In 1851 Williamson was appointed Professor of Natural History, which included Zoology, Botany and Geology, at the new Owens College, Manchester. He tells us, "The botanical portion of my work was that for which I was least prepared"--"of the German language I was utterly ignorant[125]." The almost insuperable difficulties of a triple Professorship were at first met by spreading the complete course over two years, a sensible plan which was rendered impracticable by the more rigid requirements of examinations. It was not, however, till 1872 that a division of the duties of the chair took place; Williamson was then relieved of the geological teaching by the appointment of Prof. Boyd Dawkins; in 1880 the zoology was taken over by the late Prof. Milnes Marshall, Williamson thus retaining the very subject, botany, with which he had originally been the least familiar. [Illustration: Plate XXII Vascular system of stem of _Lepidodendron selaginoides_ in transverse section. _Drawn by Williamson_] In addition to his peculiarly arduous duties as Professor, Williamson was a great populariser of science. He was one of the first two members of the Owens' staff to start, in 1854, evening classes for working men. He gave numerous scientific lectures at the Royal Institution in London and elsewhere, his greatest work in this field being his lectures for the Gilchrist Trustees. He mentions that from 1874 to 1880 he delivered 158 of these lectures in 61 towns, and he continued this work with equal activity for another 10 years. He was a vigorous and effective lecturer, who always interested his audience; he illustrated his lectures by bold diagrams, drawn by his own hand. In order to form any idea of Williamson's many-sided activity it must be remembered that he was all the time engaged in active medical practice, both general and special, for he was well known as an aurist. Yet he always found time for fruitful original research, often of the most laborious character. Prof. Judd says, in a letter written to me in February 1911: "I have often been struck by the fact that Williamson, appointed to an impossible Professorship of Zoology, Botany and Geology, managed to initiate _great movements_ in connection with _each of these sciences_. "In Geology he was clearly the pioneer in the subdivision of formations into zones each characterised by an assemblage of fossils--Ammonites playing the most important part.... But Williamson did another great service to Geology.... Sorby visited Williamson at Manchester and learned the art of making sections which he applied with such success to the study of igneous and other rocks, becoming the 'Father of Micropetrography.'