210 L. HARGRAVE. 
The plane and the chord of the curve were next set parallel to 
the line of blast (Plate 17, fig. 9). In this case the lifting force 
opposed by the plane to the curve was nothing, although its resis- 
tance was that due to its area and the velocity of the blast, and 
the lift of the vortex under the curve easily overcame this. 
In (Plate 17, fig. 10) the plane was left parallel to the blast, 
and the curve sloped at a negative angle, this angle was increased 
to at least 10° and the lift of the curve still rotated the sleeve 
against the resistance of the plane. 
In (Plate 17, fig. 11) the plane was put at a positive angle of 
6°, that is, 16° between the plane and the curve. The plane was 
now able to rotate the curve against the vortex. Figs. 12, 13, 14, 
15, show the stream lines of the air when it meets a curve set at 
various angles. 
To recapitulate, the experiments show— 
1. That the profile of a soaring bird’s wing and pieces of metal 
of a somewhat similar curve generate vortices on the concave 
surfaces when the chord of the curves makes a negative angle 
with the direction of the wind. 
2. All the concave surfaces are in contact with air moving 
towards the mean direction of the wind. 
3. That the mean pressure on the concave surface is higher 
than on the convex side. 
4, That the chord of the curved metal may make a negative 
angle of 10° with the direction of the wind and still have a higher 
pressure on the concave side than on the convex. 
And the direct inference is that gravity can be entirely counter- 
acted by a volume of disturbed air moving in a horizontal direction; 
and that flying machines of great weight can be held suspended 
in a horizontal wind, and rise vertically without the expenditure 
of any contained motor force. 
ig Having put matters so that anyone can easily repeat my exper- 
ments and elaborate them to the last degree of precision, we n0W 
