1 The EphemerÆ in the larva and pupa state reside in the water concealed during the day under stones or in horizontal burrows which they form in the banks. Although resembling the perfect insect in several respects, they differ materially in having longer antennÆ, in wanting ocelli, and in possessing horn-like mandibles; the abdomen has, moreover, on each side a row of plates, mostly in pairs, which are a kind of false branchiÆ, and which are employed not only in respiration, but also as paddles.—Cuvier’s Animal Kingdom, p.576. London, 1840.

2 Kirby and Spence observe that some insects which are not naturally aquatic, do, nevertheless, swim very well if they fall into the water. They instance a kind of grasshopper (Acrydium), which can paddle itself across a stream with great rapidity by the powerful strokes of its hind legs.—(Introduction to Entomology, 5th edit., 1828, p.360.) Nor should the remarkable discovery by Sir John Lubbock of a swimming insect (Polynema natans), which uses its wings exclusively as fins, be overlooked.—Linn. Trans. vol. xxiv. p.135.

3 This is also true of quadrupeds. It is the posterior part of the feet which is set down first.

4 “According to Sainbell, the celebrated horse Eclipse, when galloping at liberty, and with its greatest speed, passed over the space of twenty-five feet at each stride, which he repeated 2 1/3 times in a second, being nearly four miles in six minutes and two seconds. The race-horse Flying Childers was computed to have passed over eighty-two feet and a half in a second, or nearly a mile in a minute.”

5 A portion of the timbers, etc., of one of Her Majesty’s ships, having the tusk of a sword-fish imbedded in it, is to be seen in the Hunterian Museum of the Royal College of Surgeons of England.

6 A flying creature exerts its greatest power when rising. The effort is of short duration, and inaugurates rather than perpetuates flight. If the volant animal can launch into space from a height, the preliminary effort may be dispensed with as in this case, the weight of the animal acting upon the inclined planes formed by the wings gets up the initial velocity.

7 “On the various modes of Flight in relation to AËronautics.”—Proceedings of the Royal Institution of Great Britain, March 22, 1867.

8 “On the Mechanical Appliances by which Flight is attained in the Animal Kingdom.”—Transactions of the Linnean Society, vol.xxvi.

9 “On the Physiology of Wings.”—Transactions of the Royal Society of Edinburgh, vol.xxvi.

10 Cyc. of Anat. and Phy., Art. “Motion,” by John Bishop, Esq.

11 Bishop, op. cit.

12 Bishop, op. cit.

13 Bishop, op. cit.

14 “Lectures on the Physiology of the Circulation in Plants, in the Lower Animals, and in Man.”—Edinburgh Medical Journal for January and February 1873.

15 Muscles virtually possess a pulling and pushing power; the pushing power being feeble and obscured by the flaccidity of the muscular mass. In order to push effectually, the pushing substance must be more or less rigid.

16 The extensor muscles preponderate in mass and weight over the flexors, but this is readily accounted for by the fact, that the extensors, when limbs are to be straightened, always work at a mechanical disadvantage. This is owing to the shape of the bones, the conformation of the joints, and the position occupied by the extensors.

17 “On the Arrangement of the Muscular Fibres in the Ventricles of the Vertebrate Heart, with Physiological Remarks,” by the Author.—Philosophical Transactions, 1864.

“On the Muscular Arrangements of the Bladder and Prostate, and the manner in which the Ureters and Urethra are closed,” by the Author.—Philosophical Transactions, 1867.

“On the Muscular Tunics in the Stomach of Man and other Mammalia,” by the Author.—Proceedings Royal Society of London, 1867.

18 Lectures “On the Physiology of the Circulation in Plants, in the Lower Animals, and in Man,” by the Author.—Edinburgh Medical Journal for September 1872.

19 That the movements of the extremities primarily emanate from the spine is rendered probable by the remarkable powers possessed by serpents. “It is true,” writes Professor Owen (op. cit. p.261), “that the serpent has no limbs, yet it can outclimb the monkey, outswim the fish, outleap the jerboa, and, suddenly loosing the close coils of its crouching spiral, it can spring into the air and seize the bird upon the wing.” ... “The serpent has neither hands nor talons, yet it can outwrestle the athlete, and crush the tiger in the embrace of its ponderous overlapping folds.” The peculiar endowments, which accompany the possession of extremities, it appears to me, present themselves in an undeveloped or latent form in the trunk of the reptile.

