After this, the Empress asked them, what kind of substance or creature the air was? The Bird-men answered, that they could have no other perception of the air, but by their own respiration: For, said they, some bodies are only subject to touch, others only to sight, and others only to smell; but some are subject to none of our exterior senses: For nature is so full of variety, that our weak senses cannot perceive all the various sorts of her creatures; neither is there any one object perceptible by all our senses, no more than several objects are by one sense. I believe you, replied the Empress; but if you can give no account of the air, said she, you will hardly be able to inform me how wind is made; for they say, that wind is nothing but motion of the air. The Bird-men answered, that they observed wind to be more dense than air, and therefore subject to the sense of touch; but what properly wind was, and the manner how it was made, they could not exactly tell; some said, it was caused by the clouds falling on each other; and others, that it was produced of a hot and dry exhalation: which ascending, was driven down again by the coldness of the air that is in the middle region, and by reason of its lightness, could not go directly to the bottom, but was carried by the air up and down: Some would have it a flowing water of the air; and others again, a flowing air moved by the blaze of the stars.