SlTTEMBKR 2 1, 1^92 ^ 



NA TURE 



501 



But why should not man fiy ? It is not that he does not desire 

 to do so. For every denizen of our precarious British climate, 

 wlien he has noticed the ease with which swallows and other 

 migratory birds fly off on the approach of winter, hundreds and 

 even thousands ot miles to the sunny south, must have wished 

 he could do the same. One reason why we cannot fly, even 

 with arlilicial aids, such as wings, is that, as in the case of the 

 penguin or the ostrich, our bodily mechanism is specialised and 

 our muscular power diffused in other directions, so that we could 

 not actuate wings of sufficient area to carry us even if we had 

 them. 



M. de Lucy, a French naturalist, has shown that the wing- 

 area of flying animals varies from about 49 square feet per lb. 

 of weight in the gnat, and 5 square feet in the swallow, to half 

 a square foot per lb. of weight in the Australian crane, which 

 weighs 21 lbs. and yet flies well. If he were to adopt the last 

 -or smallest proportion, a man weighing 12 stone would require 

 a pair of wings each of them 14 feet long by 3 feet broad, or 

 double the area of an ordinary room door, to carry him, with- 

 out taking into account the weight of the wings themselves. 



In flying birds there is a strong tripod arrangement to secure 

 firm points of attachment for the wings, and a deep keel in the 

 breast-bone, to which the large pectoral muscles are secured. 

 Think of the wings I have described and the absence of pivots, 

 keel, and muscles in man, and it will be tolerably obvious why 

 'he cannot fly, even with artificial wings. 



But it might be contended that a man's strength is in his legs 

 rather than in his arms, and that it is conceivable that a success- 

 ful flying-apparatus might be made if adapted for the most, 

 iistead of the least, favourable application of his bodily strength. 



According to D. K. Clark ("Rules, Tables, and Data," 

 pp. 719 3nd 720), a labourer working all day exerts on an 

 average '13 horse-power. The maximum power of a very strong 

 man for a very shi-irt time is '46 horse-power. 



According to Dr. Houghton ("Animal Mechanics"), the 

 oarsmen in a boat-race of i mile, rowed in 7 minutes, exerted 

 each '26 horse-power. 



Suppose we take the rowing case as the maximum maintain- 

 able for, say, 7 minutes, by a man weighing 168 lbs. Then in 

 flight he would have to sustain a weight ol 



1^-^ = 646 lbs. 

 •26 



per horse-power exerted, besides the weight of the apparatus. 



Now, we shall find later that no birds support even half 

 that weight per horse-power which they have the power 

 to exert, and that recent aeroplane experiments prove its 

 impossibility. On the ground, therefore, that he is too heavy 

 in proportion to his strength, it is clear that man is unfitted for 

 flight, as well as because his limbs are not adapted for it. 



It does not follow, however, that by aid of mechanisms apart 

 from his own body, and worked by power independent of his 

 own strength, man may not imitate, compete with, and even 

 outdo the fowls of the air. 



Let us consider a few facts showing what birds can do. A 

 gannet hovers in the air above the sea. Suddenly he nearly 

 closes his wings, swoops down, and with a splash disappears 

 below the .surface. Shortly after he reappears with a fish in 

 his mouth, which he swallows in a few gulps ; then, after 

 swimming on the surface a little, he reascends into the air to 

 repeat the operation. 



The swallow rises into the air with a few rapid movements 

 of the wings, then slides down as though on an aiirial switch- 

 back, and I hen up again tilt he nearly reaches his original 

 •Iieight, or he circles round by raising one wing, like a runner 

 rounding a curve. 



Ihe condor vulture, which measures sometimes 15 feet across 

 the wings, will fly upwards till quite out of sight. 



A flock of cranes have been seen migrating at a height of three 

 miles, and proceeding apparently without any movement of the 

 wings. 



The peregrine falcon will swoop down upon a partridge, and, 

 missing it by a doubling movement of the latter, will slide up- 

 wards, thus converting his kinetic into new potential energy. 

 He will then turn and descend again, this time securing his 

 ,prey. 



Mr. J. E. llarting, one of the principal British ornith'.logical 

 authorities, has, after careful investigation, arrived at the con- 

 clusion that the speed of falcons in lull flight is about 60 miles 

 per hour. {Field, December 5, 1891, p. 856). 



