"For a long time I was unable to account for these eccentricities, and the problem was not rendered much clearer, although a startling suggestiveness was added to it, when, at length, I noticed that the periods of activity of the engine had a definite relation to the age of the moon. Then I discovered, with the aid of an almanac, that I could predict the hours when the engine would be busy. At the time of new moon it worked all day; at full moon, it was idle; between full moon and last quarter, it labored in the forenoon, the length of its working hours increasing as the quarter was approached; between last quarter and new moon, the hours of work lengthened, until, as I have said, at new moon they lasted all day; between new moon and first quarter, work began later and later in the forenoon as the quarter was approached, and between first quarter and full moon the laboring hours rapidly shortened, being confined to the latter part of the afternoon, until at full moon complete silence reigned in the mill." "Well! well!" I broke in, greatly astonished by Hall's singular recital, "you must have thought Dr. Syx was a cross between an alchemist and an astrologer." "Note this," said Hall, disregarding my interruption, "the hours when the engine worked were invariably the hours during which the moon was above the horizon!" "What did you infer from that?" "Of course, I inferred that the moon was directly concerned in the mystery; but how? That bothered me for a long time, but a little light broke into my mind when I picked up, on the mountain-side, a dead bird, whose scorched feathers were bronzed with artemisium, and sometime later another similar victim of a mysterious form of death. Then came the attack on the mine and its tragic finish. I have already told you what I observed on that occasion. But, instead of helping to clear up the mystery, it rather complicated it for a time. At length, however, I reasoned my way partly out of the difficulty. Certain things which I had noticed in the Syx mill convinced me that there was a part of the building whose existence no visitor suspected, and, putting one thing with another, I inferred that the roof must be open above that secret part of the structure, and that if I could get upon a sufficiently elevated place I could see something of what was hidden there. "At this point in the investigation I proposed to you the trip to the top of the Teton, the result of which you remember. I had calculated the angles with great care, and I felt certain that from the apex of the mountain I should be able to get a view into the concealed chamber, and into just that side of it which I wished particularly to inspect. You remember that I called your attention to a shining object underneath the circular opening in the roof. You could not make out what it was, but I saw enough to convince me that it was a gigantic parabolic mirror. I'll show you a smaller one of the same kind presently.