first balloon in 1898. It was in the form of a cylinder, terminated at each end by a cone, and was 82 feet long and nearly 6 feet in diameter, with a capacity of 6400 cubic feet. A basket suspended from the balloon carried a 1½ horse-power gasoline motor, which operated a screw propeller. To provide the necessary fore and aft trim for ascent and descent when under way, the inventor made use of bags of ballast which could be attached or removed at will from ropes suspended from the forward and after part of the balloon and accessible from the basket or car. With this balloon M. Santos-Dumont made an ascent in the autumn of 1898 which nearly resulted fatally to himself; the failure of an air-pump to work resulted in a partial collapse of the balloon, which fell 1300 feet to the ground. Aside from the air-pump accident, the success of this trip was unusually encouraging: the balloon proved perfectly dirigible in the light winds prevailing at the time of the trip. A second balloon, built exactly like the first, but larger, was never used by M. Santos-Dumont, owing to the fact that in some experiments made with his first balloon when captive the conclusion had been forced upon him that the model was incorrect. A third balloon, shorter and very much thicker, was completed in the summer of 1899. This balloon was 66 feet long, 11½ feet greatest diameter, and 17,600 cubic feet capacity, and into the construction was introduced the novelty of what the inventor termed a keel. This keel was nothing more or less than a bamboo pole, 30 feet long, fixed lengthwise to suspender cords just beneath the balloon, which supported the basket and other apparatus. The most notable trip made with this balloon is thus described by the inventor: "On November 13, 1899, I started from Lachambre's atelier in Vaugirard on the most successful trip I had yet made. From Vaugirard I went directly to the Champs de Mars, where I practiced describing figure 8's. The airship obeyed the rudder beautifully. After circling around the Eiffel Tower a number of times. I made a straight course to the Pare des Princes at Auteuil; then, making a hook, I navigated to the manœvre grounds at Bagatelle, where I landed." M. Santos-Dumont found that this balloon was too clumsy and the motor too weak, and he built a fourth, 95 feet long and 9 feet in diameter, elliptical in shape, with a capacity of 14,800 cubic feet. In this balloon the keel was a long framework of bamboo and wire, which carried directly — there being no suspended car — a 7 horse-power motor with its propeller and other mechanism. The operator managed his machine seated on a bicycle saddle attached to the keel. With this balloon M. Santos-Dumont made numerous short trips during the Paris Exposition of 1900. Balloon No. 5 was made by cutting balloon No. 4 in half and inserting a cylindrical piece sufficient to increase its length to 109 feet. A 16 horse-power motor was adopted. The keel was a 60 foot framework of pine and piano wire, and into it, 20 feet from the stern, was fixed the motor, while the operator occupied a basket 23 feet from the front end or stem. On August 18, 1901, M. Santos-Dumont navigated this balloon from St. Cloud to and around the Eiffel Tower, and was approaching the starting point when the balloon collapsed, and the whole structure, with its operator, was precipitated upon the roof of the Trocadero Hotel, where it hung, the keel spanning the space between the two roofs. The sixth balloon of M. Santos-Dumont was like the previous one, except that it was longer, thicker, and more nearly ellipsoidal in shape. On October 19, 1901, this balloon succeeded in making a trip from St. Cloud to and around the Eiffel Tower, and then back to the starting point, in 30 minutes, 40¼ seconds. The first part of the trip to the tower was with the wind, and was made in 8 minutes, 45 seconds, but the return trip was against the wind, and required 20 minutes, 30 seconds to complete. The remaining 1 minute 40¼ seconds were consumed in descending. The trip was undertaken as the result of a prize of 100,000 francs offered to the inventor should he succeed in making the journey in 30 minutes. According to the newspaper accounts, the balloon pitched somewhat when going against the wind, and Santos-Dumont, when he descended, said the motor suddenly stopped while the balloon was at a little distance from the tower. He thought he might have to descend; but, luckily, he succeeded in getting the machine started again. From that time on, the motor worked satisfactorily.
In closing this reference to dirigible balloons, it is important to remember that the successful trials so far made have been with very light winds blowing. Before such balloons can be considered to have reached a practical basis they must be able to travel at a speed which will overcome at least all ordinary winds, and also have a steering power which will preserve their position in variable winds, as well as in winds of velocities which require the full power of the propelling machinery to overcome. These are questions regarding which there is much uncertainty.
High ascents in balloons have been made by a number of aëronauts. On September 5, 1862, two English aëronauts, Messrs. Coxwell and Glaisher, starting from Wolverhampton, England, ascended 37,000 feet, or fully seven miles. At a height of 5½ miles one of the aëronauts became insensible and the other very nearly so; at the height of 4 miles railway trains could be heard, but at a height of 6 miles there was perfect silence. On April 15, 1875, M. Tissandier, the inventor of the dirigible balloon previously described, and two others rose from Paris, France, a height of 5⅓ miles. M. Tissandier alone survived the trip, his companions dying in mid-air, and he himself being rendered unconscious. These are the two highest balloon ascents recorded in which living beings were passengers.
Scientific research by means of balloons has been undertaken in a number of instances, the most notable attempt, perhaps, in recent years being that of the arctic explorer Andrée to reach the North Pole in the summer of 1897. As is well known, the explorer and his companions perished without accomplishing anything. The most fruitful scientific results so far obtained by ballooning have come from the study of the magnetism, humidity, temperature, and chemical composition of the air at high altitudes. The first ascension of any value for these purposes was that of Gay Lussac, in 1804, from Paris. The balloon rose to 23,000 feet, and the fall in temperature was 67° F., or 1° in 340 feet. Specimens of air collected at the highest point showed precisely the same composition as at the earth.
