Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/328

 316 FLIGHT elevatin^ surprising quantities of fish, game, carrion, etc. (fig. 28). FIG. 28. Hawk and Pigeon. While, as explained, no definite relation exists between the weight of a flying animal and the size of its flying surfaces, there being, as stated, heavy-bodied and small- winged insects, bats, and birds, and the converse, and while, as lias been shown, flight is possible within a wide range, the wings being, as a rule, in excess of what are required for the purposes of flight, still it appears from the researches of M. de Lucy that there is a general law, to the effect that the larger the volant animal the smaller by comparison are its flying surfaces. The existence of such a law is very encouraging so far as artificial flight is con cerned, for it shows that the flying surfaces of a large, heavy, powerful flying machine will be comparatively small, and consequently comparatively compact and strong. This is a point of very considerable importance, as the object desiderated in a flying machine is elevating capacity. M. de Lucy has tabulated his results as under : INSECTS. BIRDS. D *: &quot;3 J ~ = -c ?J Flying 3 w E m. 3 * x Surface Names. &quot;2 P e * Names. referred ^ fc ? x &quot; to the B| 2 a u Kilogramme. 7 &quot; sq. sq. vds. ft. in. yds. f in. Gnat 1 1 8 92 1 1 104} 7 2 5(i Sparrow 5 14 ^j 5 13 87 Turtledove 4 100^ &quot;2 113 Ti]iuln, or Daddy-long- ^ 3 5 11 Stork 2 20 1 llfi Bee 1 2 74J Crane of Australia ... 130 Meat-flv 1 3 54J 1 2 20 1 2 50 / Stag-beetle ) Lueanus ) (female) f 1 1 39 i cervus ) Stag-beetle ) ( (male) ... j 8 33 Rhinoceros-beetle C 1 .&amp;gt;-&amp;gt; &quot; It is easy, by the aid of tins table, to follow the order, always decreasing, of the surfaces, in proportion as the winged animal in creases in size and weight. Thus, in comparing the insects with one another, we find that the gnat, which weighs 460 times less than the stag-beetle, has 14 times more of surface. The lady-bird weighs 150 times less than the stag-beetle, and possesses 5 times more of surface, &c. It is the same with the birds. The sparrow weighs about 10 times less than the pigeon, and has twice as much surface. The pigeon weighs about 8 times less than the stork, and has twice as much surface. The sparrow weighs 339 times less than the Australian crane, and possesses 7 times more surface, &&amp;lt;x If now wo compare the insects and the birds, the gradation will become oven much more striking. The gnat, for example, weighs 97,000 times less than the pigeon, and lias 40 times more surface ; it weighs three millions of times less than the crane of Australia, and possesses 140 times more of surface than this latter, the weight of which is about 9 kilogrammes 500 grammes ( 25 It) 5 ox. 9 dwt. troy, 20 It) 15 oz. 2j dr. avoirdupois). The Australian crane, the heaviest bird weighed, is that which has the smallest amount of surface, for, referred to the kilogramme, it does not give us a surface of more than 899 square centimetres (139 square inches), that is to say, about an eleventh part of a square metre. But every one knows that these grallatorial animals are excellent birds of ilight. Of all travelling birds they undertake the- longest and most remote journeys. They are, in addition, the eagle excepted, the birds which elevate themselves the highest, and the flight of which is the longest maintained.&quot; l The way in which the natural wing rises and falls on the air, and reciprocates with the body of the flying creature, has a very obvious bearing upon artificial flight. In natu ral flight the body of the flying creature falls slightly for ward in a curve when the wing ascends, and is slightly elevated in a curve when the wing descends. The wing and body are consequently always playing at cross pur poses, the wing rising when the body is falling and vice versa. The alternate rise and fall of the body and wing of the bird are well seen when contemplating the flight of the gull from the stern of a steamboat, as the bird is following in the wake of the vessel. The complemen tary movements referred to are indicated at fig. 29, where the continuous waved line represents the trajectory made by the wing, and the dotted waved line that made FIG. 29 shows how in progressive flight the wing and the body destr be irat-tj. tracts, the crests of the waves made hy the wing (a, c, e, g, j) being placed onpositethe crests of the waves made by the body (1, 2, 3, 4, 5). (Pettigrew, 1870.) by the body. As will be seen from this figure, the winy- advances both u hen it rises and when it falls. It is a con dition of natural wings, and of artificial wings constructed on the principle of living wings, that when forcibly elevated or depressed, even in a strictly vertical direction, they in evitably dart forward. If, for instance, the wing is sud denly depressed in a vertical direction, as at a b of fig. 29, it at once darts downwards and forwards (see continu ous line of figure) to c, thus converting the vertical down stroke into a down, obliqice, forward stroke. If, again, the wing ba suddenly elevated in a strictly vertical direction, as at c d, the wing as certainly darts upwards and forwards in a curve to e, thus converting the vertical up strokes into au upward, oblique, forward stroke. The same thing happens when the wing is depressed from e to /and elevated from &amp;lt;j to h, the wing describing a waved track as at e g, g i. There are good reasons why the wings should always be in advance of the body. A bird when flying is a body in motion; but a body in motion tends to fall not vertically downwards, but downwards and forwards. The wings con sequently must be in advance of the body of the bird if they are to prevent the bird from falling doicnwards and forwards. If the wings were to strike backwards in aerial flight, the bird would turn a forward somersault. That the wings invariably strike downwards and forwards in aerial flight is proved alike by observation and experi ment. If any one watches a bird rising from the ground or ths water, he cannot fail to perceive that the head and body are slightly tilted upwards, and that the wings are made to descend with great vigour in a downward and for ward direction. The dead natural wing and a properly constructed artificial wing act in precisely the same way. If the wing of a gannet, just shot, be removed and made 1 On the Flight of Birds, of Jiat.t, ami of Insects, in reference to the subject of Aerial Locomotion, by M. de Lucy, Paris.