20 The Vampire Bat of the Island of Bonin, according to Dr. Buckland, can also swim; and this authority was of opinion that the Pterodactyle enjoyed similar advantages.—Eng. Cycl. vol.iv. p.495.

21 Comp. Anat. and Phys. of Vertebrates, by Professor Owen, vol.i. pp. 262, 263. Lond. 1866.

22 The jerboa when pursued can leap a distance of nine feet, and repeat the leaps so rapidly that it cannot be overtaken even by the aid of a swift horse. The bullfrog, a much smaller animal, can, when pressed, clear from six to eight feet at each bound, and project itself over a fence five feet high.

23 The long, powerful tail of the kangaroo assists in maintaining the equilibrium of the animal prior to the leaps; the posterior extremities and tail forming a tripod of support.

24 The rabbit occasionally takes several short steps with the fore legs and one long one with the hind legs; so that it walks with the fore legs, and leaps with the hind ones.

25 If a cat when walking is seen from above, a continuous wave of movement is observed travelling along its spine from before backwards. This movement closely resembles the crawling of the serpent and the swimming of the eel.

26 “On the Breeding of Hunters and Roadsters.” Prize Essay.—Journal of Royal Agricultural Society for 1863.

27 Gamgee in Journal of Anatomy and Physiology, vol.iii. pp.375, 376.

28 The woodpeckers climb by the aid of the stiff feathers of their tails; the legs and tail forming a firm basis of support.

29 In this order there are certain birds—the sparrows and thrushes, for example—which advance by a series of vigorous leaps; the leaps being of an intermitting character.

30 The toes in the emu amount to three.

31 Feet designed for swimming, grasping trees, or securing prey, do not operate to advantage on a flat surface. The awkward waddle of the swan, parrot, and eagle when on the ground affords illustrations.

32 In draught horses the legs are much wider apart than in racers; the legs of the deer being less widely set than those of the racer.

33 In the apteryx the wings are so very small that the bird is commonly spoken of as the “wingless bird.”

34 “The posterior extremities in both the lion and tiger are longer, and the bones inclined more obliquely to each other than the anterior, giving them greater power and elasticity in springing.”

35 “The pelvis receives the whole weight of the trunk and superposed organs, and transmits it to the heads of the femurs.”

36 The spreading action of the toes is seen to perfection in children. It is more or less destroyed in adults from a faulty principle in boot and shoemaking, the soles being invariably too narrow.

37 The brothers Weber found that so long as the muscles exert the general force necessary to execute locomotion, the velocity depends on the size of the legs and on external forces, but not on the strength of the muscles.

38 “In quick walking and running the swinging leg never passes beyond the vertical which cuts the head of the femur.”

39 “The number of steps which a person can take in a given time in walking depends, first, on the length of the leg, which, governed by the laws of the pendulum, swings from behind forwards; secondly, on the earlier or later interruption which the leg experiences in its arc of oscillation by being placed on the ground. The weight of the swinging leg and the velocity of the trunk serve to give the impulse by which the foot attains a position vertical to the head of the thigh-bone; but as the latter, according to the laws of the pendulum, requires in the quickest walking a given time to attain that position, or half its entire curve of oscillation, it follows that every person has a certain measure for his steps, and a certain number of steps in a given time, which, in his natural gait in walking, he cannot exceed.”

40 Cyc. of Anat. and Phy., article “Motion.”

41 The lepidosiren is furnished with two tapering flexible stem-like bodies, which depend from the anterior ventral aspect of the animal, the siren having in the same region two pairs of rudimentary limbs furnished with four imperfect toes, while the proteus has anterior extremities armed with three toes each, and a very feeble posterior extremity terminating in two toes.

