Oliver Green was a very young professor, but a very old young man. He had passed from science as the hobby of a schoolboy to science as the ambition of a middle-aged man without any intermediate holiday of youth. Moreover, his monomania had been fixed and frozen by success; at least by a considerable success for a man of his years. He was already a fellow of the chief learned societies connected with his subject, when there grew up in his mind the grand, universal, all-sufficing Theory which had come to fill the whole of his life as the daylight fills the day. If we attempted the exposition of that theory here, it is doubtful whether the result would resemble daylight. Professor Green was always ready to prove it; but if we were to set out the proof in this place, the next four or five pages would be covered with closely printed columns of figures brightened here and there by geometrical designs, such as seldom form part of the text of a romantic story. Suffice it to say that the theory had something to do with Relativity and the reversal of the relations between the stationary and the moving object. Pierce, the aviator, who had passed much of his time on moving objects not without the occasional anticipation of bumping into stationary objects, talked to Green a little on the subject. Being interested in scientific aviation, he was nearer to the abstract sciences than were his friends, Crane with his hobby of folklore or Hood with his love of classic literature or Wilding White with his reading of the mystics. But the young aviator frankly admitted that Professor Green soared high into the heavens of the Higher Mathematics, far beyond the flight of his little aeroplane.