Meyer, Julius Lothar (1830-1895) was a German chemist who showed the relation between the atomic weights and properties of the elements. He developed a periodic table, which groups the chemical elements by their atomic weights and properties.

Meyer was born in Varel, Oldenburg, Germany. He studied medicine at the University of Zurich, and earned his M.D. degree at the University of Wurzburg in 1854. He then went to the University of Heidelberg, where he studied physiological chemistry under Robert Wilhelm Bunsen.

While working on his doctoral dissertation, Meyer researched the physiological aspects of the uptake of gases by the blood. He demonstrated that oxygen absorption by blood in the lungs occurred independently of pressure. He thought this was due to a loose chemical linkage. When he investigated carbon monoxide poisoning, he discovered a similar chemical linkage between that gas and a component of the blood. He also found that the amounts of oxygen and carbon monoxide taken up by the blood were in a molecular ratio, the oxygen being replaced volume for volume by the carbon monoxide. He concluded that the same blood component must therefore react with both gases. For this work, he earned his Ph.D. degree from the University of Breslau.

In 1859, Meyer became a privatdozent, or private lecturer, in physics and chemistry at Breslau. That same year, he became director of the chemical laboratory of the university's physiology department, lecturing on organic, inorganic, physiological, and biological chemistry.

He attended the 1860 Karlsruhe Congress, where he was greatly influenced by the presentation of Stanislao Cannizzaro's concept of establishing atomic weights and formulas. After the congress, he began research for Modern Theories of Chemistry (1864), in which he concluded that the properties of elements depended on their atomic weight. It was recognized as the best presentation of the fundamental principles of chemistry until the physiochemical movement began.

In 1866, Meyer worked at the School of Forestry at Neustadt-Eberswalde. Two years later, he became professor of chemistry and director of the chemical laboratories at the Karlsruhe Polytechnic Institute. During the Franco-Prussian War (1870–1871), Meyer contributed his medical skills and helped organize an emergency hospital in the Polytechnic buildings. In 1876, he became a professor of chemistry at the University of Tubingen, where he remained until his death.

Meyer continued studying the regular differences between the atomic weights of related elements. In 1864, he developed his first periodic table. He continued to work on it, and by 1868, he had developed a periodic table that is similar to the one used today. He had not yet published his work when, in 1869, Russian scientist Dmitri Ivanovich Mendeleev, who also had attended the Karlsruhe Congress, published a paper describing his version of the periodic table of elements. In 1870, Meyer published “Die Natur der chemischen Elemente als Function ihrer Atomgewichte.” This paper presented a revised form of the periodic table he had developed. It is noteworthy for its graphic display of the periodicity of atomic volume plotted against atomic weight. Meyer's table was quite similar to Mendeleev's but contained several improvements. Mendeleev, like Meyer, also revised his table several times and published articles describing the revision in 1870 and 1871. Although the work done by Meyer and Mendeleev closely corresponded, Meyer's focus was more on the periodicity of the physical properties of the elements, whereas Mendeleev was more interested in the chemical consequences of the periodic law.

As Mendeleev had, Meyer left some blank spaces on his periodic table. Meyer, however, was not as firm as his counterpart in his conviction regarding the prediction of undiscovered elements. Meyer stated that some elements had atomic weights that were as yet unknown, and he presumed that they might, at least in part, fill in some of the blanks on the table. Other blanks would perhaps be filled by elements yet to be discovered. Also, through future discoveries, some elements might be moved from their places and be replaced by more suitable ones.

Meyer also designed or improved many pieces of laboratory apparatus, which were used by other chemists. In 1882, Meyer was awarded the Davy Medal of the Royal Society with Mendeleev. He became a foreign honorary member of the Chemical Society (London) in 1883, and a corresponding member of the Prussian and St. Petersburg Academies of Sciences in 1888 and 1891, respectively. In 1892, he was given a title of nobility by decree of the Württemberg crown.