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  • Osmania University librarqCall No 6"3^ - A Accession No.



    This book should be returned on or before the date last marked^below








    Introduction 7

    Chapter 1. THE WORLD OF SOUNDS ... 9First, About Audible Sounds 11

    Competing Sounds 13Limits of Audibility 17

    Supersonic Sounds 18


    Many Years Ago 21When France Was in Danger . ... 23Sound and Light 24Wonderful Crystals 27To Nature's Aid 30How to Make a Supersonic Generator ... 33How to "Hear" Inaudible Sounds .... 37Why Do Transformers Hum? 39A Reliable Scout . . f 41A Mechanical Watchman 47The Supersonic Echo Sounder 49Supersonic Waves Become Visible .... 52


    The Riddle of Bats 59

  • PageAlong the Path /Pointed Out by Nature . . 62Action of Supersonics on Simplest Living*

    Creatures 64What Happened to the Fish? 69

    Chapter 4. SOUND AND CHEMISTRY ... 73The First Steps 73Electrical Charges and Bubbles 75Giant Molecules 79

    Duality of the Properties of Inaudible Sounds 81A Mysterious Glow 83Supersonics Substitutes Time 85

    Chapter 5. ONE OF MAN'S HELPERS ... 87Sounds that Crush 87Supersonics Saves Human Lives .... 91Science and Practice 92

    Washing Woollens with Supersonics ... 94The Supersonic Soldering Iron 95

    Purifying the Air with Supersonics .... 99A New Supersonic Source 102Supersonics Helps to Intensify Production . 104

    Fluidization 107

    Chapter 6. SUPERSONIC CON FROL . . . 109

    Sound as Inspector 109

    Through Sounding HO

    Reflecting Defectoscope 112

    A Mechanical Memory 119

    Overcoming Obstacles 120

    Supersonic Diagnosis 123

    Saving Human Lives 125

    How Supersonics Helps to Investigate theStructure of the Earth 129

  • PageSupersonics Controls Chemical Change . 130How to Determine the Elastic Properties of

    Substances 133

    Supersonic Flow Meter 136A Thickness Gauge 138

    Chapter 7. THE SUPERSONIC MICROSCOPE 141Supersonic Optics 141

    Design of the Supersonic Microscope . . 144A New Design 147Practical Application of the Supersonic

    Microscope ...... 14r)


    This booklet deals with the achievements of a new, rap-idly developing branch of science.Discovered very early in the 20th century, inaudi-

    ble sounds immediately drew the attention of researchworkers in various branches of science and engineering.Several thousand scientific papers have already been pub-lished on the properties of inaudible sounds and their

    practical application.

    Supersonic vibrations were first used for practical pur-poses in France. Especially noteworthy in this connectionare the works of Academician Langevin.

    Soviet scientists have also played a prominent part in

    developing the science of inaudible sounds and the meth-ods of their practical application.

    Wtatching the development of science is like reading a

    thrilling novel. We can all recall reading a book we couldnot tear ourselves away from. How breathlessly we fol-lowed the fate of the hero, how 'glad we were when he wassuccessful, how sorry when fate was cruel to him! Re*member how we yearned to know what awaited him in thefuture, how we tried to guess which of his plans would bosuccessful and which of them would remain unrealized!

    It is the same when you watch the development ofscience; you iare always trying to catch a glimpse of itstomorrow.

  • In this book we shall tell of various discoveries in thefield of inaudible sounds. Some of the applications of in-audible sounds may not justify our expectations in the fu-ture; it is quite possible that we shall make mistakes inour explanations of .the action of supersonics, and shallhave to begin our work anew Then we shall recall thewords of Karl Marx that f 'there is no royal road to science,and only those who do not dread the fatiguing climb ofits steep paths have a chance of gaining its luminoussummits."

