The method of opening and closing them was one of the many marvels of modern engineering. The heavy steel doors were held up above the openings by a series of friction clutches. Up on the bridge were switches connected with powerful electro-magnets at the side of the bulkhead openings. The operation of the switches caused each magnet to draw down a heavy weight which instantly released the friction clutches, so that the doors would slide down in a second or two into their places, a gong ringing at the same time to warn anyone who might be passing through to get out of the way. The clutches could also be released by hand. But if for any reason the electric machinery should fail, there was a provision made for closing them automatically in case the ship should be flooded with water. Down in the double bottom of the ship were arranged a series of floats connected with each set of bulkhead doors. In the event of water reaching the compartment below the doors, it would raise the floats, which, in their turn, would release the clutches and drop the doors. These great bulkheads were no new experiment; they had been tried and proved. When the White Star liner _Suevic_ was wrecked a few years ago off the Lizard, it was decided to divide the part of her which was floating from the part which was embedded in the rocks; and she was cut in two just forward of the main collision bulkhead, and the larger half of her towed into port with no other protection from the sea than this vast steel wall which, nevertheless, easily kept her afloat. And numberless other ships have owed their lives to the resisting power of these steel bulkheads and the quick operation of the sliding doors. As for the enormous weight that made for the _Titanic’s_ stability, it was, as I have said, contained chiefly in the boilers, machinery and coal. The coal bunkers were like a lining running round the boilers, not only at the sides of the ship, but also across her whole breadth, thus increasing the solidity of the steel bulkheads; and when it is remembered that her steam was supplied by twenty-nine boilers, each of them the size of a large room, and fired by a hundred and fifty-nine furnaces, the enormous weight of this part of the ship may be dimly realized.