In September 1835 Williamson was appointed curator of the Museum of the Manchester Natural History Society, and so began his long connection with the great northern town, lasting down to 1892. In those days the interest in the vigorous young science of geology was extraordinarily keen, and there was great activity, especially among the naturalists of the North, many of whom were working men. Williamson, about 1838, gave a course of lectures on geology at various northern towns, and thus raised funds for his removal to London, to continue his medical studies. It is interesting to find that Williamson, while at Manchester, helped to nurse John Dalton in his last illness. While curator at Manchester, Williamson saw the rise of Binney as a geologist. His remarks on the local study of botany at that time are interesting. "The botanical interests of the district were chiefly in the hands of the operative community. The hills between Lancashire and Yorkshire swarmed with botanical and floricultural societies, who met on Sundays, the only day when it was possible to do so[124]." Some of these men must have had an excellent education, as shown by the good English they wrote, as for example Richard Buxton, a poor working man, author of a standard _Botanical Guide_. The society to which Buxton belonged had, in 1849, existed for nearly a century. It may be doubted whether an equal enthusiasm for science still prevails in that or in any part of England. In September 1840 Williamson went to London to complete his medical training, and entered University College, making the acquaintance of Prof. Lindley, who had for so long known him only as a correspondent and collaborator. Soon afterwards he was offered the post of naturalist to the Niger expedition, which he refused, and, as it turned out fortunately, for the journey proved disastrous. Stanger, of _Stangeria_ fame, took his place. In 1842, having then returned to Manchester and started in practice, Williamson made his first attempt at microscopic work, having become interested in the Foraminifera of the Chalk. He also began to examine Confervae, Diatoms and Desmids, finding perhaps, as others have done, that the Fresh-water Algae give the best introduction to microscopic biology. The work on Foraminifera became one of the most important in Williamson's career. In 1845 he wrote his valuable paper on microscopic organisms in the mud of the Levant. His work in this field culminated in his monograph of Foraminifera, issued by the Ray Society in 1857.