VIII
KITES, SUNDIALS, PATENTS
The next day, just as Mr. Gregg returned from his office, Fred, Jessie, and George landed on their new dock from the Caroline. They had been for a sail on the river, and Jessie was quite enthusiastic over the trip. "Fred was a real good captain. Why, papa, he let me steer the boat all by myself, and taught me so well I didn't have any collisions."
An hour or so later the boys, Jessie, and Mr. Gregg, retired to the den.
After questioning the boys regarding the previous talk, to discover if they remembered the main points, Mr. Gregg said he would now tell them something of kites and kite flying.
"The highest kite ascent yet recorded was made at the aeronautical observatory at Lindenburg, (Prussia) on November 25, 1905, 21,100 feet being attained. Six kites were attached to one another with a wire line of nearly 16,000 yards in length. The minimum temperature recorded was 13 degrees, F.; at starting the reading was 41 degrees. The wind velocity at the surface of the earth was eighteen miles an hour, and the maximum altitude it reached was fifty-six miles an hour. The previous height record by a kite was nearly 1,100 feet lower, and it had been reached from a Danish gunboat in the Baltic. These ascents were wonderful, for it is not an easy matter to train a kite higher than a given altitude, for several reasons. The higher a kite rises the more string it will require, and this tends to weight down the plane or kite.
The wind, too, acting on the string, tends to retard the upward flight and to cut short further ascent. When an ordinary kite reaches a height of 1,200 or 1,500 feet, it is doing very well; and few exceed this height. When Benjamin Franklin angled in the clouds for lightning, his kite did not attain an altitude of more than 1,000 feet, which was quite sufficient for the purpose he had in view. When Franklin flew his kite, he was so afraid of ridicule that he took a small boy with him to carry the kite and string, in order to prevent his neighbours from thinking he was going 'kite flying.' In these days when a man is seen flying a kite, people very naturally imagine him to be an aeronaut, studying the science for the purpose of improving or inventing a flying machine of some kind—for which there seems to be ample room.
Fig. 54. Science of kite-flying
"The first thing a beginner in the science of aeronautics will want to know is, 'Why does the kite or machine lift itself off the ground?' If you take a kite and hold it in an inclined position, the wind on the lower side will have a tendency to blow it backward; but as it is held by the kite string, this movement is impossible, and so it is inclined to rise in the air (see [Fig. 54]). If we construct a large plane and equip it with a motor operating a screw which pushes or pulls the plane along through the air, the result is the same as if the plane were anchored, and the wind hits the lower surface of the inclined plane, thus forcing it up. Also, we find, within certain limits, the more you incline a plane the more lift or upward thrust will it give; but it will take more power to drive it through the air, and the faster the plane is driven through the air the less surface is required to support the weight. A matter of great importance in the construction is the shape of the plane, and the shape of the vertical section through the same. The shape of these planes has been explained in Figs. [43] and [44], and the reasons were given why these shapes were considered the proper ones for the purpose.