He heard gruntings and chirpings and rustlings. Fish made those noises—not all fish, but certain species. These shrill, squeaking noises were the protests of frightened porpoises. But under and through all other sounds, a steady, unvarying hum could be easily detected. Terry had never heard anything quite like it. Its pitch was the same as that of a sixty-cycle frequency, but its tone quality was somehow sardonic and snarling. The word that came into Terry's mind was "nasty." Yes, it was a nasty sound. One didn't like it. One would want to get away from it. In the air the same unpleasant sensation is produced by noises that make one's flesh crawl.
Terry straightened up from where the recorder played upon the wet deck. Davis and Deirdre had come to listen, in the strange darkness under the sails of the Esperance.
"I've got a sort of hunch," said Terry slowly. "Let's sail across the bright patch. I'll record the sea noises all the way. I've a feeling that that hum means something."
"It's not what you'd call an ordinary sound," said Davis.
He raised his voice. One of the crew-cuts was at the schooner's wheel. He spun it. The sails filled, and the rattling of flapping canvas died away. The Esperance gathered way and moved swiftly from the glittering circle, came about, and sailed again toward the shining area. She got closer and closer to the boundary.
The recorder continued to give out the confused and frightened noises of the sea creatures, but under and through their sounds there remained the nasty and sardonic hum. It grew louder and more unpleasant—much louder in proportion to the fish sounds. At the very boundary of the bright space it was loudest of all.
But as the yacht went on, the hum dimmed. At the very center of the circle where the glitterings were brightest, the humming sound was overwhelmed by the submarine tumult of senseless fish voices. Terry dipped his hand here. The tingling was almost tolerable, but not quite.
Davis hauled more buckets of water to the deck. In two of them he found some fish, so dense was the finny multitude. Then the yacht neared the farthest limit of the bright circle. The hum from the recording instrument grew progressively louder. Again, at the very edge of the shining water, it was loudest.
The Esperance sailed across the live boundary and into the dark sea. As the boat went on, the sound dimmed....
"Definitely loudest," said Terry absorbedly, "at the edge of the circle of fish. At the line the fish couldn't cross to escape. It is if there were an electric fence in the sea. It felt like that, too. But there isn't any fence."