Whitney, sitting astride an ordinary wooden chair, followed the detective's movements with sardonic amusement, which now and then found vent in a grim smile. Whitney's expression was not lost upon Miller, who, finding him a more interesting study than Mitchell, watched him intently while appearing to be deeply engaged in examining an elevator model. "Isn't this the design copied in building your elevator, Mr. Whitney?" he asked. "Yes; that is the model I made when the elevator was built. It was one of the first installed in a private residence in Washington." "It is somewhat different from others that I have seen," commented the detective, replacing a bottle carefully on a shelf. "The cage is so very shallow in depth and so long in width." "I had to cut my coat according to my cloth," curtly. "This house is very old and the outer walls are of unusual thickness, also the inner ones, which accounts for the peculiar shape of the elevator. The brick shaft had to be built to conform to the walls and staircase. I also invented that safety air brake catch," he added, as Miller ran the elevator to the top of the shaft and released the cage with a sudden jerk. The elevator slipped down a flight, then automatically adjusted itself and stopped. "A clever idea," said Miller admiringly. "When I first used your elevator, Mr. Whitney, I was struck by its unexpected capacity to hold six people. Its shallowness is deceptive." "That's so." Whitney stared at the clock suggestively. "Kathleen, as a child, used to slip in unseen, and as the majority of the people enter the elevator facing the floor button plate with their backs to where she stood, she gave her governesses many scares." The detective stopped to examine the elevator model carefully, and pressed the button marked "Attic." "Persons entering the elevator instinctively pull to the inner door with their left hand and push the floor button with the right, and they would be standing with their backs to where Spencer lay," he said. "And anyone could have started the elevator without knowing of his presence," put in Miller softly, and the detective nodded assent. "You have no floor indicator connected with the elevator, Mr. Whitney," commented Mitchell thoughtfully. "No." Whitney rose abruptly. "Finished your search?" Not waiting for a reply he prepared to leave, and a covert sneer crossed his lips as he asked, "Found anything criminal?" "Only these bottles," indicating the shelves near the laboratory. "There's enough poison here to kill a regiment." "And only for use in photography," Whitney busied himself in adjusting shades which the detective had raised or lowered the better to see the room. "Rather a commentary on the laws governing the sale of poisons, Mitchell; can't buy them at a druggist's, but any man, woman, or child can go into a photographic supply store and buy any quantity of deadly poison and no questions asked."