Applause] [Music]