But the mere haphazard introduction of the Sigma ray into the room would not suit my purpose; my revenge would not be complete unless I could see it in operation. And so it was necessary to arrange some sort of clockwork mechanism to spring the trap. I confess to being somewhat grandiose in my conceptions, and accordingly I decided to press into my service no less an agency than the solar system itself. If you will go into the library of "Hildebrand Hundred" on any month of the year outside of June you will see that the direct rays of the sun never reach the upper part of the "Spy" window; consequently, the Sigma ray is not brought into being. But, as the summer solstice approaches, the sun continues to rise higher and higher in the heavens until, in the three or four days around the twenty-first of June, it has reached its ultimate altitude with reference to the zenith. For the few minutes immediately before or after high noon on any of the aforesaid days the sun is in such a position that its beams will pass through the purple bullseye lens that forms the third grape in the upper row of the largest cluster. And in passing through it will become decomposed into the Sigma ray, and will fall on the head of him who sits at the great desk, exercising the authority of his lordship over "Hildebrand Hundred." This is all plain and straightforward, I think. It is unfortunately true that any innocent person who chances to be occupying the seat perilous at the fateful moment will have to bear the weight of the vengeance intended for the guilty. But that risk is really remote, since the great desk and chair are the natural appanage of the Master of the "Hundred"; it will not be usual for anyone else to trespass upon that prerogative. And what more natural procedure than that the Master of the "Hundred," after a tour of his hay fields on a hot June day, should go to the cool of his library and finish up his office business at his desk? True, there are other contingencies. The Master may come to the room and yet choose to sit elsewhere. Or he may forestall the hammer stroke of doom through the chance of rising from his chair to select a book from a distant shelf; or, finding his match-safe empty, he may go over to the chimney-breast on the hunt for a vesta. Or again, he may be away from home during the three or four days of fate, or lying ill in an upstairs room. Finally, should the period of danger be cloudy and overcast the sun may not shine at all, and the whole business must go over for another year. But my patience is very long; I have learned how to wait.