Graduation tower and the Water weel
Water wheel at Bad Nauheim-Schwalheim, powered by the Wetter. The wheel run the pumps at the graduation towers in Bad Nauheim by moving a bar.
A graduation tower consists of a wooden wall-like frame which is stuffed with bundles of brushwood. It increases the concentration of a solution of mineral salts. The salty water runs down the tower, and — through the action of breeze and sun — partly evaporates; at the same time certain mineral content of the solution are left behind on the sticks of brushwood.