SCIENCE - BABINET Jacques (1794 - 1872) - Autograph letter signed Autograph letter signed, dated “Lundi 1er Février 1847” by the French physicist, mathematician, and astronomer who is best known for his contributions to optics. Among Babinet's accomplishments are the 1827 standardization of the Ångström unit for measuring light using the red Cadmium line's wavelength, and the principle (Babinet's principle) that similar diffraction patterns are produced by two complementary screens. He was the first to suggest using wavelengths of light to standardize measurements. His idea was first used between 1960 and 1983, when a meter was defined as a wavelength of light from krypton gas. Addressed to Pierre Rayer (1793 - 1867), Dean of the Faculty of Medicine: “…je regrette beaucoup qu’un mal de gorge obstiné dont il faut enfin que je me débarasse et que la longue et triste cérémonie d’hier a encore aggravé me prive du plaisir que j’attendais pour aujourd’hui de faire plus intime connaissance avec vous…”. 1 p. In-8. - This item is under temporary import. If the item is delivered within the United Kingdom, it will be subject to a 5% Value Added Tax (VAT) on the hammer price.