A room painted black, strung with wires, some bats turned loose in it, and doors and windows closed to darken it totally--this might seem childish dabbling when thought of in connection with the modern science of aviation. Yet it was a test tried out with a very real purpose. Outside of that room men waited at ear-phones connected electrically with those wires so that the least flutter of a bat's wing against a wire would be indicated. The bats flew madly round and round the room, but never so much as touched one of the many wires. From this experiment scientists contended that bats flying in the air put out some sound and get an echo from that sound when it vibrates near an object. Not so far and foolish a leap from bats to aviation after all! For if a human flyer of the air could devise a ship that put out a sound and got an echo when it approached an object, it would help solve the problem of landing in the dark and of flying in fogs.