Purely physical evidence, based upon its thermo-chemical and optical characters can be adduced in its support. Determinations of the molecular volume and magnetic rotation of its compounds further serve to substantiate it. [Illustration: AUGUST KEKULÉ VON STRADONITZ.] │Friedrich August Kekulé│ was born at Darmstadt on September 7, 1829. After passing through the gymnasium of his native town, he entered, in 1847, the University of Giessen, with the intention of becoming an architect. Attracted by Liebig’s teaching, he turned to chemistry, and worked with Will on _amyl sulphuric acid_ and its salts. In 1851 he went to Paris, heard Dumas’s lectures, and formed a friendship with Gerhardt, whose _Traité de Chimie Organique_ largely moulded his views. He became an assistant to Von Planta, occupying himself with the chemistry of the alkaloids. Subsequently he came to London, worked under Stenhouse, and made the acquaintance of Williamson, then in the full vigour of his scientific activity. Here he discovered _thioacetic acid_. It was at this time, also, that his ideas with regard to structural chemistry began to take shape. Returning to Germany, he attached himself to the University of Heidelberg as a _privat-docent_, and had for a pupil Baeyer, who took up the study of the organo-arsenic compounds. In 1858 he published his memorable paper “On the Constitution and Metamorphoses of Chemical Compounds and on the Chemical Nature of Carbon,” in which he developed his views on the linking of atoms, out of which has grown our system of constitutional formulæ. The immediate result of this celebrated memoir was a call to the chemical chair of the University of Ghent, where Kekulé had among other students Baeyer, Hübner, Körner, Ladenburg, Linnemann, and Dewar. Here he remained nine years, and here he published his classical _Lehrbuch der Organischen Chemie_. The years he spent in Ghent were the most productive time of his career, and it was there that he developed his benzene theory—a conception as fruitful as that of his doctrine of atom-linking. In 1867 Kekulé was called to Bonn to take charge of the newly erected laboratory which Hofmann had designed. Although he continued to work, mostly in collaboration with his pupils, among whom may be named Anschütz, Bernthsen, Thorpe, Carnelley, Claisen, Dittmar, Franchimont, Van ’t Hoff, Japp, Schultz, Wallach, and Zincke, his health after 1876 began to fail. He died on July 13, 1896. * * * * *