As they approached the foothills of the eastern chain or arm of the mountains, Paul took the throttle, and they steadily arose in order to clear the high pinnacles facing them, and finally, at a height of fifteen thousand feet--the greatest height they had yet attained--they went over them.  The airplane encountered several "air pockets" in this process, which might have been disastrous to them except for the stabilizing effect of the automatic-pilot.  As it was, the machine pitched rather roughly in surviving them.