42 Borelli, “De motu Animalium,” plate 4, fig.5, sm. 4to, 2 vols. RomÆ, 1680.

43 It is only when a fish is turning that it forces its body into a single curve.

44 The Syngnathi, or Pipefishes, swim chiefly by the undulating movement of the dorsal fin.

45 If the pectoral fins are to be regarded as the homologues of the anterior extremities (which they unquestionably are), it is not surprising that in them the spiral rotatory movements which are traceable in the extremities of quadrupeds, and so fully developed in the wings of bats and birds, should be clearly foreshadowed. “The muscles of the pectoral fins,” remarks Professor Owen, “though, when compared with those of the homologous members in higher vertebrates, they are very small, few, and simple, yet suffice for all the requisite movements of the fins—elevating, depressing, advancing, and again laying them prone and flat, by an oblique stroke, upon the sides of the body. The rays or digits of both pectorals and ventrals (the homologues of the posterior extremities) can be divaricated and approximated, and the intervening webs spread out or folded up.”—Op. cit. vol.i. p.252.

46 Vide “Remarks on the Swimming of the Cetaceans,” by Dr. Murie, Proc. Zool. Soc., 1865, pp.209, 210.

47 In a few instances the caudal fin of the fish, as has been already stated, is more or less pressed together during the back stroke, the compression and tilting or twisting of the tail taking place synchronously.

48 The unusual opportunities afforded by this unrivalled collection have enabled me to determine with considerable accuracy the movements of the various land-animals, as well as the motions of the wings and feet of birds, both in and out of the water. I have also studied under the most favourable circumstances the movements of the otter, sea-bear, seal, walrus, porpoise, turtle, triton, crocodile, frog, lepidosiren, proteus, axolotl, and the several orders of fishes.

49 This is the reverse of what takes place in flying, the anterior or thick margins of the wings being invariably directed upwards.

50 The air-bladder is wanting in the dermopteri, plagiostomi, and pleuronectidÆ.—Owen, op. cit. p.255.

51 The frog in swimming leisurely frequently causes its extremities to move diagonally and alternately. When, however, pursued and alarmed, it folds its fore legs, and causes its hind ones to move simultaneously and with great vigour by a series of sudden jerks, similar to those made by man when swimming on his back.

52 The professional swimmer avoids bobbing, and rests the side of his head on the water to diminish its weight and increase speed.

53 The greater power possessed by the limbs during extension, and more especially towards the end of extension, is well illustrated by the kick of the horse; the hind feet dealing a terrible blow when they have reached their maximum distance from the body. Ostlers are well aware of this fact, and in grooming a horse keep always very close to his hind quarters, so that if he does throw up they are forced back but not injured.

54 The outward direction given to the arm and hand enables them to force away the back water from the body and limbs, and so reduce the friction to forward motion.

55 History of British Birds, vol.i. p.48.

56 The guillemots in diving do not use their feet; so that they literally fly under the water. Their wings for this purpose are reduced to the smallest possible dimensions consistent with flight. The loons, on the other hand, while they employ their feet, rarely, if ever, use their wings. The subaqueous progression of the grebe resembles that of the frog.—Cuvier’s Animal Kingdom, Lond. 1840, pp.252, 253.

57 In the swimming of the crocodile, turtle, triton, and frog, the concave surfaces of the feet of the anterior extremities are likewise turned backwards.

58 The effective stroke is also delivered during flexion in the shrimp, prawn, and lobster.

59 “On the Various Modes of Flight in relation to AËronautics.” By the Author.—Proceedings of the Royal Institution of Great Britain, March 1867.

60 Nature and Art, November 1866, p.173.

61 In this form of lever the power is applied between the fulcrum and the weight to be raised. The mass to be elevated is the body of the insect, bat, or bird,—the force which resides in the living pinion (aided by the inertia of the trunk) representing the power, and the air the fulcrum.

62 In some cases the posterior margin is slightly elevated above the horizon (fig.53, g).

63 Weight, as is well known, is the sole moving power in the clock—the pendulum being used merely to regulate the movements produced by the descent of the leads. In watches, the onus of motion is thrown upon a spiral spring; and it is worthy of remark that the mechanician has seized upon, and ingeniously utilized, two forces largely employed in the animal kingdom.

64 Sappey enumerates fifteen air-sacs,—the thoracic, situated at the lower part of the neck, behind the sternum; two cervical, which run the whole length of the neck to the head, which they supply with air; two pairs of anterior, and two pairs of posterior diaphragmatic; and two pairs of abdominal.

