When you breathe on a mirror, the damp of your breath is condensed by the coolness of the glass. A film of mist forms over the mirror. Of an evening you may see the mist lying over the river or meadows; for the sun is gone down and the earth and air are cooling. But the upper air cools more quickly than the lower part, since the latter is still warmed by the heat stored in the earth. So, as the cooler air from above drops down, it acts like a mirror to the breath of the earth or the air that lies close over it; and this air is condensed into mist. All through the night both air and earth are cooling, but the earth more slowly, so that there is still a meeting of cooler and warmer air and consequent condensations, and the mist is hovering over the meadows when the next morning’s sun rises. As the sun mounts up, it begins to spread its warmth and the upper air is the first to feel it. Growing warm, it rises, drawing up after it the cooler air below. And as the cooler air is sucked up, the warmer air closes in behind it; until, as this circulation of cool and warm continues, the warmth at last reaches down to the mists above the earth. And then commences that beautiful sight that you may see on some summer mornings. The mists, that a while ago lay like a blanket over the sleeping earth, begin to stir, as if they themselves were awakening from sleep. They tremble a little, then slowly stretch themselves, and begin to rise to meet the warmth of day. And as they rise, little wisps of mist become detached from the main body and float up and disappear, until gradually the whole rising mass is rent asunder by the currents of warm air into shreds and wreaths, which curl and float and soar and at last lose themselves in the warmth that now wraps the earth.