APPLIED MECHANICS LECORNU. 279 



On the experimental side, we must mention the beautiful researches 

 undertaken by Eiffel in the laboratory he has built near the Champ 

 de Mars. It has just been removed to Auteuil. The essential part 

 is a room traversed by an ah' current, 2 meters in diameter, provided 

 by a centrifugal blower. The velocity of the air may be made as 

 great as 32 meters per second, or 115 kilometers per hour. There is 

 at one side another blower which furnishes air, with a section 1 meter 

 in diameter, but of which the velocity may be raised up to 144 kilo- 

 meters per hour. The motive power is furnished by a monophase 

 current from the place at the Champs Elysees and previousl}^ trans- 

 formed into a direct current. 



Eiffel's laboratory therefore uses the so-called tunnel method. 

 De Guiche uses m his experiments an entirely different method, 

 studying the action of the air upon surfaces of various form carried 

 by an automobile. We might call the latter an open-air method. 

 At the Institut d'Aerodynamique of Saint-Cyi*, established through 

 the liberality of Deutsch de la Meurthe, an open-air method is also 

 used, except that the surfaces under study are carried on a wagon 

 moved electrically along a track 1,400 meters long. A third method, 

 which may be called that of a race course, is used at Saint-Cyr in 

 order to be able to work when the atmosphere mthout is not suffi- 

 ciently calm. The diameter of the course has been made 38 meters 

 so as to diminish as much as possible the influence of its curvature. 



There are other aerodynamical laboratories in other countries, 

 notably m Italy and in Russia. But whatever may be the scientific 

 interest ui the experiments carried on in any laboratories, the con- 

 clusions which we may draw from them, when applied to aviation, 

 must alwa3"s be subject to certain reservations when applied to 

 practical aviation. In order to know exactly what happens on an 

 aeroplane, the mciisiu-ing apparatus must be installed upon the 

 aeroplane itself in full flight. Legrand and Gaudart Miave already 

 made some experiments in that mamier. It is desirable that their 

 example be followed. 



Before leavijig the domain of aviation, which will yet require long 

 development, I wish to say a word about Doutre's contrivance for 

 stability. This is designed, accordhig to the inventor, to produce 

 automatically the necessary changes for cffectuig the longitudimil 

 stability of an aeroplane. The prmciple is as simple as it is ingenious. 

 A screeii running upon guides in the direction of flight receives per- 

 pendicularly the force of the wuid. To this wing are fastened two 

 other guides parallel to the first and upon which a heavy mass moves. 

 Suitable sprbigs keep the mass in a dctermbiatc position. When the 

 velocity of the aeroplane tends to change abruptly, the movable 

 mass, because of its inertia, is momentarily displaced along the guides. 

 On the other hand, when the velocity experiences a sensible varia- 



