244 Aénial Locomotion. [April, 
At the inner part, towards the body, the wing inclines considerably both down- 
wards and backwards, while near its extremity it is horizontal, and sometimes 
slightly turned up, so that its under surface is directed somewhat backward.””* 
It is worthy of remark that the curves of the wing 
described and delineated by Dr. Pettigrew are reproduced by 
Prof. Marey (compare Figs. 68, 69, and 70 of Dr. Pettigrew’s 
1867 memoir, Linn. Soc. Trans., vol. xxvi., with the right 
wing, Fig. 89, p. 210, of Prof. Marey’s new volume). 
When speaking of the duration of the down and up 
strokes, Dr. Pettigrew observes (Trans. Linn. Soc., vol. xxvi., 
Dey 2OU ema 
“In birds which glide or skim, it has appeared to me that the wing is reco- 
vered much more quickly, and the downward stroke is delivered much more 
slowly, than in ordinary flight ; in fact, that the rapidity with which the wing 
acts in an upward and downward direétion is, in some instances, more or less 
reversed; and this is what we would naturally expe& if we recolle@ that in 
gliding the wings require to be, for the most part, in the expanded condition.” 
Prof. Marey writes in a similar strain. He states— 
‘‘ Experiment proves that the wing of the bird is raised more quickly than 
it descends.”—(P. 212.) . . . ‘‘ Contrary to the opinion entertained by some 
writers, the duration of the depression of the wing is usually longer than that of 
its rise. The inequality of these two periods is more distinctly seen in birds 
whose wings have a large surface and which beat slowly.”—(P. 228.) 
Weight, according to Dr. Pettigrew, contributes to hori- 
zontal flight. In illustration he states (Trans. Roy. Soc. 
Edin., vol. xXxvl., pp. 355, 356)— 
“If two quill-feathers are fixed in an ordinary cork, and the apparatus 
allowed to drop from a height, the cork does not fall vertically downwards, but 
downwards and forwards in a curve. When artificial wings, construéted on 
the principle of natural ones, are allowed to drop from a height, they describe 
double curves in falling, the roots of the wing reaching the eround first, which 
proves the greater buoying power of the tips of the wings. Weight, when 
acting upon wings, must be regarded as an independent moving power.” . 
“ The wings of the bird form a natural parachute, from which the body depends 
both during the down and up strokes.” —(P. 371.) 
Prof. Marey performs similar experiments, and arrives at 
similar conclusions. Thus he explains (p. 217) that if a 
sheet of paper folded in the middle, with a wire loaded at 
one end and fixed in the bent portion, be allowed to fall, the 
apparatus will not descend vertically, but will follow an 
oblique trajectory; and that if the corners of the paper be 
bent, and the concavity directed downwards, the apparatus 
will in falling describe a double curve. 
“The wings are attached exactly at the highest part of the thorax, and 
consequently, when the outstretched wings act upon the air as a fulcrum, all 
the weight of the body is placed below this surface of suspension. Thus the 
* It is evident, from the succeeding paragraph to above quotation from 
«« Animal Mechanism,” that Prof. Marey had read Dr. Pettigrew’s observations 
to which we have just referred. 
