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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 62 



balloon hulls designed in accordance with hydrodynamic theory ; 

 also his measurements of the resultant wind force on oblique hulls 

 and wing- forms by the method devised and used by H. Mattullath 

 in 1902; also the resistance of wires and ropes, etc. Prandtl found 

 in fair shapes a large difference between total resistance and the 

 pressural resistance, and ascribed the dilTerence to skin-friction ; but 

 this he did not attempt to measure directly. 



The Deutsche J^ersuchsaristalt fiir Luftfahrt zu Adlershof com- 

 prises one main building used for offices and full-scale aeroplane 

 testing ; one used for construction ; and five small houses each con- 



FiG. 5. — Prandtl's Suspension for Measuring Side Force 



taining an engine testing apparatus. In addition to this plant, it is 

 intended to fly full-scale machines with measuring instruments, and 

 to mount large apparatus on an aerodynamic car pushed by a loco- 

 motive on a railway. 



The laboratory of the main building is a large square room with 

 a tower in its center 100 feet high, on top of which wind observa- 

 tions may be made, and inside of which suspension cords run down 

 to support an aeroplane just above the floor, to determine its moment 

 of inertia. In a corner of the room an aeroplane inverted and 

 weighted with sand, as in Langley's method, was under test for 

 stress and strain of its wing framing. In another corner was an 

 apparatus for measuring the force applied to the controls of an 



