When the mighty caisson had been warped and nudged dead into position over the desired spot, water was admitted. With a gurgling and hissing the hulk sank slowly into the sea. At last a slight jolt, which quivered through the mass, signified that the structure was resting on the bottom. The engineers gave a sigh of relief, but the next instant changed it to a cry of dismay. The caisson began to heel over to one side. Was it going to capsize? That was the absorbing fear. It canted more and more, until at last it had a list of 12 degrees. _It had not sunk vertically!_ There was less than 16 inches of water between the sea-level and the rim when the caisson first jarred against the sand, and if it careened over too far the water certainly would rush in, roll the whole tub over, and tumble it hither and thither over the sea-bed. The engineers watched that caisson as closely as a cat watches a mouse-hole. Presently it eased up, and then, as the tide rose some six hours later, it began to right itself. The engineers were relieved once more. The danger was over. But their self-satisfaction was soon upset as the tide began to ebb, because again the cylinder gradually fell over on its side. The cause of this strange behaviour flashed upon them. The surface of the sandbank was not level! The mass in sinking had touched bottom on the highest point of the shoal, and was trying to find its own level. Without any further delay, the engineers decided upon an ingenious means of correcting this erratic and dangerous action. The tugs were despatched hurriedly to Lewes to bring out cargoes of broken stone, which had been delivered for the preparation of the concrete. While the steamers pursued their errand, the engineers fashioned large pockets on the elevated section of the structure, into which the stone upon its arrival was placed. Gradually but surely the caisson not only was corrected, but the weighted end was induced to settle into the sand, until the opposite free edge in its turn was resting upon the shoal. In this manner all danger of further canting now was removed. As the rim had been brought perilously near the water-level, and there was a possibility of flooding from a rough sea, the walls of the caisson were extended vertically with all haste; meanwhile two additional rings of iron were placed in position, and the top was brought about 20 feet above the water. While this work was in progress the structure gradually bit farther and farther into the sand, until at last it secured a firm hold. At the earliest possible moment the air-compressors were set to work, and air was driven into the space between the cutting edge and the roof, in which the men were to work. This space was 40 feet square and 7 feet deep. The greater pressure of the air drove the water out from this space, and the men were able to enter through the air-lock and to work upon a dry surface, isolated from the surrounding sea by the fence formed by the cutting edge.