Experiments with non-rigids in Germany was mainly carried on by Major Parseval, who produced his first vessel in 1906. The main feature of this airship consisted in variation in length of the suspension cables at the will of the operator, so that the envelope could be given an upward tilt while the car remained horizontal in order to give the vessel greater efficiency in climbing. In this machine, the propeller was placed above and forward of the car, and the controlling planes were fixed directly to the envelope near the forward end. A second vessel differed from the first mainly in the matter of its larger size, variable suspension being again employed, together with a similar method of control. The vessel was moderately successful, and under Major Parseval's direction a third was constructed for passenger carrying, with two engines of 120 horsepower, each driving propellers of 13 feet diameter. This was the most successful of the early German dirigibles; it made a number of voyages with a dozen passengers in addition to its crew, as well as proving its value for military purposes by use as a scout machine in manoeuvres. Later Parsevals were constructed of stream-line form, about 300 feet in length, and with engines sufficiently powerful to give them speeds up to 50 miles an hour. Major Von Gross, commander of a Balloon Battalion, produced semi-rigid dirigibles from 1907 onward. The second of these, driven by two 75 horse-power Daimler motors, was capable of a speed of 27 miles an hour; in September of 1908 she made a trip from and back to Berlin which lasted 13 hours, in which period she covered 176 miles with four passengers and reached a height of 4,000 feet. Her successor, launched in April of 1909, carried a wireless installation, and the next to this, driven by four motors of 75 horse-power each, reached a speed of 45 miles an hour. As this vessel was constructed for military purposes, very few details either of its speed or method of construction were made public. Practically all these vessels were discounted by the work of Ferdinand von Zeppelin, who set out from the first with the idea of constructing a rigid dirigible. Beginning in 1898, he built a balloon on an aluminium framework covered with linen and silk, and divided into interior compartments holding linen bags which were capable of containing nearly 400,000 cubic feet of hydrogen. The total length of this first Zeppelin airship was 420 feet and the diameter 38 feet. Two cars were rigidly attached to the envelope, each carrying a 16 horse-power motor, driving propellers which were rigidly connected to the aluminium framework of the balloon. Vertical and horizontal screws were used for lifting and forward driving and a sliding weight was used to raise or lower the stem of the vessel out of the horizontal in order to rise or descend without altering the load by loss of ballast or the lift by loss of gas.