Captive balloons, as the name signifies, are balloons which are held captive to the earth by means of a cable. The cable is usually arranged to be let out and hauled in by means of a wind lass or drum operated by hand or by mechanical power. Captive balloons are much used iu mili tary operations and for amusement purposes, and to some extent for scientific observations. One of the largest captive balloons ever em ployed was at the Paris Exposition of 1878, where it made ascents with passengers from the Tuileries quadrangle. This balloon had a capac ity of over 25,000 cubic yards and was made of canvas.
Dirigible balloons are balloons arranged with steering apparatus or propelling machinery by which the direction of their flight can be regu lated at will. Various attempts have been made to design and operate dirigible balloons, but those which have attained the greatest success are: The experiments of M. Gaston Tissandier, made in 1883: the French army tests, made a year or so later, and, finally, the notable experi ments of Count Zeppelin, made in the summer of 1900, and of M. Santos-Dumont, made in 1901. The balloon with which experiments were made by M. Tissandier was 91 feet long and 29 feet in diameter, built in the shape of a very thick cigar, with both ends pointed. The envelope was made of thin cloth covered with an impermeable varnish, and from it was hung by means of the usual netting and suspenders a car containing an electric battery supplying current to an elec tric motor which operated a screw propeller feet in diameter and having two blades. A tri angular silk rudder was fitted above the pro peller in much the same relative position as the rudder of a steamship, and arranged so as to he operated from the car. The total weight of the propelling machinery, the car and the appurte names, exclusive of 850 pounds of ballast. was 1200 pounds, while the balloon itself weighed 600 pounds. With the propeller making ISO revo lutions per minute this balloon was able to maintain its position against a wind blowing 6.8 miles per hour, and when traveling with the wind to deviate to one side or the other with ease. The French Government balloon, whose construction was suggested by Tissandier's ex periments, was designed by MM. Renard and Krebs on similar lines to. but somewhat longer in comparison with its diameter than, Tissan dier's. Seven ascents were made with this bal loon during 1884-85. with the following prac tical results: In five of the ascents the voyagers were able to return to their starting point, and in one instance a velocity of 13 miles per hour was attained independently of the wind. The
airship in which Count Zeppelin made his notable voyages of 1900 consists of a row of seventeen balloons, confined like lozenges in a package, in a cylindrical shell 420 feet long and 39 feet in diameter. with pointed ends. These balloons serve to lift the structure in the air, where it is driven forward or backward by means of large screw propellers operate,d by benzine motors. A pair of rudders, one forward and one aft, serve to steer the "airship." The crew and passengers occupy two aluminum ears suspended forward and aft, below the body of the balloon shell. From these cars, which are connected by a speaking tube, all the machinery of the "airship" is operated. The "airship" is made to run on a horizontal or in clined plane by means of a weight, which can he moved hack and forth,. on a cable underneath the balloon shell. When the weight is far aft, the bow of the ship points upward and the move ment is upward: and when the weight is far forward, the movement is downward, and when the weight is exactly in the centre of the ship, the travel is horizontal. The aluminum ears are each 20 feet long and feet high. The frame wo•k of the shell is aluminum wire covered on the top with soft ramie fibre protected by pegamoid, and on the bottom with light silk. The seventeen gas bags, made of a special cotton material, are all separate from one another, and there is a safety valve for each. although only four have outlet valves. The Daimler benzine engines, one in each car, are of 16 ho•se-power capacity each. and weigh 715 pounds each. The screw propellers. two for each engine. have four blades and are feet in diameter. At the first trial of toe Zeppelin airship on July 2, 1900. with five persons in the cars. it rose 1300 feet above Lake Constance and traveled miles in 17 minutes in the direction desired. An accident to the slid weight and to one of the rudders caused a de ," scent to be made, which was accomplished with perfect ease. At a succeeding trial on oetober 17, the airship attained a height of nearly 2000 feet, and there remained poised for 45 minutes. It then made a series of tacks, and described a circle of about 6 miles circumference. The wind exceeded a velocity of about 7 miles per hour, and the airship made headway against this wind for a considerable distance. After remaining in the air for about one hour, the ship descended to the lake with great ease, and was towed to its shed. In steering, stability, and equilibrium the test was pronounced very successful.