BLIND FLYING

Wairarapa Times-Age, 2 December 1941, Page 6

BLIND FLYING

BATS USE ECHO SYSTEM. WHAT INVESTIGATION SHOWED. Although bats have fair vision day or night, one of the strangest bat tales ever told concerns their ability at “blind flying,” disclosed by Robert Galambos and Donald R. Griffin, Harvard researchists, who gave joint reports before the American Association for the Advancement of Science in Philadelphia, states a writer in the “Christian Science Monitor.”

Only recently has an instrument been developed, the fathometer, which measures the time it takes for sound waves to travel from the bottom of a boat -to ocean or lake bed and return, and which translates this data automatically into depth readings so that a skippei’ can tell how deep the water is beneath him. Within the last year a similar device, called an “absolute altimeter” has been developed for aviation pilots. But, according to Mr Griffin and Mr Galambos, bats use a similar system. They found that flying bats are warned of obstacles in their path by emitting high-pitched sounds inaudible to the human ear, then listening for the echo. Bats are not blind, but so acute is their “supersonic” blind-flying system that they do not need to see, the Harvard biologists conclude. This accounts for their extraordinary ability to fly swiftly through pitch dark caves without once striking a wall or projection. Mammalogists have long suspected that bats emitted sounds inaudible to the human ear because they noticed that when handling these creatures the bats would cry out audibly for a while and then no sound could be heard, although the mouth would remain open. Detection was achieved with a thermionic device developed by Professor G. W. Pierce at the Cruft Physics Laboratory at Harvard. The sounds were found loudest at about 50,000 vibrations a second. Only very few human ears can detect sounds with more than 20,000 vibrations a second. The investigators had an ingenious method of proving their theory. They erected a barrier of vertical wires in a closed room and used the supersonic apparatus to record the cries. Most of the time the bats managed to miss the wires, but the percentage of hits was 36.5, which did not change even after the bats were blindfolded.

According to Mr Griffin, these researches should end the fears of persons who encounter bats in a dark room oi; atic and anticipate that the flying animal will strike them. Actually the bats will normally perceive and avoid the human intruder through sound echoes.