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For those who begrudge an hour wasted at an airport or while in transit, the paper-bounds have been a revelation. One can read classics conveniently. Griffin, Professor of Zoology at Harvard, writes lucidly and excitingly of the uses of sounds by animals and men to locate food, enemies, and obstacles, a field where physics and physiology merge, a field of necessity to the military forces, to peacetime employment, and to the blind for whom it may mean "sound vision."
Gorrell RL. Echoes of Bats and Men. Arch Intern Med. 1963;111(6):843. doi:10.1001/archinte.1963.03620300163033