194 Natural and Artificial Flight. (April, 
“ How the Figure of 8 is Unravelled, and becomes a Waved 
Track.—When the inse¢t flies in a horizontal dire¢tion, and 
the speed attained increases with the duration of flight, the 
wing reciprocates less and less perfectly, because the figure 
of 8 sweeps described by it are converted into a looped and 
then a waved track, as represented atabcdefghijkIlm 
nopqrst of Fig. 6; the corresponding looped waved track 
due to recoil being shown at similar letters of Fig. 7. The 
body of the insect is carried along the curve represented by 
the dotted line of Fig. 7. 
The waved track formed by the ascent and descent of the 
wing in the progressive flight of the bat and bird is origin- 
ated in a similar manner, but in this case the figure-of-8 
} eae een enema mennns 
Qu 
emcee wns cen ecccccwe mcs cneen = ccger ese —aeas nee” 
Figs. 8and g show the more or less perpendicular direétion of the stroke of 
the wing in the flight of the bird (gull)—how the wing is gradually 
extended as it is elevated, 1, 2, 3 of Fig. 8—how it descends as a long 
lever until it assumes the position indicated by 4 of Fig. 9—how it is 
flexed towards the termination of the down stroke, as shown at 4, 5, 6 of 
Fig. g, to convert it into a short lever, a b, and prepare it for making the 
up stroke. The difference in the length of the wing during flexion and 
extension is indicated by the short and long levers a b and c d of Fig. 9. 
The sudden conversion of the wing from a long into a short lever at the 
end of the down stroke is of great importance, as it robs the wing of its 
momentum, and prepares it for reversing its movements. 
loops are disposed more vertically, because of the more 
vertical direction of the stroke as represented at I 2 3, 
4 5 6 of Figs. 8 and g. 
The unravelling process is shownabcdefghijkimn 
o p of Fig. 10; the completed wave-track being seen at s fu 
v w of the same figure.” 
“The Natural Wing, when Elevated and Depressed, must move 
forwards.—It is acondition of natural wings, and of artificial 
