I do not wish to labour the details of that afternoon. I may say that already I had a very distinct and curious impression of them, namely, that they _were_ details, isolated and without continuity; but I will come to that presently. We sat rather a long time over tea, and Derry talked. The only subject he seemed to avoid was that of his work. Otherwise he was alert, keen, dead "on the spot." On athletics he was extraordinarily illuminating. Granted that as an engine his body was pretty near perfection; it was on the "fundamental brainwork" of the subject that he laid the greatest stress. The modesty of the demonstrations which he made on the verandah before our eyes was altogether charming; he was as simple and earnest with us as he had been with the boys. For such-and-such a performance (he showed) your balance _must_ be thus and thus; for swiftness, a certain speed of movement _must_ be the perfectly-synchronised sum-total of half a dozen different speeds. I am no very remarkable athlete myself; I have always supposed that I lacked some special gift; but Derry spoke almost as if, by the mere taking of thought, he could add a cubit to his leap or plunge. He took his sport and his writing in very much the same way. You "just helped nature all you could." Then he was back on the subject of the incinerator again. Shortly after that it was an oak that ought to be lightened on one side unless I wanted to have a hole torn in the bank of my pond. Then, dinner over, he began to fidget. This was at a little after eight o'clock. At twenty past he rose abruptly. "It's that bathe I suppose," he yawned. "If you don't mind I think I'll turn in. You said I might, you know----" "I'll show you up," I said. "Don't trouble," he replied, Julia's hand in his. But I wanted to make sure that the tea-caddy was where I had told Mrs Moxon to put it. II On the night when he had half scared me out of my wits with that horrible demonstration with the electric torch on the edge of the bamboo table, he had been careful to explain that he was putting the question in its most elementary form. There were (he had said) other factors, and more important ones. One of these had already occurred to me. Stated as simply as possible, it was this: As he had held the torch that night, with that notch that "had got to be thirty-three" in the middle of the illuminated edge, about six inches on either side of the notch had come within the lamp's beam. "Keep your eye on that edge and never mind the other dimensions," he had said, and he had proceeded to manipulate the lamp. _But how had he determined the distance at which the lamp must be held from the table's edge?_