65 “On the Functions of the Air-cells and the Mechanism of Respiration in Birds,” by W.H. Drosier, M.D., Caius College.—Proc. Camb. Phil. Soc., Feb. 12, 1866.

66 “An Account of certain Receptacles of Air in Birds which communicate with the Lungs, and are lodged among the Fleshy Parts and in the Hollow Bones of these Animals.”—Phil. Trans., Lond. 1774.

67 According to Dr. Crisp the swallow, martin, snipe, and many birds of passage have no air in their bones (Proc. Zool. Soc., Lond. part xxv. 1857, p. 13). The same author, in a second communication (pp.215 and 216), adds that the glossy starling, spotted flycatcher, whin-chat, wood-wren, willow-wren, black-headed bunting, and canary, five of which are birds of passage, have likewise no air in their bones. The following is Dr. Crisp’s summary:—Out of ninety-two birds examined he found “air in many of the bones, five (FalconidÆ); air in the humeri and not in the inferior extremities, thirty-nine; no air in the extremities and probably none in the other bones, forty-eight.”

68 Nearly allied to this is the great gular pouch of the bustard. Specimens of the air-sac in the orang, emu, and bustard, and likewise of the air-sacs of the swan and goose, as prepared by me, may be seen in the Museum of the Royal College of Surgeons of England.

69 In this diagram I have purposely represented the right wing by a straight rigid rod. The natural wing, however, is curved, flexible, and elastic. It likewise moves in curves, the curves being most marked towards the end of the up and down strokes, as shown at m n, o p. The curves, which are double figure-of-8 curves, are obliterated towards the middle of the strokes (a r). This remark holds true of all natural wings, and of all artificial wings properly constructed. The curves and the reversal thereof are necessary to give continuity of motion to the wing during its vibrations, and what is not less important, to enable the wing alternately to seize and dismiss the air.

70 In birds which skim, sail, or glide, the pinion is greatly elongated or ribbon-shaped, and the weight of the body is made to operate upon the inclined planes formed by the wings, in such a manner that the bird when it has once got fairly under weigh, is in a measure self-supporting. This is especially the case when it is proceeding against a slight breeze—the wind and the inclined planes resulting from the upward inclination of the wings reacting upon each other, with this very remarkable result, that the mass of the bird moves steadily forwards in a more or less horizontal direction.

71 “On the Physiology of Wings, being an Analysis of the Movements by which Flight is produced in the Insect, Bat, and Bird.”—Trans. Roy. Soc. of Edinburgh, vol.xxvi.

72 “On the Flight of Birds, of Bats, and of Insects, in reference to the subject of AËrial Locomotion,” by M. de Lucy, Paris.

73 M. de Lucy, op. cit.

74 The grebes among birds, and the beetles among insects, furnish examples where small wings, made to vibrate at high speeds, are capable of elevating great weights.

75 “The wing is short, broad, convex, and rounded in grouse, partridges, and other rasores; long, broad, straight, and pointed in most pigeons. In the peregrine falcon it is acuminate, the second quill being longest, and the first little shorter; and in the swallows this is still more the case, the first quill being the longest, the rest rapidly diminishing in length.”—Macgillivray, Hist. Brit. Birds, vol.i. p.82. “The hawks have been classed as noble or ignoble, according to the length and sharpness of their wings; and the falcons, or long-winged hawks, are distinguished from the short-winged ones by the second feather of the wing being either the longest or equal in length to the third, and by the nature of the stoop made in pursuit of their prey.”—Falconry in the British Isles, by F.H. Salvin and W. Brodrick. Lond. 1855, p. 28.

76 The degree of valvular action varies according to circumstances.

77 Of this circle, the thorax may be regarded as forming the centre, the abdomen, which is always heavier than the head, tilting the body slightly in an upward direction. This tilting of the trunk favours flight by causing the body to act after the manner of a kite.

