2. Bruxelles, Hayez, Imprimeur de l'Académie, 1903, in-8°, 668 pp, sewn, original printed wrapper (back wrapper is missing, last leaf with some damage but no loss of text.). Published as a ''Mémoire Couronné de l'Académie Royale des Sciences...de Belgique''. Translation in French of a scientific treatise in German by Prof. Curt Weigelt on water treatment and improvement of the water quality in rivers. The study contains a large numbers of test on the influence of water polluting chemicals on fresh water fishes , mainly trout. Very early study on ecology, environmental protection.