146 ANHtTAL REPORT SMITHSONIAN INSTITUTION, 1908. 



came the experiments by Lilienthal, Maxim, Langley, and Chaniite, 

 from 1892 to 1896. 



Specifically, what is the problem of aviation? It consists in 

 launching a heavy body from the earth and in maintaining and 

 guiding it in the air through purely mechanical means. Aviation 

 has also been defined as the science of flying with machines heavier 

 than air, as distinguished from aerostation, the science of ballooning, 

 with apparatus lighter than air. 



It is the solution of this difficult problem of flying that men have 

 sought for a number of years. 



Three different solutions of the problem have been proposed : One 

 is in servile imitation of nature, that represented by the orthopter or 

 wing machine. The second is a purely artificial conception, that of 

 the helicopter or screw machine. The third is that of the aeroplane, 

 which may be considered as a compromise, or a combination of the 

 first two systems. 



The wing machine is, as I have stated, a servile imitation of nature. 

 It is equipped with moving wings, and the machine is lifted by the 

 reaction from the flapping of these wings. One of the principal 

 representatives of this type is that designed by Blanchard even before 

 Montgolfier's hot air balloon ; and, if rumors may be believed, secret 

 experiments are now being conducted in Belgium with the La Hault 

 type of this machine. 



In these wing machines the amount of force upon the air is normal 

 and applied directly, so as to raise the apparatus vertically. It is at 

 once evident that of the two motions in the flapping of the wings, the 

 downward stroke causes the machine to move upward, while the up- 

 ward stroke rather retards this movement. The attempt has been 

 made to overcome this difficulty by the use of valves in the wings 

 that open when the wing is raised and close when it is lowered. 

 None of these machines, however, has given satisfactory results. 



The second type is the helicopter, or screw machine, a purely arti- 

 ficial conception. Paucton was the first to suggest the application 

 of the principle of the screw to aerial navigation, but it remained for 

 de Lalandelle and Ponton d'Amecourt to actually experiment with 

 this system and obtain the first practical results. 



The principle of this system is that of a screw turning upon a 

 vertical axis, and it is the reaction of the air during the movement of 

 the screw that should balance or overcome the weight of the apparatus 

 and cause it to rise. 



These machines are very complicated. A^^ienever a force is applied 

 to a medium such as air, there results a reaction equal to the action 



