William Jackson PopeFRS (31 October 1870 – 17 October 1939) was an Englishchemist. He studied crystallography under H. A. Miers and became deeply interested in it. In all his earlier researches much of his work was devoted to securing crystallographic data, and the hours he spent in the dark room with his goniometer were probably among the happiest in his life. These crystallographic studies had an important influence on the development of his chemical work, for they enhanced the natural faculty of visualising spatial relationships. This drew him inevitably into the field of stereochemistry where his greatest achievements were made. He obtained the chair of chemistry at Cambridge University in 1908.