Porter' s Porter of Washington next appeared with a satisfactorily-working model, and later on with a gigantic air-vessel (pi. 6o, fig. 9). Its balloon bad a length of nearly 363 feet and a g,rreatest diameter of about 36;< feet. Its car formed a saloon 59 feet long by 8,1'; feet wide and hig,h, and the motive-power was supplied by a double-cylinder steam-engine of four-horse power. Ou the trial-trip of the apparatus it was, however, found that the linen used in the envelope had been so rotted by the varnish with which it was coated that it allowed the hydrogen gas to escape; and a satisfactory trial of the device does not appear to have been made.
Later on, Mariott, in California, constructed a similar air-vessel, with which, it was claimed, satisfactory experiments were made, July 2, 1869, bv the "Aerial Steam-Navigation Company;" but nothing seems to have been done thus far in regard to the proposed building of a larger vessel.
De La' me' s Dirigible consequence of the interest in aero nautic experiments awakened by the siege of Paris, Dupuy de Lame designed the apparatus seen in Figure 2 (Pi. 61). A large vessel with a balloon hav ing a capacity of about 123,500 cubic feet was constructed according to this design, and on February 2, 1872, made a successful trial-trip to Fort Vincennes. The balloon was filled with hydrogen, and the car carried four teen persons, of whom seven at a time were employed in working at a cap stan which controlled the shaft of a propeller having two wings each feet in length. With this apparatus a speed of six miles per hour was attained, and a deflection of twelve degrees from the direction of the wiud. The motive-power was less efficient than that employed by Giffard.
Haenlein' s Dirigible satisfactory trial-trip is also said to have been made in 1873 in Braun with a similar construction patented in 1865 by Haenlein. This vessel was provided with a supplementary air reservoir, or air-pocket, the principal object of which was, however, to keep the balloon tense even when gas was withdrawn from it. Gas was, how ever, uninterruptedly withdrawn by the gas-engine which supplied the motive-power. This motor was of somewhat peculiar type, having four cylinders, and possessing other special features designed to secure lightness. The decrease in ascending-power caused by the withdrawal of gas for driv ing the engine was to be compensated for chiefly by the evaporation of the water used for cooling the cylinders of the machine, and further by throwing out ballast.
ilfotors.—All the experiments made in this direction have demonstrated that rudders used with the application of motive-power allow sufficient steering of an aerial vessel in a calm, so that motion in any desired direc tion may be effected; and it is claimed, also, ,that satisfactory progress has been made in a calm air and with a moderate wind. But considerable cur rents of air cannot be overcome, and, besides, the carrying-power is greatly reduced by the IN-eight of the motor. The solution of the problem of con structing a motor which with the required power shall be considerably lighter than those existing at the present time would bring- the question of the practicability of guiding aerial vessels nearer its solution. Alu minium, on account of its lightness, may furnish the material desired, but on acCount of its high cost it cannot yet be made available.
considers the gas-motor as best adapted for the purpose, and the use of hollow parts in the construction of the engine as the most effective method for reducing weight to the lowest degree, this being not only in imitation of the hollow-boned skeleton of the bird, but also in accordance with a true a' ichrm of the doctrine of strength. Besides, the hourly consumption of gas amounts only to 25 cubic feet per liorse-power; so that a volume of, say, t5o,000 cubic feet would not be notably decreased in an ordinary run.
rissamlicr' s a French savant, and a pupil of Giffard, was the first to conceive the idea of einploying electri city as the motive-power for a navigable balloon in place of steam- and hand-power. The source of electrical energy which he usecl was the stor age-battery. His first trial was with a small experimental balloon of elon gated form, which, when inflated with hydrogen, preserved an ascensional force of 2 kilogrammes (4.4 pounds). With the storage-battery cell was connected a miniature motor of the Siemens type (weighing about one fourth of a kilogramine, or less than a half-pound), which was made to drive a propeller consisting of a pair of vanes each to centimetres (about 4 inches) long, the battery, motor, and propeller being supported on a plat form suspended from the netting. This navigable balloon was capable of attaining a speed of about 3 metres (nearly io feet) per second. It was ex hibited at the Electrical Exhibition in Paris in ISSt, where it attracted the favorable notice of the judges.