552 SCIENCE PROGRESS. 



than the old quadrilateral of our playgrounds, and, further, 

 that the combination of two such boxes connected b\- hori- 

 zontal bars, flies as a kite remarkably steadily and stably. 

 Such matters as strength and 7'igidity can well be investi- 

 gated by experiments with kites, which can be conducted 

 at small cost and with little risk, while other more difficult 

 investigations are being pursued by the students of flight 

 proper. Moreover the old taunt of the French plus leger 

 aeronauts that the />/?(s loui^d had never succeeded in ascend- 

 ing in the air has been completely met by Captain Baden- 

 Powell's experiments in which people have ascended to con- 

 siderable heights and descended in safety by means of kites. 



(vi.) Safe landino- has also been successfully accomplished 

 by Lilienthal, Pilcherand others. It is most difficult to learn 

 to land with a horizontal speed on. \\ hen beginning, one 

 is certain constantly to tumble over forwards ; the only way 

 to stop is to get back in the machine and tilt it up in front 

 so as to cheek the forward movement, thereby imitating the 

 action of birds as revealed by M. Marey's photographs, 

 described in his Vol dcs Oiseaitx. Of course this is very 

 difficult at first. 



In order that this feat of landing safely may be accom- 

 plished, the machine must possess an aeroplane of large 

 extent, such as will act as a parachute and encounter the 

 greatest possible resistance. Another feature is that the 

 machine must not be too large a one to be controlled by 

 balancing. The stopping of a machine propelled by a 

 screw presents difficulties. If the screw were reversed, the 

 machine would simply be driven down on the ground. If 

 the screw were driven forwards, it would have its horizontal 

 motion increased instead of retarded. Pilcher proposes in 

 such cases to stop the action of the propeller altogether, 

 and rely on the aeroplane to stop him. The designers of 

 large air ships are, as a rule, reticent on the means to be 

 adopted for bringing them to earth. 



Suuwiary. — Now it will be observed that the conditions 

 for a good flying machine, like the conditions of sensitive- 

 ness and stability of the common balance of our text-books, 

 are to a certain extent incompatible. Every one of these 

 conditions has been fairly satisfactorily dealt with by some 



