1886.] The Wings of Birds. 707 
soaring birds moving at times at the rate of 150 feet per 
second, 
Motion of the planes, therefore, is best derived from their own 
activities. This can readily be obtained in still air by using fine 
shot for the weight in an oil-silk bag with a thin neck opening 
into another placed lower and fastened to the corners of the plane 
by separate strings. The neck should be made to allow two 
pounds of shot to flow through it in about ten seconds; as the 
shot reached the lower bag the plane would be slanted by draw- 
ing on the longer front and shorter rear strings. 
With 150 feet fall this construction will give motion under the 
resolution beautifully. Nothing can exceed the graceful curva-. 
ture of its movements excepting similar ones made by the soar- 
ing birds. As acceleration passes into uniformity and the total 
force is expended in the work on air, as the shifting balance in- 
clines the plane transforming the vertical, ample force is on han 
in the condensation to resist the downward slanting impulse. If 
the adjustment is correct, holding the plane on the right incline, 
horizontal motion will occur until it passes out of sight. More 
inclination will cause upward slanting direction. If the incline 
be so great as to throw too much of the resolved gravity into the 
plane for the forward thrust to cope with, speed will slacken and 
finally motion to the front will cease and be reversed on the down- 
ward slant backwards, and the frail machine become a wreck in 
an instant by violently striking the earth. I have floated these 
planes from the lantern of Egmont light at the entrance of Tampa 
bay, on the Gulf coast of Florida, when the air was so still that a 
handful of down, from the breast of a pelican, thrown from the — 
top would quietly sink along the shaft to the ground. 
To one who is familiar with the soaring birds, and has made a 
study of their habits, these floating planes present little that is _ 
-iteresting. They imperfectly imitate the birds and do nothing — 
that the birds can not do better. The latter present a plane with - 
automatic balance as well as a selfacting steering apparatus, and ; 
are so plentiful that they can be studied at any time, But the 
_ Panes serve to explain the wing admirably, and after witnessing — 
< their performances with none, and either, and all of the contri- 
vances for producing forward thrust, but little more need be said _ 
or done explanatory of their functions. 
_ From the fore-leg of a reptile to this wing is doubtless a long 
