"I was walking up and down, sad and out of spirits as one always is after a great hope disappointed, when, raising my eyes, I perceived a flight of cranes passing over my head. I stopped to have a good look at them. They were advancing in triangular order, like the English column at the battle of Fontenoy. I saw them traverse the sky from cloud to cloud.--Ah! how well they fly, said I to myself. With what assurance they seem to glide along the viewless path which they follow.--Shall I confess it? alas! may I be forgiven! the horrible feeling of envy for once, once only, entered my heart, and it was for the cranes. I pursued them, with jealous gaze, to the boundaries of the horizon. For a long while afterwards, motionless in the midst of the crowd which was moving about me, I kept observing the rapid movement of the swallows, and I was astonished to see them suspended in the air, just as if I had never before seen that phenomenon. A feeling of profound admiration, unknown to me till then, lighted up my soul. I seemed to myself to be looking upon nature for the first time. I heard with surprise the buzzing of the flies, the song of the birds, and that mysterious and confused noise of the living creation which involuntarily celebrates its Author. Ineffable concert, to which man alone has the sublime privilege of adding the accents of gratitude! Who is the author of this brilliant mechanism? I exclaimed in the transport which animated me. Who is He that, opening his creative hand, let fly the first swallow into the air? It is He who gave commandment to these trees to come forth from the ground, and to lift their branches toward the sky!" Here is a charming page, and containing, though apparently trivial in style, a good and sound philosophy. Let us translate this delightful description into the heavier language of science.