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.