CP2−CG2 = 3.3 in. = √(546)7.
FIGS. 1 and 2.—Type sketches of wings by Holmes from a mean of positions taken from his own sketches and photographs, and also from sketches and photographs by Langley.
FIG. 3.—Type sketch of same birds, average type, position of wings.—S. P. Langley.
CP2−CG2 =3.6 in. = √(546)6.5.
FIG. 4.—Average typical position of wings in soaring gull. From memory by S. P. Langley. (The scale here may be taken approximately at 113).
[p287]
I must preface what follows by a little statement of the things which particularly interest me here and which are not a naturalist’s ordinary concern.
First, I want to know the CG of the bird when in flight. You will understand that though there is but one center of gravity (here symbolized as CG), it may be considered (1) with reference to its position on the horizontal plan of the bird with wings extended, when it will always be found somewhere in the medial vertical plane, passing through the body, and usually nearly at a certain point with reference to length, the position thus considered being called CG, or (2) the position of the same CG with reference to a vertical plane passing transversely through the medial line, the position thus considered being called CG2. In the latter case you will understand that the CG which is that of the whole body, wings and all, will be carried more or less upward when the wings are thrown high up, and will be carried temporarily downward when the wings are at their lowest point of the stroke. It would have a certain position when the bird was at rest and another position when it was soaring and the wings were above the body.