They devoted their attention now to the six planes. They were coming up in battle formation. They were in plain view and through the telescopes it could be seen that each was armed with bombs of some kind. Useless against the invisible space ship as matters now stood; but what would those bombs do to the inner globe? It still lacked several hours of the time allowed in the ultimatum to Jeter and Eyer of Sitsumi and the Three, when the six planes leveled off within a couple of miles of the space ship. They knew about where the stratosphere had swallowed up Jeter and Eyer. Now they were casting about for a sign, like bloodhounds seeking the spoor of an enemy. Jeter and Eyer held their breaths as they watched. Now and again they stole glances at Sitsumi and the Three, who were watching the six planes with the intensity of eagles preparing to dive. Naka stepped up close to Jeter. "When the time comes," he said menacingly, "and it appears that we may be in difficulties with the fools who think to thwart Sitsumi and the Three and rescue you, it shall give me great pleasure to destroy you with your own automatic." "Pleasant fellow," said Eyer. "Shall I smash him, Lucian?" Jeter shook his head. "Our friends out there will look after that, Tema," he said in a natural tone of voice. "I'll bet you two to one they get this ship within an hour. Not that a bet will mean anything, as they'll get us, too!" "Your friends," said Naka, "will be destroyed. They will not even be given the opportunity you were given. Sitsumi and the Three will waste but little time on them!" "What," said Jeter calmly "is Sitsumi's hurry? Why is he scared?" "Scared?" Naka seemed on the point of hitting Jeter for the blasphemy. "Scared? He fears nothing. We'll down your friends long before their motors--" Sitsumi suddenly turned and looked at Naka. The look in Sitsumi's eyes was murderous, Naka went dead white. "I think your master believes you talk too much, Naka," said Jeter, but Jeter's eyes were gleaming, too. As soon as Sitsumi had turned back to his station Jeter's lips began to move. "See?" he said. "It isn't their machine guns these people fear. It isn't their bombs--it's their motors! I wonder why...." * * * * * By now the six planes were flying abreast, in battle formation, almost above the space ship, at perhaps a thousand feet greater elevation. A strange humming sound was traveling through the space ship. The whole inner globe was vibrating, shaking--and vibration was a menace to glass or crystal! "We've got the answer!" said Jeter. "The outer rind, while capable of being softened--in sections at least, with safety--for special reasons, such as happened when we were 'swallowed,' can be hardened to the point of disruption. It can be shattered, Tema, by vibration! That's why the space ship keeps far above the roar of cities! The humming of countless automobile engines might shatter the rind! God, I hope this is the answer!"