704 The Wings of Birds. [August, 
function to perform as a member of the organized mechanism of 
flight. The curves in the plane of the wing need not be consid- 
ered as they are not concerned with flight, and when the bird is 
in the act of flying they are straightened out so that the wing 
assumes a plane shape. The above four peculiarities we desire to 
note. Firstly, that the wing is practically a thin plane. Sec- 
ondly, that its rear edge is very pliable and elastic. Thirdly, that 
its under surface is rough to motion from rear to front but smooth 
to motion from front to rear. Fourthly, that it is supplied with 
a ledge along its under surface at the front edge. 
Let us now attend to a matter of simple experiment, which 
demonstrates bird flight as I have presented it in the pages of 
this magazine, and which connects the above-described con- 
struction of a wing, which is the organ of flight, with the 
mechanical forces which are operative upon it. A few cents 
worth of material and the expenditure of a little time is required, 
a which, coupled with a minimum of mechanical expertness, will 
= suffice. The movements following changes made in the plane are 
_ So prompt and emphatic that there is no mistaking them. 
If we take a sheet of light, strong paper, such as goes into the 
construction of fireworks, and stretch sixteen by forty inches of it 
tightly on thin strips of bamboo, so as to present a plane surface on 
_ one side, and fasten a four-ounce weight in the center beneath by 
threads to the four corners, we will have a miniature parachute. 
By putting its upper surface against the ceiling and permitting p 
to fall, it will descend vertically if we have it well balanced. It is 
= Obvious that the entire column of air from the ceiling to the floor 
ing. Hence the zone of air under the plane, acted upon by it, 
_ would be pyramid-shaped with a base sixteen by forty inches, a 
_ top line twenty-four inches long and a height varying with the 
ward, and there would be a steady flow or slipping of the com 
pressed air along the surface in all directions from the center. 
like in all directions no lateral motion would occur. If we now 
take some lar: ge-grained, light sawdust and mucilage, and thinly 
‘le one-half of the under surface from one of the long edges 
_ velocity of the fall of the plane, with the apex pointing down- 
his slipping would cause friction on the surface, which being 
