While the Professor still occupied the Hebrew Chair, he had shown a special aptitude for another branch of learning, in which he was yet to make a reputation for himself in the Churches not only of Britain but of America. In 1866 he published a lecture, primarily addressed to his students, on 'The Westminster Confession of Faith: A Contribution to the Study of its Historical Relations and to the Defence of its Teaching,' which, as a reply to views then current in certain quarters, attracted no little notice at the time of its publication, and which is not only of special interest as illustrating his theological standpoint, and the calm and temperate, yet earnest and vigorous, manner in which he could defend it, but is of permanent value as a contribution to the literature of the subject with which it deals. In the following year he published 'The Wedderburns and their Work, or the Sacred Poetry of the Scottish Reformation in its Relation to that of Germany'--a subject which was treated by him much more fully in one of his most recent works. The Professor was known to possess a most extensive and accurate knowledge of Church History in general, and of Scottish Church History in particular; and when in 1868 he was called to occupy the Chair of Ecclesiastical History in St Mary's College, the appointment was hailed with satisfaction alike by the University and the Church. With an absorbing interest in his subject, and with the true instinct of the historian, he was most painstaking in ascertaining historical facts, never reaching his conclusions but as the result of patient and careful investigation; and those who knew him intimately can tell how little he grudged the trouble of a journey to Edinburgh or London, or even of an occasional excursion to the Continent, in order to prosecute his researches in libraries there with the view of verifying a statement, or of obtaining indubitable evidence on some controverted point. Besides those who had the privilege of listening to his prelections from the professorial chair, there are many in the Churches on both sides of the Atlantic who have profited by his great erudition; and his published writings, which all bear the impress of a master-hand, will always be reckoned standard works in Ecclesiastical History.