During an ascension the rise and fall of the vessel may now be instantly noted on the dial of the statoscope, the temperature, sure and moisture of the atmosphere may be read on the recording instruments, messages may be sent by telegraph and telephone, either by wire or without, and sky and landscape may be photographed.
Kite The kite balloon is a development of the captive spherical balloon, especially constructed and designed for military purposes and deriving its name from the fact that it performs the service hitherto performed by man-carrying kites. The kite balloon is with a series of ballonets at the lower end which are so adjusted that they act as permitting the observer s basket to remain in the air without the disas trous yawing motion which affects the basket suspended from a spherical balloon.
Power Balloons.— It is natural that after the first launching of human passengers in a crude aerostat, many schemes designed to con trol the course of a balloon should be evolved. The investigators of the early days fully knew that if a propelling mechanism could be made to act in conjunction with favorable aerial currents something might be effected. They knew that the wind frequently has different di rections at different levels. They believed that by causing the craft to rise and fall to a suit able stratum, by use of various then known de vices, it could be made to travel in any direction at the will of the pilot.
Several devices for changing the altitude of the balloon were proposed or tried. For in stance, with the Montgolfier, the mere increase or lessening of the fire would cause it to rise or fall. If a gas bag were used it would be sent up or down by dropping Out ballast•or opening up the valve. Not realizing the enormous power, required to propel swift balloons of the very best shape, and to the light of present achievement, the first efforts at a balloon propul sion as viewed to-day could not be seriously re garded by trained engineers, even at the in ception of aeronautics. Historically they call for brief mention. It was in 1784 that Blanch ard made the first real effort to steer a balloon, using a spherical gas balloon, provided with aerial oars and a rudder. An even simpler de vice was that of the two physicists Miolan and Janinet. The balloon was a Montgolfier with a large hole in one side, through which the hot air was to escape with such strong reaction as to drive the bag forward.
In Roberts brothers made a melon shaped balloon of silk and inflated with pure hydrogen, suspended from which was a longish car of white wood. This ship was to be rowed through the air by a crew of six by means of silken oars. A seven hours' cruise was made in the vessel, and before coming down the crew managed to have the envelope navigate a curve nearly one kilometer in radius.
While these experimentations were being carried out, even more important experiments were being made by other inventors. In 1784,
in a letter written to Benjamin Franklin, Francis Hopkinson of Philadelphia proposed to build a balloon of spindle shape and to drive it by means of a wheel-like propeller. This proposed craft, the forerunner of the modern screw-driven motor balloon, antedated the screw-driven boat, the submarine and the aero plane. In 1820 Rufus Porter, an American inventor, and later the original founder of the Scientific American, patented an airship which was decidedly in advance of that day. Its hull was a long, finely tapering symmetrical spindle, suspending a car of similar shape by means of cords, which were vertical at its middle, but more and more slanting toward its ends. Mid way between the hull and car was a large screw propeller, actuated by a steam engine in the car. The inventor, being too poor to develop his airship alone, did little with the patent dur ing his life.
The Henri Giffard was the in ventor of the first dirigible which was success ful both in design and operation. It was a spindle-shaped bag covered with a net whose cords were drawn down and attached to a horizontal pole, from which the car and motor were suspended, and at the end of which was a triangular sail serving as a rudder. To guard against fire, the furnace of the coke-burning boiler was shielded by wire gauze, and the draft, taken from its top through a downward point ing smokepipe, was ejected below the car by force of exhaust steam from the engine, thus obviating, as Giffard asserted, all danger from the use of fire near to inflammable gas. The car hung 20 feet below the suspension pole, and carried a three horse-power engine driving a three-blade propeller 11 feet in diameter, and making 110 turns per minute. The motor com plete, including the engine and boiler without supplies, weighed 110 pounds per horse power. The bag measured 143 feet long, 39 feet in diameter and 75,000 cubic feet in volume. Gif fard reports of his first voyage that although he could not sail directly against the strong wind then blowing, he could attain a speed of 6 to 10 feet per second relatively to the air, and he could easily guide the vessel by chang ing the rudder. Captain Charles Renard of the French War Department continued the good work of Giffard. He manifested uncommonly good judgment and excellent scientific method in combining the researches and contrivances of others with those of his own. As a conse quence he produced the first man-carrying dirigible that ever returned against the wind to its starting point, and the first aerial vessel whose shape and dynamic adjustment even ap proximated the requirements of steady and swift navigation in a surrounding medium pre senting various conditions of turbulence and calm.