Again, we recognize in the conventional form of angels a total absence of knowledge of natural history, of gravity, of force, &c. Let us, for example, imagine for a moment that the metaphorical wings are real ones used in flight. We see directly that they will only raise the individual perpendicularly into the air. The angelic human creature, even if his wings were--as they ought to do--to replace his arms, would still lack a tail, to use as a rudder to direct his flight. It is clear, then, that no one has seen an angel, and that those who have pretended to have done so, were deeply ignorant men. To make our observations upon this point somewhat more comprehensible, we may just refer to the fact that many individuals, misled apparently by the mass of ideal celestial men--or angels--which are to be seen in almost every cathedral or parish church in Europe, have conceived the idea that they could fly, if only they could contrive the necessary apparatus to append to their arms, legs, or both; in other words, many men have fancied that they could do better for themselves than nature has done for them. But a few minutes' calm thought would teach any one familiar with the composition of forces, that an attempt at the imitation of a bird's flight must be a failure in man. Let me show this by a simple observation: A bird extends its wings, and by a strong stroke towards its own body, rises into the air, though neither solid nor rigid, both wings and air have apparently been so. In imitation of this bird, we will now suppose that a man places himself, with arms outspread, like the letter T between two uprights, forming something like the letter U.
The individual would then be represented thus [J]--unlike the bird, his _point d' appui_ would be solid, and his arms would be far more unyielding than feathers. Yet not one athlete in a million could spring upwards, so as to stand upon the summit of the U. Man's "pectoral muscles"--as physiologists call the mass of flesh below the collar bone and above the nipple--are intended to move the arm; the bird's pectoral muscles are intended to move the body. Cut off a man's arms and pectorals--the counterpart of the bird's wings and fleshy breast--and he has barely lost a tenth part of his weight; on the other hand, cut off the corresponding parts of a bird, i.e.t the pinions and the muscles which move them, and not a tenth part of the original weight is left behind. Speaking coarsely, we may then affirm that man's body is relatively about a hundred times heavier--air being the standard--than that of a bird, and his pectoral muscles, relatively to his body, a hundred times less in bulk. Consequently, even if a human being could, by muscular action, develop the bulk of his "pectorals," so that they should be relatively to the rest of his frame, equal to those of a bird, still his bulk would be so much more solid than that of the bird's bones, flesh, and feathers, that his power of flight would be a hundred times less. A man, with the exception of his lungs, is in health, solid or fluid, in every part of him; a bird's bones, on the contrary, are everywhere permeated by air cavities, which make them as light as pith or cotton wool. A pound of lead and a pound of feathers are certainly equal in weight, yet, if both are allowed to drop from a balloon, the first will reach the ground a long time before the second. In like manner, by contrivance, I could with my breath sustain an ounce of eiderdown in the air, although I am quite powerless to sustain, by like means, the same quantity of solid meat. I say nothing of the relative position of the shoulder-joint in man and birds--although the point is physiologically important.