The _Petrel_, the air ship used at the dynamic exposition, was built by the Mount Carmel Aeronautic Company at their works in Chicago, and sent by rail in sections to Coronado Beach, where she was put together. She was cigar-shaped, one hundred feet in length and twenty feet in diameter, and was built of butternut—the toughest of the light woods. Her engines, with their fans and propellers, as well as the gas generator and tank for benzine, were all constructed of tempered aluminum, made by the new Kentucky process, at a cost of only eight cents per pound. Being stronger and tougher than the finest steel, and only one-third the weight of that metal, aluminum was especially adapted for the construction of air ships. The machinery of the _Petrel_ was propelled by a gas generated from benzine. The fluid was carried in an air-tight aluminum tank, from which it passed, drop by drop, to the generator. This gas, almost as powerful as the vibratory ether discovered by Mr. Keely, was much safer because more certainly controlled. The _Petrel_, with all her machinery in place, with two tons of benzine in her tanks, and ten men on board of her supplied with sufficient water and food for use for fifteen days, weighed but ten tons, and the force generated from two tons of benzine was sufficient to lift her, with a freight of ten tons more, to a height of five thousand or even ten thousand feet, and, without any aid from her folding aluminum parachute, was able to maintain her there for a fortnight, at a speed—in a still atmosphere—of fifty miles per hour. No balloon was attached to the _Petrel_, as she relied entirely upon her paddles and wings both for propulsion and as a means of maintaining herself in the air. She was constructed upon the principle of aerial navigation furnished by the wild goose. That bird maintains himself in the ether during a flight of hundreds of miles without a rest, simply because his strength, or muscular power, is greater, in proportion to his weight, than that of creatures who walk upon the ground. Man could always have constructed wings of silk and bamboo which would have enabled him to fly if he had only possessed the strength to flap his wings.