By the mid-19th century, scholars were beginning to analyse the history of institutional change, particularly the development of constitutional government. William Stubbs's "Constitutional History of England" (3 vols., 1874–1878) was an important influence on this developing field. The work traced the development of the English constitution from the Teutonic invasions of Britain until 1485, and marked a distinct step in the advance of English historical learning. He argued that the theory of the unity and continuity of history should not remove distinctions between ancient and modern history. He believed that, though work on ancient history is a useful preparation for the study of modern history, either may advantageously be studied apart. He was a good palaeographer, and excelled in textual criticism, in examination of authorship, and other such matters, while his vast erudition and retentive memory made him second to none in interpretation and exposition.