The insufficiency of their number in proportion to the size of the ships has not been their only defect, moreover. In order to give an unobstructed passage along the decks it has been the custom to cut doors in the bulkheads, and it has frequently happened that in the confusion following a collision these have been left open, allowing the sea to rush from compartment to compartment, either because they were forgotten or because they refused to work. [Illustration: The Deep-sea Sounding Machine at Work.] In the newest type of ship, as represented by the City of Paris and the City of New York, there are no fewer than twenty water-tight compartments separated by solid transverse bulkheads, which rise from the keel to the saloon deck, eighteen feet above the waterline, and which have no doors or openings of any kind whatever. A few feet from the stem there is a collision bulkhead of extraordinary strength to protect the ship, should she run “bow-on” against any obstacle—a reef, a derelict, or a vessel attempting to cross her path; next, aft of this come three compartments for steerage passengers or cargo; then two compartments for saloon passengers; then four compartments for boilers, coal bunkers, kitchens, and machinery; two more for saloon passengers; one for second-cabin passengers, and two, those farthest aft of all, for steerage passengers or cargo. Each compartment is thus isolated, and only by a blow in the line of the dividing bulkhead could two compartments be flooded at once; the bulkheads also serve in case of fire to prevent the flames from spreading. Still another safeguard becomes possible through the adoption of the twin screw. The propellers are worked by two complete and entirely independent sets of boilers and engines, and these are separated by a longitudinal bulkhead in addition to the transverse bulkheads already described. In a single-screw ship this longitudinal bulkhead is impossible, and the space in which her engine and boilers are situated is her most vulnerable point; if she is struck there with sufficient force to make a fissure large enough to admit any considerable quantity of water, nothing will save her from sinking. In the case of the twin-screw ship, however, we have had the best of evidence, within the past two years, that with one of her engine-rooms flooded and open to the sea, she will still float and be navigable.