THE POSSIBILITY OF SOARING IN HORIZONTAL WIND. 209 
Thirty-two three-quarter inch square holes were cut in a curved 
piece of aluminium (Plate 17, fig. 7), and each hole was fitted 
with a tissue paper valve lifting on the curved side. When the 
chord of the curve was at about zero, A and B sets of valves lifted 
tangential to the leading edge, and C and D sets of valves were 
fluttering with the blast. 
A level sheet of glass with a little water on it was placed in 
the line of blast, and the curved tin (Plate 17, fig. 6) standing in 
the water with a sprinkling of red ochre shows the vortex at a 
negative angle of about 30°. The tin was set at zero, but the 
after edge was slued round to 30° by the rotation of the vortex. 
This is all very well as far as it goes, but something is wanted 
that would eliminate errors of direction of the wind, and some of 
the uncertainty as to the angles, and also to compare the curye 
with the plane surface. So I fixed a horizontal wire on a stand 
and pointed it towards the blast. A sleeve was on the wire 
revolving freely. On opposite sides of the sleeve I attached a 
bulb ended curved piece of aluminium and a piece approximately 
flat, with set screws to fix them at any angle with the direction of 
blast. There was a lead weight for balancing in the plane of 
rotation. There was nothing to stop the sleeve from slipping 
along the wire, which it did not do. 
You will observe that with this apparatus if my personal 
equation gave any advantage to the curve it would be eliminated 
when the sleeve revolved 180°, and that both surfaces received a 
blast of equal intensity, and that placing the two surfaces on 
opposite side of one axis is equivalent to weighing their respective 
lifting powers in a pair of scales. 
The plane and chord of the curve were first set ata slight 
positive angle (Plate 17, fig. 8). In this case the curve easily 
rotated the sleeve against the lift of the plane. There might 
possibly be no vortex under the curve, and the stronger rotating 
force might be due to the greater angle of slope of the after Ari 
of the curve. 
N—Sept.1, 1897. 
