The changes were made even as he spoke; the propeller's hum grew into a mild roar through the cabin walls, and the Sky-Bird leaped away over the ground, gaining momentum at every yard.  To the surprise of even two such veteran flyers as John Ross and Tom Meeks, the airplane had gone less than fifty yards when she began to rise as gracefully as a swallow in response to her up-turned ailerons and elevators.  In less than ten seconds she was well up over the fair-grounds, and the roofs of all the buildings in the neighborhood were seen below them.