They had been flying thus for perhaps two hours, when Paul saw that for which he had been keenly watching for some time.  It was a faint black speck, like a tiny bird, against the blue of the heavens ahead of them. He continued to watch this silently, after calling his chum's attention to it, until, under an increase of speed, the Sky-Bird had drawn close enough for them to observe that it was what they suspected--an airplane.