"I hadn't tried to estimate it," said Terry. "You've got a tape of the noise," said Tony. "Could you time the interval between the sound when it left the water, and the splash when it fell back?" "Mmm. Yes," said Terry. He looked up. "Of course." "It would be interesting to do it," said Tony, semicasually. Then he added hastily, "I've read somewhere that whales have been clocked at pretty high speeds. If we can find out how long its leap lasted, we could know how fast it was going." Terry considered for a moment, and then got out the recorder. He played the tape for a moment, and skipped forward to later parts of the record until he came to the place where the unpleasant humming sound was loud, and finally reached the beginning of the rushing noise. That, in turn, had preceded the leap of the object photographed by the gun-cameras. Terry glanced at his watch when the rushing started. He timed the period of ascent of the noise, while it grew louder and louder and became a booming sound, which was at its loudest the instant before it ceased. At that moment the mysterious object had leaped out of the sea. The splash of its re-entry came long seconds later. Tony timed the leap. When the splash came he made his calculations absorbedly, while Terry switched off the recorder. "It would take the same amount of time going up as it does coming down," said Tony, scribbling numbers. "Since we know how fast things fall, when we know how long they fall we can tell how fast they were traveling when they landed, and therefore when they leaped." He multiplied and divided. "Sixty miles an hour, roughly," he pronounced. "The whale was going sixty miles an hour straight up when it left the water! What can swim that fast?" "That's your question," said Terry. "Here's one of mine. We heard it coming for five minutes ten seconds. How deep is the water where we were?" "About forty-five hundred fathoms." "If we assume that it came from the bottom, it must have been traveling at least sixty miles an hour when it broke surface," said Terry. "But can a whale swim sixty miles an hour?" "No," said Terry. Tony hesitated, opened his mouth, closed it, and went away. Terry returned to the changing of the submarine horn. Sound has its own tricks underwater. If you know something about them you can produce some remarkable results. A deliberately made underwater signal can be heard through an unbelievable number of thousands of miles of seawater. But, except through a yet untested fish-driving paddle, Terry had never heard of fish being herded by sound. Still, fish can be stunned or killed by concussions. They have been known to be made unconscious by the noise of a very near submarine bell. It wasn't unreasonable that a specific loud noise could make a barrier no fish would try to cross. But there were still some parts of last night's events that did not fit into any rational explanation. Davis came over to Terry.