51. Catching Up With Nature




Short Stories of Science and Invention A Collection of Radio Talks by Charles F. Kettering INDEX		*51.* *Catching Up With Nature* Using the most modern sound recording devices the men found that while in flight the bat emits a sound which has a frequency of vibration reaching a maximum of about 80,000 cycles - or, in musical terms, about 8½ octaves above middle "c." We call these sounds "supersonic" because their pitch is so high they cannot be heard by the human ear. Our range of hearing is somewhat greater than the highest note produced by instruments of the orchestra. The harmonics on the E string of the violin are about 10,000 cycles per second. Apparently, the bat while in flight sends out these inaudible sounds in short squeaks which strike the obstacle he is approaching and are reflected back and are picked up by his sensitive ears in time for him to steer clear of the object. This method of sound reflection has been used for many years to determine the depths of the ocean and the pilots of boats in Alaskan waters often use the echo of their boat whistles to determine if they are getting too near the cliffs when travelling in dense fog. Many other applications of this system are in daily use in laboratories for determining faults in materials and undoubtedly after the war it will be applied in many other ways. We feel proud of our recently developed sound echo devices even though the bat has been using it in the dark for thousands of years. We marvel at the automatic flying instrumentation of planes but every year flocks of birds go from their southern homes to their northern ones and return to precisely the same location with only their natural instrumentation.