Up he went in great sweeping spirals, ever mounting higher and higher, the engine of the Wind Bird working beautifully. The altimeter told him he was at the height of seventeen thousand feet,--now he had reached eighteen, nineteen, twenty thousand! His ship was still climbing, acting beautifully. But he, Hal Dane, was not acting right. In the face of triumph, his whole sky world went suddenly gray and dreary, he felt a queer lassitude, and a slowing up of faculties.