Mr. W. B. Tegetmeier, another well-known authority, gives 

 {Field, January 22, 1SS7, p. 114) the results of a number of ex- 

 periments on the speed of homing pigeons, made under the 

 auspices of the United Counties Flying Club in 18S3. The 

 average speed of the winner in eighteen races was 36 miles, and 

 the maximum 55 miles per hour. The greatest distance flown 

 was 309 miles. 



The albatross, the largest web- fooled bird, measuring some- 

 times 1 7 feet from tip to tip of wing, and weighing up to 20 lbs. , 

 frequently accompanies ocean steamers from the Cape to Mel- 

 bourne, a distance of 5,500 knots, without being seen to rest on 

 the way. 



An American naturalist, Mr. J. Lancaster, who spent no less 

 than five years on the west coast of Florida (" Problem of the 

 Soaring Bird," ^OTfnVrtK A'iT/K?'3/«jV, 18S5, pp. 1055-1162), in 

 order to study the habits of aquatic and other birds which 

 frequent these shores, arrived at the following conclusions, 

 viz. ; — 



Though all birds move their wings sometimes, many can re- 

 main indefinitely in the air, with wings extended and motionIes=, 

 and either with or without forv\ard movement. This he calls 

 " soaring." 



The wing-area of soaring birds varies from i to above 2 square 

 feet per lb. of weight. 



The larger the wings per lb. of weight the greater the power 

 to soar. 



The heavier the bird the steadier his movements. 



Soaring birds always face the wind, which, if they do not 

 move forward or downward, must rot blow at a less speed thin 

 2 to 5 miles per hour. 



Mr. Lancaster specially watched a flock of buzzards about 

 30 feet above his head, waiting for him to leave the body of a 

 dead porpoise. Their wings were about 8 feet from tip to tip, 

 and their average weight about 6 lbs. During three hours at 

 mid-day, when the wind which they faced was very strong, 

 they flapped their wings about twenty limes each. Later, 

 during two hours, when the wind had subsided, they never 

 moved them at all. 



Mr. Lancaster timed frigate birds, and found them able to go 

 at the rate of 100 miles per hour, and that on fixed wings ; he 

 is of opinion that at all events up to that speed they can dy 

 just as fast as they please. He says, further, that the same 

 birds can live in the air a week at a time, night and day, with- 

 out touching a roost, and that buzzards, cranes, and gannets 

 can do the same for several hours at a time. 



The observed facts relating to the phenomena of flight are 

 still but very imperfectly understood. That a bird should be 

 able to maintain a downward pressure on the air sufficient to 

 counteract the effect of its own weight, and abackward pressure 

 sufficient to force itself forward at such speeds as I have named, 

 .'eems wonderful enough when it is known that it continuously 

 operates its wings. But that it should be able to do the same 

 without any muscular movement at all is almost incomprehen- 

 sible. It seems to be an instance of the suspension of the laws 

 of gravity and of the existence of cause without effect, and of 

 effect without cause. It is not a case of flotation, like a 

 balloon, for any bird falls to the earth like a stone when shot. 

 Mr. Lancaster suggests that the bird's own weight is the force 

 which enaljles him to counteract the effect thereof, but this 

 explanation is, I confess, beyond ray comprehension. 



It seems to me that for every pound of his weight pressing 

 downwards there must be an equivalent force pressing upwards. 

 This can be produced only by his giving downward motion to 

 the air previously at rest, or by his arresting previous motion of 

 air in an upward direction. The latter alternative involves the 

 supposition that the air-currents which soaring birds face are 

 not, as Mr. Lancaster believe-, always horizontal, but must 

 have, to some extent, an upward direction. If a parachute were 

 falling in a current of air which was moving upwaids at the 

 same rate as the parachute fell, it would obviously retain its 

 level, yet gravity w ould be acting. So, if a bird with extended 

 wings were sliding down a stream of air which was tending up- 

 wards at the same angle and same velocity, the phenomenon of 

 soaring would be produced. 



Wcii^hl of Birds in relalion lo their Bui/;.— It is generally 

 believed that birds are lighter, bulk for bulk, than other animal', 

 and that to this lightness they owe, in some degree, their power 

 of flight and of floating on water. To account for this it is said 

 that their bone-cavities are filled with air, and that some, though 

 not even all, flying birds have small air-sacs under the skin. U 



NO. 1247, VOL. 48] 



