Referring now to the side elevation of the Titanic on page 129, it will be noted that the only bulkhead which was carried up to the shelter deck was the first, or collision bulkhead. The second bulkhead extended to the saloon deck, and on the after side of this and immediately against it was a spiral stairway for the accommodation of the crew, which led from their quarters down to the floor of the ship. Here the stairway terminated in a fireman's passage, which led aft through the third and fourth bulkheads, and gave access through a watertight door to the foremost boiler-room. The seven bulkheads, from No. 3 to No. 9, extended only to the upper deck, which, at load draft, was only about 10 feet above the water-line. Bulkhead No. 10 was carried up one deck higher to the saloon deck, as were also bulkheads 11, 12, 13, and 14. Bulkhead No. 15 terminated at the upper deck. Now, it will be asked: what was the factor in the calculations which determined the height of these bulkheads? The answer is to be found in the Board of Trade stipulations, to which reference was made in Chapter IV, page 62. These stipulations establish an imaginary safety line, below which a ship may not sink without danger of foundering. The safety line represents the depth to which a ship will sink when any two adjoining compartments are opened to the sea and therefore flooded. If the two forward compartments are flooded, for instance, the bow may sink with safety, until the water is only three one-hundredths of the depth of the ship, at the side, from the bulkhead deck. If two central compartments are flooded, the ship is supposed to settle with safety until the bulkhead deck at that point is only three one-hundredths of the depth of the side, at that place, above the water. The raising of the height of the bulkheads, by one deck, at the engine-room, is due to the operation of this rule; for here the two adjoining compartments, those containing the reciprocating engines and the turbine, are the largest in the ship, and their flooding would sink the ship proportionately lower in the water. Now it takes but a glance at the diagrams on page 66 to show that the application of the Board of Trade rule brought the bulkhead line of the _Titanic_ down to a lower level than that of any of the other notable ships shown in comparison with her. It was the low bulkheads, acting in connection with the non-watertight construction of the bulkhead deck, that was largely answerable for the loss of this otherwise very fine ship. [Illustration: Courtesy of _Scientific American_ TWENTY OF THE TWENTY-NINE BOILERS OF THE TITANIC ASSEMBLED, READY FOR PLACING IN THE SHIP]