Their perils had begun in earnest.  Should anything happen to cause them to be forced down, there was nothing but a vast basin of water miles deep to catch them, and there would not be one chance in a thousand that they would survive.  This, surely, was no place and no time for engines to fail or steering apparatus to go wrong.  Yet each flyer was ready for such a mishap--attested by the mute evidence of an inflated rubber tube about his waist.  Even Bob and Paul slumbered on the airy contrivances.