Feb, i6, j888] 



NATURE 



371 



. wing, the existence of which one would not suspect from 

 the profile representations. This curvature appears at the 

 end of the depression of the wing, at the moment in 

 which the joints begin to bend upwards in order to pre- 

 pare for an ascent. Hence results a spiral aspect of the 

 wing, recalling the form which Mr. Pettigrew considers 

 the essential element in a bird's propulsion. But we must 

 observe that this form is only produced at the very close 

 of the act of descent, at the ^'^ point mart" of the wing's 

 action, as we say in mechanics, and at a moment in 

 which it, having become passive, is about to remount by 

 the resistance of the air. These figures also show a fact 

 wholly unforeseen — namely, that the movements in flying 

 are not symmetricaL It had been previously supposed that 

 the bird, when desirous of turning laterally the direction 

 of its flight, executes movements more extended from the 

 side which is to progress most rapidly ; that is to say, 

 that it gives more amplitude to the movements of the 

 right wing if it wishes to turn to the left, and reciprocally. 

 It is scarcely needful to say that photochronography con- 

 demns entirely the hypothesis in which it was supposed 

 that one of the wings of the bird could bend more frequently 

 than the other ; the movements of the two wings are 

 perfectly synchronous, if not equal, in extent. It is seen, 



in short, from these representations, that the body of the 

 bird inclines and moves in different ways, so as to carry 

 its centre of gravity to one side or the other, according 

 to the necessities of the equihbrium. The bird whose 

 attitudes are portrayed in Fig. 6 seemed careful to bear 

 the weight of its body to the left on account of the 

 smaller surface of its right wing, from which some 

 feathers were missing. 



The representations taken in front and a little ob- 

 liquely, as in Fig. 7, give also useful information. They 

 show that the extremity of the wing — a part of the organ- 

 ism in full activity, since it strikes the air with greater 

 speed — presents, at the time of lowering, changes of 

 surface whicli the secondary remiges extending from the 

 carpus to the shoulder do not offer. Th^rp exists in the 

 wing feathers of the different orders a species of separation, 

 showing that the carpal articulations are the seat of a light 

 twisting movement favourable to the bending of the surface 

 of the carpal remiges. In these representations may also be 

 readily seen the bending and convergence of the wings at 

 the close of their lowering, the depression which the ante- 

 rior side of the wing presents at this moment from the 

 effect of a flexion beginning at the elbow. In order to 

 follow in all their details the changes of movement in the 



Fig. 7. — Sea-gull flying obliquely in the direction of the photochronographioapparatus. (Fac-simile of instantaneous photograph taken by the author.) 



wings, it has been necessary to make many experiments, 

 so as to obtain, during a single stroke of the wing, ten or 

 twelve successive views of the bird seen under each of 

 these different aspects. 



These representations having once been obtained, I 

 was in possession of all the elements necessary to under- 

 stand completely the motions of the wings according to 

 the three dimensions of space. But in order to repre- 

 sent them, figures in relief were necessary ; and circum- 

 stances were favourable to this. At Naples, where I 

 then was, the almost lost industry of casting bronze in wax 

 has been preserved from the most remote antiquity. I 

 modelled in wax a series of figures representing the 

 successive attitudes in a single revolution of the wing, 

 ten for the sea-gull, eleven for the pigeon : these models, 

 when given to a skilful moulder, were reproduced in 

 bronze with perfect fidelity. 



Fig. 8 represents, disposed in a series, and following 

 each other in their order of succession, at intervals of 

 1/88 of a second, the phases of one stroke of a pigeon's 

 wing. 



These bronze figures were made white, in order to 

 render more apparent the effects of light and shade. 

 .Thanks to the multiplicity of the attitudes represented in 



this series, all the phases of the motion of the wings are 

 easily followed : it is seen how they fold, rise, expand, 

 and sink. 



In order the better to understand how the movements 

 of the bird's wing follow each other, of which photo- 

 chronography gives an analysis, I have had recourse to 

 the use of the zootrope, which recomposes them, and 

 gives to the sight the impression of a bird flying. 



The zootrope, represented in Fig. 9, offers this speciality, 

 that it is formed by figures in relief. This is a great 

 advantage from the point of view of the impression which 

 it gives ; in fact, these small figures of birds, arranged in 

 a circle in the apparatus, present themselves to the ob- 

 server under various aspects. 



At the beginning of the movement the bird's backs are 

 seen ; then, in their circular course, they present their 

 sides, pass across in full view, and at last return to the 

 observer. Besides, the movements of the wings, which in 

 nature are extremely rapid, and consequently imperfectly 

 seen, are here much slower, so that the phases may be 

 easily followed, and in an instant, more may be per- 

 ceived than the most attentive observer of the flight of 

 birds could discover by the most careful observation. 



Fig. 9 shows the arrangement of the zootrope;- it 



