very blind and helpless when deprived of them. When you asked me to believe that she walked along a narrow strip of grass without once making a false step, I remarked, as you may remember, that it was a noteworthy performance. In my mind I set it down as an impossible performance, save in the unlikely case that she had a second pair of glasses. I was forced, therefore, to seriously consider the hypothesis that she had remained within the house. On perceiving the similarity of the two corridors, it became clear that she might very easily have made such a mistake, and, in that case, it was evident that she must have entered the Professor's room. I was keenly on the alert, therefore, for whatever would bear out this supposition, and I examined the room narrowly for anything in the shape of a hiding-place. The carpet seemed continuous and firmly nailed, so I dismissed the idea of a trap-door. There might well be a recess behind the books. As you are aware, such devices are common in old libraries. I observed that books were piled on the floor at all other points, but that one bookcase was left clear. This, then, might be the door. I could see no marks to guide me, but the carpet was of a dun colour, which lends itself very well to examination. I therefore smoked a great number of those excellent cigarettes, and I dropped the ash all over the space in front of the suspected bookcase. It was a simple trick, but exceedingly effective. I then went down-stairs, and I ascertained, in your presence, Watson, without your perceiving the drift of my remarks, that Professor Coram's consumption of food had increased—as one would expect when he is supplying a second person. We then ascended to the room again, when, by upsetting the cigarette-box, I obtained a very excellent view of the floor, and was able to see quite clearly, from the traces upon the cigarette ash, that
