anticipated the speed and endurance of the best air ships built toward the close of the nineteenth century, or later. PLATE II. [Illustration: HAENLEIN’S GAS-DRIVEN DIRIGIBLE.] [Illustration: WÖLFERT’S BENZINE-DRIVEN DIRIGIBLE.] [Illustration: SANTOS-DUMONT’S DIRIGIBLE, _NO. 16_. _Photo E. Levick, N. Y._ ] In 1879, Baumgarten and Wölfert in Germany built a dirigible equipped with a Daimler benzine motor, but otherwise not possessing any special merit. An ascension was made at Leipsic in 1880, but owing to improper load distribution the vessel reared on end and crashed to earth. After further experiments, an ascension was made on the Templehofer field, near Berlin, in 1897, but this ended disastrously; for the benzine vapor ignited; the fire spread to the balloon, and the vessel fell flaming to the earth, killing Wölfert and his assistant. Baumgarten had died some years before. In 1897, an aluminum air ship invented by an Austrian engineer, named Schwartz, was launched on the Templehofer field. Its hull was of cylindrical form with conical ends, made of sheets 0.008 thick, and stiffened with an internal frame of aluminum tubes. Being leaky and inadequately driven, it voyaged but four miles, drifting with the wind, then fell to earth with considerable shock. The pilot, a soldier of the Balloon Corps, escaped by jumping, before the vessel struck ground, but the frail unbending hull was soon demolished by the buffeting of the winds as it lay stranded on the unyielding earth. This was the second air ship built after the plans of poor Schwartz, the first having collapsed on inflation. He had, however, the credit of being the first to drive a rigid air ship with a petrol motor, and thus to inaugurate a system of aërial navigation capable of immense development, in the hands of sufficient capital and constructive skill. Thus the rigid type, conceived and crudely tried by Marey Monge and Dupuis Delcourt in the early part of the century, began to approach practical realization toward the end of the century. The process of inflating with hydrogen such a rigid hull is interesting. Schwartz’s plan, carried out by Captain Von Sigsfeld, was to place the hydrogen in one or more sacs inside the hull, thus expelling the air and filling the space, then withdrawing the sacs and leaving the hydrogen within. A better plan is to have a single sac inflated with air just filling the hull like the lining of an egg, then to force the gas between the lining and metal wall of the hull, thus expelling the air from the sac, which when completely collapsed can be removed. Practically the same result can be obtained by use of a thin fabric covering one half the inner wall, like the lining of an egg. Further provision can easily be made for manipulating the ballonet in such a case. CHAPTER IV INTRODUCTION OF GASOLINE-DRIVEN DIRIGIBLES