_Zip!_ went a zigzagging livid streak across their range of vision.  It seemed to be running straight for them, and instinctively they dodged--all but Tom and John.  These old veterans continued to gaze coolly straight ahead as though nothing had happened.  _Crash-h!_ went a clap of thunder.  It seemed as if the whole heavens were being turned topsy-turvy.  Even the airplane, usually so steady, heaved and rode like a rocking-horse.