78 I have frequently timed the beats of the wings of the Common Heron (Ardea cinerea) in a heronry at Warren Point. In March 1869 I was placed under unusually favourable circumstances for obtaining trustworthy results. I timed one bird high up over a lake in the vicinity of the heronry for fifty seconds, and found that in that period it made fifty down and fifty up strokes; i.e. one down and one up stroke per second. I timed another one in the heronry itself. It was snowing at the time (March 1869), but the birds, notwithstanding the inclemency of the weather and the early time of the year, were actively engaged in hatching, and required to be driven from their nests on the top of the larch trees by knocking against the trunks thereof with large sticks. One unusually anxious mother refused to leave the immediate neighbourhood of the tree containing her tender charge, and circled round and round it right overhead. I timed this bird for ten seconds, and found that she made ten down and ten up strokes; i.e. one down and one up stroke per second precisely as before. I have therefore no hesitation in affirming that the heron, in ordinary flight, makes exactly sixty down and sixty up strokes per minute. The heron, however, like all other birds when pursued or agitated, has the power of greatly augmenting the number of beats made by its wings.

79 The above observation was made at Carlow on the Barrow in October 1867, and the account of it is taken from my note-book.

80 It happens occasionally in insects that the posterior margin of the wing is on a higher level than the anterior one towards the termination of the up stroke. In such cases the posterior margin is suddenly rotated in a downward and forward direction at the beginning of the down stroke—the downward and forward rotation securing additional elevating power for the wing. The posterior margin of the wing in bats and birds, unless they are flying downwards, never rises above the anterior one, either during the up or down stroke.

81 That the elytra take part in flight is proved by this, that when they are removed, flight is in many cases destroyed.

82 The wings of the May-fly are folded longitudinally and transversely, so that they are crumpled up into little squares.

83 Kirby and Spence, vol.ii. 5th ed., p.352.

84 The furcula are usually united to the anterior part of the sternum by ligament; but in birds of powerful flight, where the wings are habitually extended for gliding and sailing, as in the frigate-bird, the union is osseous in its nature. “In the frigate-bird the furcula are likewise anchylosed with the coracoid bones.”—Comp. Anat. and Phys. of Vertebrates, by Prof. Owen, vol.ii. p.66.

85 “The os humeri, or bone of the arm, is articulated by a small rounded surface to a corresponding cavity formed between the coracoid bone and the scapula, in such a manner as to allow great freedom of motion.”—Macgillivray’s Brit. Birds, vol.i. p.33.

“The arm is articulated to the trunk by a ball-and-socket joint, permitting all the freedom of motion necessary for flight.”—Cyc. of Anat. and Phys., vol.iii. p.424.

86 Chabrier, as rendered by E.F. Bennett, F.L.S., etc.

87 Linn. Trans. vii. p.40.

88 Vol.iii. p.36.

89 “The hobby falcon, which abounds in Bulgaria during the summer months, hawks large dragonflies, which it seizes with the foot and devours whilst in the air. It also kills swifts, larks, turtle-doves, and bee-birds, although more rarely.”—Falconry in the British Isles, by Francis Henry Salvin and William Brodrick. Lond. 1855.

90 One of the best descriptions of the bones and muscles of the bird is that given by Mr. Macgillivray in his very admirable, voluminous, and entertaining work, entitled History of British Birds. Lond. 1837.

91 Mr. Macgillivray and C.J.L. Krarup, a Danish author, state that the wing is elevated by a vital force, viz. by the contraction of the pectoralis minor. This muscle, according to Krarup, acts with one-eighth the intensity of the pectoralis major (the depressor of the wing). He bases his statement upon the fact that in the pigeon the pectoralis minor or elevator of the wing weighs one-eighth of an ounce, whereas the pectoralis major or depressor of the wing weighs seven-eighths of an ounce. It ought, however, to be borne in mind that the volume of a muscle does not necessarily determine the precise influence exerted by its action; for the tendon of the muscle may be made to act upon a long lever, and, under favourable conditions, for developing its powers, while that of another muscle may be made to act upon a short lever, and, consequently, under unfavourable conditions.—On the Flight of Birds, p. 30. Copenhagen, 1869.

92 A careful account of the musculo-elastic structures occurring in the wing of the pigeon is given by Mr. Macgillivray in his History of British Birds, pp. 37, 38.

93 “The humerus varies extremely in length, being very short in the swallow, of moderate length in the gallinaceous birds, longer in the crows, very long in the gannets, and unusually elongated in the albatross. In the golden eagle it is also seen to be of great length.”—Macgillivray’s British Birds, vol.i. p.30.

