But of all the events of that period the one which had, perhaps, most significance was the return of Hildegarde von Essen. Potter was being, had been, modified by a number of momentous happenings whose effects he was able himself to see. Hildegarde was to modify him without his perceiving it. And it may be asserted that her modification was the most profound, far-reaching of all. It is the intent of Nature that the life of man shall stretch over many years. A third of these years, say twenty-five, are used up in bringing him to man's stature and in equipping him with mental tools to carry on the trade of living. At the end of this period he stands balanced in the doorway, ready to step out into the jostle. It is usually at this moment that a woman intervenes. The most critical event of any man's career is the advent of some woman. This point may be argued and combated, but not successfully. It is critical because it is the major point of departure in his journey. The character of this woman touches every instant remaining in the man's life, either for good or ill. And it is all a matter of chance! Here Nature does not plan. One might almost accuse her of being sardonic. She shuts her eyes, shuffles together a multitude of young men and young women, themselves blindfolded, and then gives the word, "Choose your partners." Perhaps that is the fun Olympus gets out of godship. It may be the whole thing is some Olympian gamble. Upon this blind scramble depends the future of the race! The marvel of it is that so many grasp possible partners. Men are educated to choose a profession or business; they are educated to enter a drawing-room; they are educated to choose a hat or a cravat. But to choose a wife--that choice which is so paramount that one might almost say it is the one choosing of his life, is not a choice of educated reason, but is a blind snatch into a grab-bag. The worst of it is that he cannot refuse to grab. Nature has seen to that. For the perpetuation of the race she has given him sex, and sex may bless him or damn him, she cares little which, so long as she produces another generation. It forces him into the game. Potter had news of Hildegarde's return from Hildegarde in person. He was working in the old hangar--the one to which she had come looking like a fairy prince on the day of their disastrous flight. It was now his headquarters, enlarged to accommodate his needs. The building housed a reasonably complete machine-shop, drafting-room, a combination technical library, office, and study, as well as the rebuilt hydro-aeroplane for which it had been constructed originally. Here Potter worked, and here his world was content to leave him alone with his fad. Few visitors came, and these found themselves unwelcome, for Potter was busy. He was designing a motor that would be efficient to drive the battle-planes of his country to victory.