These lectures were written rapidly, many of them during the period of delivery of the course; they bore marks of hastiness of composition, but they came from a full and rich mind, and they were the issues of familiar studies and long reflection. No such criticism, at once abundant in knowledge and in sympathetic insight, and distinguished by breadth of view, as well as by fluency, grace, and power of style, had been heard in America. They were listened to by large and enthusiastic audiences, and they did much to establish Lowell's position as the ablest of living critics of poetry, and, in many respects, as the foremost of American men of letters. In the same year he was made Professor of Belles-Lettres in Harvard University, and after spending somewhat more than a year in Europe, in special preparation, he entered in the autumn of 1856 upon the duties of the chair, which he continued to occupy till 1877, when he was appointed Minister of the United States to Spain. During the years of his professorship he delivered numerous courses of lectures to his classes. Few of them were written out, but they were given more or less extemporaneously from full notes. The subject of these courses was in general the "Study of Literature," treating in different years of different special topics, from the literature of Northern to that of Southern Europe, from the Kalevala and the Niebelungen Lied to the Provençal poets; from Wolfram von Eschenbach to Rousseau; from the cycle of romances of Charlemagne and his peers to Dante and Shakespeare. Some of these lectures, or parts of them, were afterward prepared for publication, with such changes as were required to give them proper literary form; and the readers of Lowell's prose works know what gifts of native power, what large and solid acquisitions of learning, what wide and delightful survey of the field of life and of letters, are to be found in his essays on Shakespeare, on Dante, on Dryden, and on many another poet or prose writer. The abundance of his resources as critic in the highest sense have never been surpassed, at least in English literature.