94 Prevailing Opinions as to the Direction of the Down Stroke.—Mr. Macgillivray, in his History of British Birds, published in 1837, states (p.34) that in flexion the wing is drawn upwards, forwards, and inwards, but that during extension, when the effective stroke is given, it is made to strike outwards, downwards, and backwards. The Duke of Argyll holds a similar opinion. In speaking of the hovering of birds, he asserts that “if a bird, by altering the axis of its own body, can direct its wing stroke in some degree forwards, it will have the effect of stopping instead of promoting progression;” and that, “Except for the purpose of arresting their flight, birds can never strike except directly downwards—that is, directly against the opposing force of gravity.”—Good Words, Feb. 1865, p. 132.

Mr. Bishop, in the Cyc. of Anat. and Phys., vol.iii. p.425, says, “In consequence of the planes of the wings being disposed either perpendicularly or obliquely backwards to the direction of their motion, a corresponding impulse is given to their centre of gravity.” Professor Owen, in like manner, avers that “a downward stroke would only tend to raise the bird in the air; to carry it forwards, the wings require to be moved in an oblique plane, so as to strike backwards as well as downwards.”—Comp. Anat. and Phys. of Vertebrates, vol.ii. p.115.

The following is the account given by M.E. Liais:—“When a bird is about to depress its wing, this is a little inclined from before backwards. When the descending movement commences, the wing does not descend parallel to itself in a direction from before backwards; but the movement is accompanied by a rotation of several degrees round the anterior edge, so that the wing becomes more in front than behind, and the descending movement is transferred more and more backwards.... When the wing has completely descended, it is both further back and lower than at the commencement of the movement.”—“On the Flight of Birds and Insects.” Annals of Nat. Hist. vol.xv. 3d series, p.156.

95 The average weight of the albatross, as given by Gould, is 17 lbs.—Ibis, 2d series, vol.i. 1865, p.295.

96 “On some of the Birds inhabiting the Southern Ocean,” by Capt. F.W. Hutton.—Ibis, 2d series, vol.i. 1865, p.282.

97 Advantages possessed by long Pinions.—The long narrow wings are most effective as elevators and propellers, from the fact (pointed out by Mr. Wenham) that at high speeds, with very oblique incidences, the supporting effect becomes transferred to the front edge of the pinion. It is in this way “that the effective propelling area of the two-bladed screw is tantamount to its entire circle of revolution.” A similar principle was announced by Sir George Cayley upwards of fifty years ago. “In very acute angles with the current, it appears that the centre of resistance in the sail does not coincide with the centre of its surface, but is considerably in front of it. As the obliquity of the current decreases, these centres approach, and coincide when the current becomes perpendicular to the plane; hence any heel of the machine backwards or forwards removes the centre of support behind or before the point of suspension.”—Nicholson’s Journal, vol.xxv. p.83. When the speed attained by the bird is greatly accelerated, and the stratum of air passed over in any given time enormously increased, the support afforded by the air to the inclined planes formed by the wings is likewise augmented. This is proved by the rapid flight of skimming or sailing birds when the wings are moved at long intervals and very leisurely. The same principle supports the skater as he rushes impetuously over insecure ice, and the thin flat stone projected along the surface of still water. The velocity of the movement in either case prevents sinking by not giving the supporting particles time to separate.

98 “On some of the Birds inhabiting the Southern Ocean.”—Ibis, 2d series, vol.i. 1865.

99 Professor Wilson’s Sonnet, “A Cloud,” etc.

100 “If the albatross desires to turn to the right he bends his head and tail slightly upwards, at the same time raising his left side and wing, and lowering the right in proportion to the sharpness of the curve he wishes to make, the wings being kept quite rigid the whole time. To such an extent does he do this, that in sweeping round, his wings are often pointed in a direction nearly perpendicular to the sea; and this position of the wings, more or less inclined to the horizon, is seen always and only when the bird is turning.”—“On some of the Birds inhabiting the Southern Ocean.” Ibis, 2d series, vol.i. 1865, p. 227.

101 The heron is in the habit, when pursued by the falcon, of disgorging the contents of his crop in order to reduce his weight.

102 The condor, on some occasions, attains an altitude of six miles.

103 “AËrial Locomotion,” by F.H. Wenham.—World of Science, June 1867.

