686. Why do chimneys that stand under elevated objects, such as hills, trees, and high buildings, smoke?
Because the wind, striking against the elevated object, flies back, and a part of it rushes downward.
687. Why do sooty chimneys smoke?
Because the accumulation of the soot diminishes the size of the flue, and lessens the ascensive power of the draught, by reducing the quantity of warm air. It also obstructs the motion of the air, by the roughness of its surface.
688. Why do chimneys smoke in damp and gusty weather?
Because the ascending air is suddenly chilled by gusts of damp and cold air, and driven down the chimney.
"Remember that thou magnify his work, which men behold. Every man may see it; man may behold it afar off."—Job xxxvi.