1. Popular lectures on scientific subjects. Second series Author(s): Helmholtz, Hermann von, 1821-1894, author Publication: New York : D. Appleton and Co., 1881 Subject(s): Natural Science Disciplines
2. Popular lectures on scientific subjects Author(s): Helmholtz, Hermann von, 1821-1894 Publication: New York : Appleton, 1888 Subject(s): Natural Science Disciplines