104 Mr. Stringfellow stated that his machine occasionally left the wire, and was sustained by its superimposed planes alone.

105 Report on the First Exhibition of the AËronautical Society of Great Britain, held at the Crystal Palace, London, in June 1868, p.10.

106 Mons. Nadar, in a paper written in 1863, enters very fully into the subject of artificial flight, as performed by the aid of the screw. Liberal extracts are given from Nadar’s paper in Astra Castra, by Captain Hatton Turner. London, 1865, p.340. To Turner’s handsome volume the reader is referred for much curious and interesting information on the subject of AËrostation.

107 Borelli, De Motu Animalium. Sm. 4to, 2 vols. RomÆ, 1680.

108 De Motu Animalium, Lugduni Batavorum apud Petrum Vander. Anno MDCLXXXV. Tab. XIII. figure 2. (New edition.)

109 Revue des Cours Scientifiques de la France et de l’Etranger. Mars 1869.

110 It is clear from the above that Borelli did not know that the wings of birds strike forwards as well as downwards during the down stroke, and forwards as well as upwards during the up stroke. These points, as well as the twisting and untwisting figure-of-8 action of the wing, were first described by the author. Borelli seems to have been equally ignorant of the fact that the wings of insects vibrate in a more or less horizontal direction.

111 “Reign of Law”—Good Words, 1865.

112 “Reign of Law”—Good Words, February 1865, p.128.

113 History of British Birds. Lond. 1837, p.43.

114 “MÉchanisme du vol chez les insectes. Comment se fait la propulsion,” by Professor E.J. Marey. Revue des Cours Scientifiques de la France et de l’Etranger, for 20th March 1869, p.254.

115 Revue des Cours Scientifiques de la France et de l’Etranger. 8vo. March 20, 1869.

116 In sculling strictly speaking, it is the upper surface of the oar which is most effective; whereas in flying it is the under.

117 Compare Marey’s description with that of Borelli, a translation of which I subjoin. “Let a bird be suspended in the air with its wings expanded, and first let the under surfaces (of the wings) be struck by the air ascending perpendicularly to the horizon with such a force that the bird gliding down is prevented from falling: I say that it (the bird) will be impelled with a horizontal forward motion, because the two osseous rods of the wings are able, owing to the strength of the muscles, and because of their hardness, to resist the force of the air, and therefore to retain the same form (literally extent, expansion), but the total breadth of the fan of each wing yields to the impulse of the air when the flexible feathers are permitted to rotate around the manubria or osseous axes, and hence it is necessary that the extremities of the wings approximate each other: wherefore the wings acquire the form of a wedge whose point is directed towards the tail of the bird, but whose surfaces are compressed on either side by the ascending air in such a manner that it is driven out in the direction of its base. Since, however, the wedge formed by the wings cannot move forward unless it carry the body of the bird along with it, it is evident that it (the wedge) gives place to the air impelling it, and therefore the bird flies forward in a horizontal direction. But now let the substratum of still air be struck by the fans (feathers) of the wings with a motion perpendicular to the horizon. Since the fans and sails of the wings acquire the form of a wedge, the point of which is turned towards the tail (of the bird), and since they suffer the same force and compression from the air, whether the vibrating wings strike the undisturbed air beneath, or whether, on the other hand, the expanded wings (the osseous axes remaining rigid) receive the percussion of the ascending air; in either case the flexible feathers yield to the impulse, and hence approximate each other, and thus the bird moves in a forward direction.”—De Motu Animalium, pars prima, prop. 196, 1685.

118 The human wrist is so formed that if a wing be held in the hand at an upward angle of 45°, the hand can apply it to the air in a vertical or horizontal direction without difficulty. This arises from the power which the hand has of moving in an upward and downward direction, and from side to side with equal facility. The hand can also rotate on its long axis, so that it virtually represents all the movements of the wing at its root.

119 The artificial currents produced by the wing during its descent may be readily seen by partially filling a chamber with steam, smoke, or some impalpable white powder, and causing the wing to descend in its midst. By a little practice, the eye will not fail to detect the currents represented at d, e, f, g, h, i, l, m, o, p, q, r of fig.129, p.253.