198 PRACTICAL EXPERIMENTS IN SOARING. 



blades have uothiug to do with this, their function being to keep the 

 machine facing the wind. 



Plate XIII, lig. 1, illustrates such a serpentine flight. I started from a 

 hill to the right, the base of which is still visible in the ligure/and 

 soared toward the plain below in a somewhat circuitous path. The 

 photograph was taken at the moment when I had almost turned my back 

 to the plain. The view shown in Plate xiii, fig. 2, was taken at a time 

 when I was lifted and carried upward by a suddenly increasing cur- 

 rent, which impeded progress and rendered me absolutely stationary. 



In Plate xiv, flights are represented in geometric perspective. The 

 lowest dotted line, d e, was described during a calm. Even the expert 

 flyer must descend during a calm at an angle of from 0^ to 10^. 

 The run began upon the top of the hill, near a ; at i I left firm ground 

 and endeavored to glide along the mountain slope, placing the wings 

 at c at such an angle that the pressure of the wind, X, Avould not only 

 supjjort the machine, but also carry it forward. This increased the 

 velocity sufficiently to enter at d into the line of stable flight. Such 

 a maneuver is necessary, because a velocity of 9 meters per second is 

 required for a flight in a calm, while but G meters were obtained by 

 the run. At e the ground has almost been reached, and by raising tlie 

 wings slightly in front the momentum is diminished and a landing 

 eft'ected without serious jar. 



The second line, c/, shows a flight in a moderate breeze, in which 

 the proper position with a downward inclination of 6° had been 

 assumed immediately upon starting. 



Flight against the wind is slower. The distance to be accomplished 

 may be extended by a carefully determined and properly maintained 

 Inclination of the wings; in fact, by careful observation of this tlie 

 soaring may be extended over a distance equal to ten times the height 

 of the starting point. 



During a strong breeze a sinuous line of flight results from the tem- 

 porary support given by the wind at times. This is shown in the line 

 b (f, though such experiments should be. undertaken only by one fully 

 ftimiliar with the management of the apparatus. The indefinable pleas- 

 ure however exi)erienced in soaring high up in the air, rocking above 

 sunny slopes without jar or noise, accompanied only by the wolian 

 music issuing from the wires of the apparatus, is well worth the labor 

 given to the task of becoming an expert. 



Itdo:iS not seem at all impossible that the continuance of such flights 

 may lead to free, continuous sailing in agitated air. 



The results of our present experiments already furnish an indication 

 of the degree of mechanical energy that must be added to that involved 

 in oblique soaring to enable us to gain independent horizontal flight. 



The solution of this problem,* however, would exceed the purposes 

 of the present article, and I content myself by stating that the condi- 



* Leilsvhrlft fur Luflschiffahrt und Physik der Atmosphiire, November, 1893. 



