About noon one stifling hot day in August, rather more than thirty years ago, Robert Redblake Casson, senior partner of the firm of Casson, Hunter & Co., ivory merchants, of Old Queen Street, London, walked into the Fox and Greyhound Inn, Coalbrookdale, and ordered luncheon. While he was eating--there was no one else in the dining-room at the time--his eyes wandered to a large oil-painting hanging on the wall facing him. It represented a stream spanned by seven large stepping-stones. In the background of the picture, and leading to the bank of the stream, was a broad and very white pathway, bordered on either side by a thickly planted row of lofty pines. The artist, Casson thought, had depicted this scene with a more than ordinary touch of realism. The trees were no mere paint-and-canvas duds, but things of life--things that stood out prominently, each with an individuality of its own. He could almost see them move, see the rustling of their foliage and hear the creaking of their gently swaying bodies. Their shadows, too, were no empty, meaningless daubs, such as one too often sees in pictures, but counterparts, living, breathing counterparts, that, while conveying a sense of the physical, conveyed also a suggestion of the inexplicable. As to the water in the stream which rippled and babbled as it flowed, Casson could feel the speed and gauge the shallowness of it everywhere, saving round the centre stepping-stone, where it was green, and seemed to possess the stillness that great depths alone can generate. There was sunlight everywhere on the surface of the water, and here and there it shone and sparkled with all the brilliant lustre of the goldfishes' scales; but despite this animation, a sense of utter loneliness, a feeling of intense isolation, seemed to permeate the whole thing, and Casson, as he gazed, felt both chilled and depressed. He was still looking at the picture, and wondering what there could be in it to cause such a sensation of chilliness, when something made him glance at the stepping-stones, and, to his utter amazement, he saw the centre one suddenly begin to oscillate. Thinking it must be some kind of optical illusion, Casson rubbed his eyes and looked again, but the stone was still shaking, and he fancied he could discern the shadowy and indistinct outline of something or someone standing on it, swaying violently to and fro. The phenomenon lasted some seconds, and then very abruptly ceased.