They now had just four hours in which to reach their goal.  That meant they must travel at an average rate of better than 160 miles an hour. Since they had gone considerably faster than this when the occasion had warranted it in the past, they felt no anxieties now.  John, who was at the throttle, opened the Sky-Bird up to 165, and at this gait they skimmed swiftly along over the blue-green waters of the big Pacific.