Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which by definition have the same molecular formula and sequence of bonded atoms (constitution), but differ in the geometric positioning of the atoms in space. For this reason, it is also known as 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question (dynamic stereochemistry). It was not until after the observations of certain molecular phenomena that stereochemical principles were developed. In 1815, Jean-Baptiste Biot's observation of optical activity marked the beginning of organic stereochemistry history. He observed that organic molecules were able to rotate the plane of polarized light in a solution or in the gaseous phase. Despite Biot's discoveries, Louis Pasteur is commonly described as the first stereochemist, having observed in 1842 that salts of tartaric acid collected from wine production vessels could rotate the plane of polarized light, but that salts from other sources did not. This property, the only physical property in which the two types of tartrate salts differed, is due to optical isomerism. In 1874, Jacobus Henricus van 't Hoff and Joseph Le Bel explained optical activity in terms of the tetrahedral arrangement of the atoms bound to carbon. Kekulé used tetrahedral models earlier in 1862 but never published these; Emanuele Paternò probably knew of these but was the first to draw and discuss three dimensional structures, such as of 1,2-dibromoethane in the Giornale di Scienze Naturali ed Economiche in 1869.