"Around the sash in the big window the architect has inserted a row of glass bull's-eyes, a style of ornamentation suited to the semi-Oriental tastes of William H. Seward Square. I go up and examine them closely. They seem ordinary enough--but stop! The third from the bottom; it has a peculiar depth and clearness. It might very well be a lens--a burning-glass, to use the old-fashioned term. How close has the sun drawn to this particular bull's-eye? To-morrow I will take note. "March 20. At high noon the sun has reached within a hair's-breadth of the third bull's-eye from the bottom. To-morrow it will surely shine through my suspect, and if the latter be a true lens it will concentrate, for several minutes, a high degree of heat at the particular spot upon which its rays are focussed. That spot I have found, by experiment, to be one of a series of small bosses set in the pivot-base of the big chair. I applied the flame of a match and immediately the metal boss began to soften. I understand now. The boss is made of a fusible alloy that melts at a certain prearranged temperature; it is simply a variation of the common safety plug used in all the systems of mechanical protection against fire. At noon to-morrow, March 21st, the rays of the sun will be concentrated by the lens in the window-sash and will fall upon this boss of fusible metal. The plug will melt, releasing a spring, let us say, and a train of action will be set in motion. "The precise nature of that action I shall probably not discover. I incline to the belief that it is of an electrical nature. A connection is to be thereby established with one of the deadly currents that can be tapped for the asking here in New York. It may be objected that the men who died in the chair over there showed no external marks of death by electrical shock. But the autopsy, if it had been performed by Coroner Lunkhead, might have told a different story. Magnus is as good an electrician as he is a chemist, and he could easily rig up some kind of transformer reducing the power of the current just enough to paralyze the victim--death by a myriad of small shocks instead of one big one. Now it is plain why the spider will not come to spring his trap unless the sun shines on the 21st of March. If it doesn't, the play goes over to the next clear day, only that the curtain will rise a minute or so earlier in correspondence with the onward march of the sun-god, the executioner in the cast of our drama. Well, I have made my preparations to counter-check. To-morrow we shall see what we shall see. "March 21. I have still an hour before the expressman will come for the clock-case, and I must take the opportunity to finish my notes. The dead man sits opposite me at the table, but that does not matter. There is plenty of room for us both. "The day dawned clear and fine, and at ten o'clock the sun was shining brightly. He will come then.