The discovery of radar, the sending out of electromagnetic waves and judging the obstacles ahead by the returning echo, made some investigators wonder if this was not the system employed by bats. A series of experiments was conducted, and some fascinating things were discovered. First of all, some bats were blindfolded（ 蒙住眼睛） with tiny pieces of wax over their eyes, and as usual they had no difficulty in flying to and from without, hitting anything. Then it was found that if they were blindfolded and their ears were covered they were no longer able to avoid collisions（碰撞） , and, in fact, did not seem at all keen on flying in the first place. If only one ear was covered they could fly with only moderate success, and would frequently hit objects. This showed that bats could get information about the obstacles ahead by means of sound waves reflected from them. Then the investigators covered the noses and mouths of their bats, but left the ears uncovered, and again the bats were unable to fly without collision. This proved that the nose, ears, and mouth all played some part in the bat’s radar system. Eventually, by the use of extremely delicate instruments, the facts were discovered. As the bat flies along, it sends out continuous succession of supersonic（超声的） squeaks（尖叫声） , far too high for the human ear to pick up.

They give out, in fact, about thirty squeaks a second. The echoes from these squeaks, bouncing off the obstacles ahead, return to the bat’s ears and, in some species, to the curious fleshy ridges round the creature’s nose, and the bat can thus tell what lies ahead, and how far away it is. It is, intact, in every detail the principle of radar.