    If any of our readers should become interested enoughin the applications of inaudible sounds to try his hand inthis field, he will find the doors wide open before him intothe boundless and fascinating world of scientific discov-


    The study of inaudible sounds is at present an unlimit-ed field of activity for investigators of nature, and it opensup immense opportunities for the application of the crea-tive power of man.



    world we live in is full of sounds. Devoid of sounds,the wodd would be incomparably poorer. Our conceptionof a forest is inseparably connected with the singing ofthe birds, with the rustling of the trees; that of a meadow

    with the chirring of the grasshoppers; of the sea with

    the roar of the waves 'and the crash of the breakers; of a

    city with the characteristic diversity of sounds known as"city noise/' a sort of symphony combining the distanthooting of locomotives, the ding-a-ling of trams, scrapsof conversation or music, and the muffled rumble of numer-ous factories and plants.Very long ago man learned to find pleasant combina-

    tions of sounds, to make up musical melodies. Musicis by right considered one of the earliest arts. The magicfcharin oJ musical melodies has given rise to many poetic

  • legends. Our ancestors even used to attribute supernaturalproperties to music. They held that music could tame wildbeasts, move mountains 'from their seats, hold back floodsof water, calm down the raging elements.Man learned to make musical instruments very early. On

    Egyptian pictographs we find images of musicians playingflutes and harps. The science of sound, or, as we call it to-

    day, acoustics, was founded by the ancients. The first ex-

    periments in acoustics of which any records have comedown to us are those of the Greek philosopher and scien-tist Pythagoras, who lived twenty-five hundred years ago.

    Since that time man has put great efforts into the studyof the nature and properties of sound. And gradually, bythe end of the 19th century scientists came to beftevethat they knew practically everything there was to knowabout sound. It seemed that all that was left in acousticswas to describe already known phenomena, using improvedinstruments, to refine earlier determined values, butthat nothing new would ever be discovered in this field.

    But that was a mistake.Our knowledge of the surrounding world keeps contin-

    uously expanding and deepening, "and while yesterday/'Lenin teaches us, "the profundity of this knowledge didnot go beyond the atom, and today does not go beyondthe electron and ether, dialectical materialism insists onthe temporary, relative, approximate character of all thesemilestones in the knowledge of nature gained by the

    progressing science of man. The electron is as inexhausti-ble as the atom, nature is infinite


    It turned out that the world of sounds also held secrets,which man had not yet guessed to exist. At the very timescientists were about to yield to the idea that everythingin acoustics was already known, a new fascinating chap-ter was opened in science, the door was thrown wide open


  • into a hitherto unknown kingdom of nature, the kingdomof inaudible sounds.

    This discovery was one of great importance. Having es-tablished the properties and peculiarities of inaudiblesounds, mam began to use them successfully as a means of

    delving further into the secrets of nature. They 'became the

    helpers 0$ man.


    It is impossible to understand the properties of super-sonic sounds without an acquaintance with ordinary au-


    dible sounds. Therefore, we shall tell the reader very brief-

    ly what is known about the nature and properties of th4ordinary sounds that we can hear.

    Let us fix our attention on the sounds th?l come to usthe moment we wake up. There, for instance, goes a fac-tory whistle.

    What happened when the whistle b 1The operator opened a valve, and ..pressed air rushed

    forcibly out into the atmosphere .id expanded, takingup a much greater volume. Unde> the impact the mole-cules of the air also shifted. Biu molecules cannot travelfar. Moving forward abruptly, [hey mix with the moleculesin the air layers in front of them and exert^ pressure onthem. Thus, for a very shoit moment the number of mole-cules in the adjacent layers becomes much greaterthan before. This means that for an instant the pressurein those air layers increases, and the air becomesdenser. I

    The whistle sends forth an intermittent stream of

    compressed air, and these molecular impacts occur ftianytimes each second, + ,

  • At the instants the air stream is interrupted the shift-

    ing of the molecules leads to their momentary deficiencyin the layer next to the compressed one. Therefore, nextto the high pressure layer there arises a rarefied layer,where the pressure is low. As long as the whistle keepsblowing .the compressed and rarefied layers keep runningin all directions.

    When they fall on the human ear these alternate com-pressions and rarefactions give rise to the sensation ofsound.

    Thus, what we call sound is a sequence of rapidly alter-

    nating compressions and rarefactions of the air.The individual particles of air, however, -do not move

    together with the propagated sound. They only osci