Count Ferdinand von Zeppelin first began to experiment in 1898. His first rigid dirigible was 410 feet and the gas-bags contained 400,000 cubic feet of hydrogen, and the net lifting power, after allowing for the engines, fuel, gear, etc., was about two tons. The framework was of aluminum latticework divided into seventeen compartments, fifteen of which had gas-bags. Two cars were attached and in each was a 16 horse-power German Daimler gasoline motor driving two propellers, and the machine gained a speed of 15 miles an hour, which was far in advance of any airship of that period. By this time practically all the fundamentals of construction of dirigibles had been incorporated in these airships. Further refinements were made, more engines and balloonets added, and the length of the dirigible and the volume of hydrogen gas used for inflation was increased, as was also the horse-power, but nothing more in the way of radical changes was employed to the end of the Great War. Therefore a description of the Zeppelin which was brought down in England will serve as an excellent idea of the size of these mammoth airships. The Zeppelin forced to land in Essex measured from 650 feet to 680 feet in length and measured 72 feet across its largest diameter. The vessel was of the stream-line form, with a blunt, rounded nose, and a tail that tapered off to a sharp point. The framework was made of longitudinal latticework girders, connected together at intervals by circumferential latticework ties, all made of an aluminum alloy resembling duraluminum. The whole was braced together and stiffened by a system of wires, arrangements being provided by which they could be tightened up when required. The weight of the framework is reckoned to be about 9 tons, or barely a fifth of the total of 50 tons attributed to the airship complete with engines, fuel, guns, and crew. There were 24 balloonets arranged within the framework, and the hydrogen capacity was 2,000,000 cubic feet. A cat-walk, an arched passage with a footway nine inches wide, running along the keel enabled the crew, which consisted of twenty-two men, to move about the ship and get from one gondola to another. This footway was covered with wood, a material which, however, was evidently avoided as much as possible in the construction of the ship. The gondolas, made of aluminum alloy, were four in number; one was placed forward on the centre line, two were amidships, one on each side, and the fourth was aft, again on the centre line.