42 SMITHSONIAN CONTBTBTJTIONS TO KNOWLEDGE VOL. l!7 



It cannot be too clearly kept in mind that these values refer to horizontal 

 flight, and thai for this the weight, the work, the area, the angle and the velocity 

 arc inseparably connected by the formula' already given. 



It is to be constantly remembered also, that they apply to results obtained 

 under almost perfect theoretical conditions as regards not only the maintenance 

 of equilibrium and horizontally, but also the rigid maintenance of the angle a 

 and the comparative absence of friction, and that these conditions are especi- 

 ally " theoretical " in their exclusion of the internal work of the wind observ- 

 able in experiments made in the open wind. 



Experiments in the Open "Wind 



I have pointed out 2 that an indefinite source of power for the maintenance 

 of mechanical flight, lies in what I have called the " internal work " of the 

 wind. It is easy to see that the actual effect of the free wind, which is filled with 

 almost infinitely numerous and incessant changes of velocity and direction, must 

 differ widely from that of a uniform wind such as mathematicians and physi- 

 cists have almost invariably contemplated in their discussions. 



Now the artificial wind produced by the whirling-table differs from the real 

 wind not only in being caused by the advancing object, whose direction is not 

 strictly lineai-, and in other comparatively negligible particulars, but especially 

 in this, that in spite of little artificial currents the movement on the whole is 

 regular and uniform to a degree strikingly in contrast with that of the open wind 

 in nature. 



In a note to the French edition of my work, I have called the attention of the 

 leader to the fact that the figures given in the Smithsonian publication can 

 show only a small pari of the virtual work of the wind, while the plane, which is 

 used for simplicity of exposition, is not the most advantageous form for flight ; 

 so that, as 1 go on to state, the realization of the actually successful aerodrome 

 must take account of the more complex conditions actually existing in nature, 

 which were only alluded to in the memoir, whose object was to bring to attention 

 the little considered importance of the then almost unobserved and unstudied 

 minute fluctuations which constitute the internal work of the wind. 1 added 

 that I mighl later publish some experimental investigations on the superior effi- 

 ciency of the real wind over that artificially created. The experiments which 

 were thus alluded to in 1893, were sufficienl to indicate the importance of the sub- 

 ject, but the data have not been preserved. 



What immediately follows refers, it will be observed, more particularly to 

 the work of the whirling table. 



'See "Internal Work of the Wind" ; also Revue ile L'Aeronautique, ?,' Livraison, 1S93. 



