The wind blew. The waves raced. The Esperance's bow lifted and dipped. The noise from the loudspeaker system—the noise from the sea—decreased even more. One could hear the squeakings and chitterings of fish again. But they were very much fainter. Presently the humming was no louder than before the strange apparition. By that time the fish-sound had died away altogether. The nearer normal noises remained. The hum was receding. Downward.
Davis came to Terry, where he stood by the recording instrument.
"The fish have gone," he said in a flat voice, "they've gone away. They didn't scatter. We'd have seen it. Do you realize where they went?"
Terry nodded.
"Straight down. Do you want to hear an impossible explanation?"
"I've thought of several," said Davis.
Doug came and picked up the gun-cameras that Terry and Deirdre had used and went away with them.
"There's a kind of sound," said Terry, "that fish don't like. They won't go where it is. They try to get away from it."
Deirdre said quietly, "I would too, if I were swimming."
"Sound," said Terry, "in water as in air, can be reflected and directed, just as light can be. A megaphone turns out one's voice in a cone of noise, like a reflector on a light. It should be possible to project it. One can project a hollow cone of light. Why not a hollow cone of sound, in water?"