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 455 meters (36 feet) high. While it was in the course of erection I made other successful trips in the ‘‘Santos-Dumont No. 3,’’ the last time losing my rudder and landing, luckily, on the plain at Ivry. I did not repair it. The balloon was too clumsy in form, and the motor was too weak. I now had my own Aerodrome and gas-plant; I would no longer be obliged to empty the balloon after each trip; I would be able, therefore, to experiment for longer periods and with more method.

The summer of the Universal Exposition was approaching; and I wished, too, to win the 100,000 franc Grand Prix d Aërostation that had just been founded in Paris by M. Deutsch (de la Meurthe). The winning of this prize demanded that the trip from the Saint-Cloud Parc d’Aërostation to the Eiffel Tower, around it, and back to the starting-place should be made within half an hour. The regulations obliged the contestant to convoke, on the eve of each trial, the committee that made up the jury of the prize. I had good hopes of winning, but my chief aim was to continue, in any case, the trials which had already given such good results. So I did not hesitate to begin building an air-ship much more important than the previous ones. It was finished on August 1, 1900.

The measurements of the ‘‘Santos-Dumont No. 4’’ were: Volume, 420 cubic meters (14,-830 cubic feet); length, 29 meters (95 feet) ; middle diameter, 5 meters .60 (18$$\frac{1}{2}$$ feet). Beneath it hung a pole-keel of bamboo, 9 meters .40 (31 feet) long; and to the middle of this was attached the saddle, pedals, and part of the frame of an ordinary bicycle. Astraddle of the bicycle saddle I had under my feet the starting-pedals of a 9-horse-power motor, driving a propeller with two wings, 4 meters (13 feet) across. These were made of silk, stretched over a steel frame. With its aluminium hub the propeller, which was attached to the stem (instead of to the stern)of the pole-keel, weighed 28 kilos(61$$\frac{1}{2}$$ pounds). It turned with a velocity of 100 revolutions to the minute and produced, au point fixe, an effort of 30 kilos (66 pounds). The pole-keel and mechanism weighed altogether 300 kilos (660 pounds). A hexagonal rudder—silk stretched over wooden rods—in spite of its great surface of 7 square meters, was light enough to be placed quite at the extremity of the balloon, on the stuff of the envelope itself. The balloon was rather elliptical in form; and though not at all a return to the slender straightness of No. 1, it had so little of No. 3’s podgy compactness that I thought it prudent to put the compensating air-balloon inside it again, this time fed by a rotary ventilator. Being smaller than No. 3, it would have less lifting-power; but this I would make up by going back to hydrogen gas.

Near the saddle on which I sat were the ends of the cords and other means for controlling the different parts of the mechanism—the electric lighting of the motor, the regulation of the carburator, the handling of the rudder, ballast, and the shifting weights (consisting of the guide-rope and bags of sand), the managing of the balloon’s valves, and the emergency rope for tearing open the balloon. It may easily be gathered from this enumeration that an air-ship,even as simple as my own, is a very complex organism; and the work incumbent on theaëronaut isnosinecure.

With this air-ship I made almost daily trials from the Parc d’Aërostation at Saint-Cloud; but my most remarkable trial took place on September 19, 1900, in the presence of the International Congress of Aëronauts. Although an accident to the rudder prevented my making a free ascension, I held my own against the wind, and gave a clear proof of the effective working of an aërial propeller, driven by a petroleum motor. I then resolved to double the power of my motor, by adopting the four-cylinder type, but always without the water-jacket—which had just been invented. On account of this increase in weight, I was obliged to lengthen my balloon 3 meters (10 feet). The Aërodrome itself then became 10 feet too short; and so I added to it and prepared a lodging for the ‘‘Santos-Dumont No. 5,’’ which I was to build in the beginning of 1901.

Inside the Aërodrome, with a velocity of 140 turns per minute, the propeller furnished a traction-power of 55 kilos (121 pounds). It worked so well that I contracted a severe cold in its current of cold air.

To get rid of this I went to the Riviera, where I constructed the keel of the ‘‘Santos-Dumont No. 5’’—a very light and rigid framework measuring 18 meters (60 feet) in length, and weighing but 50 kilos (110 pounds). It was—as it remains—a combination of curved pine scantlings, held together by aluminium joints, with cross-pieces of wood, and consolidated by a web of steel wires. The cross-section of the keel is an isosceles triangle, 1 meter (3$$\frac{3}{10}$$ feet) high, and 80 centimeters (2 feet, 7 inches) at the base. At its rear was attached the propeller, driven by a 16-horse-power motor. The shaft was of hollow steel. The whole was suspended, attached by steel wires, in the axis of the