How does the matter of the lodestonelodestone differ from other substances? The understanding of magnetism had to wait until the atomic constitution of matter was established, and the laws that rule the atomic and subatomic world were known in the first decades of the twentieth century. The idea of atoms has a long history; one of the earliest proposers was DemocritusDemocritus (c. 460–c. 370 BC). In the eighteenth century, Antoine-Laurent Lavoisier (1743–1794) characterized the idea of an element. John DaltonDalton, John (1766–1844), from the proportions in weight of elements that entered a chemical reaction, established that atoms are the smallest units of matter. Dmitri MendeleevMendeleev, Dmitri (1834–1907) drew a chart with 63 chemical elements, the “periodic table.” Joseph John Thomson (1856–1940) identified negative particles, later known as electrons. Max Planck (1858–1947) proposed in 1900 the existence of the quantum. Albert Einstein (1879–1955) quantified the radiation. Ernest Rutherford (1871–1937) discovered in 1909 that the atom is mostly empty space. Niels Bohr (1885–1962)Bohr, Niels created in 1912 the first quantum description of the atom. LouisLouis XV de Brogliede Broglie, Louis (1892–1987) established that all matter has wave properties. Erwin Schrödinger (1887–1961) and Paul Dirac (1902–1984) formulated equations to describe quantum systems. Dirac characterizes the post-1925 years as Dirac, Paul Adrianthe Golden Age of PhysicsSchrödinger, Erwin.