In 1845, 1846, and 1847 he wrote abundantly, widening his relations with the magazines of the day and apparently finding no trouble in marketing his wares. One piece of verse is preëminent in this period for both immediate and lasting appeal—“The Present Crisis.” It was Lowell’s way of protesting at the national policy in the war with Mexico and, in its contrast with Thoreau’s method (see p. 224), throws light on the reformer’s later strictures upon the recluse. It was repeated on every hand during the next twenty years and was given special emphasis through its frequent use by such orators as Wendell Phillips and Charles Sumner. It was in 1848, however, that he came to the fullness of his powers, contributing some forty articles to four Boston periodicals and publishing four books “Poems (Second Series),” “A Fable for Critics,” “The Biglow Papers,” and “The Vision of Sir Launfal.” He was only ten years out of college, and at that was only twenty-nine years old, but he showed secure taste, confident judgment, and a seasoned ease of humor which belong to middle life. In the first and last, the more literary volumes, there is perhaps more evidence of youth. It appears in the effusive grief on the loss of his little daughter, and in “Sir Launfal” Lowell seems to be working too clearly after the somewhat confused formula laid down in the introduction to The Pioneer. Americans were to attempt a natural rather than a national literature. They were to remember that “new occasions teach new duties.” “To be the exponent of a young spirit which shall aim at power through gentleness ... and in which freedom shall be attempered to love by a reverence for all beauty wherever it may exist, is our humble hope.” So in order not to be too aggressively national, he derived a theme from the literature of chivalry and adorned it with a democratic, nineteenth-century moral.

“A Fable for Critics” is less consciously ambitious and more mature. Just how remarkable a piece of discrimination it was can be seen from a comparison of the writers criticized in it with those in Poe’s “Literati” of two years earlier. Lowell’s subjects are familiar to the modern general reader; he omitted no man of permanent reputation and included almost no one who has been forgotten. Poe’s selections, on the other hand, are quaintly unfamiliar as a whole to all but the professed student of literary history. His judgments on them are mostly sound, but his judgment in choosing them for treatment is open to one of two criticisms: either that he could not recognize permanent values or that, for personal and editorial reasons, he preferred to ignore them. In the “Fable” Lowell for the first time put to public use his ready command of impromptu verse. His pen was a little erratic, but when it would work at all, it was likely to work with happy fluency. The jaunty treatment of his contemporaries was quite literally a series of running comments, trotting along in genial anapæstic gait, stumbling sometimes on a pun, scampering with light foot across extended metaphors, and taking the barriers of double and triple rime without a sign of exertion. In point of method the “Fable” was a single exercise in writing the journalistic verse of which Lowell proved himself master in the two series of “Biglow Papers” (1846–1848 and 1862–1866). It was exactly deserving of Holmes’s friendly comment, “I think it is capital—crammed full and rammed down hard—powder (lots of it)—shot—slugs—very little wadding, and that is guncotton—all crowded into a rusty-looking sort of a blunderbuss barrel, as it were—capped with a percussion preface—and cocked with a title-page as apropos as a wink to a joke.” Different as it is from “The Literati” in scale, tone, individual subjects, and method of circulation, the two deserve mention together as antidotes both to Anglomania and to wholesale praise of everything American.

With “The Biglow Papers” Lowell returned to the attack which he had begun in “The Present Crisis.” He wrote in 1860:

I believed our war with Mexico (though we had as just ground for it as a strong nation ever has against a weak one) to be essentially a war of false pretences, and that it would result in widening the boundaries and so prolonging the life of slavery.... Against these and many other things I thought all honest men should protest. I was born and bred in the country, and the dialect was homely to me. I tried my first “Biglow Paper” and found that it had a great run. So I wrote the others from time to time in the year which followed, always very rapidly, and sometimes (as with “What Mr. Robinson Thinks”) at one sitting.

He wrote the nine numbers of the series not only in the dialect of the countryside but from the viewpoint of a forthright, hard-headed, Puritan-tinged Yankee; and he put them out as the compositions of Hosea Biglow under the encouragement of Parson Wilbur, without the use of his own name. He was surprised by the cordial reception of the volume, fifteen hundred copies of which were sold in the first week. If he had put on the cap and bells to play fool to the public, he said, it was less to make the people laugh than to win a hearing for certain serious things which he had deeply at heart. “The Biglow Papers” were undoubtedly Lowell’s great popular success. They carried the fight into the enemies’ camp in the abolition struggle, they were resumed with new success with the outbreak of the Civil War, and they widened the reading public for his more sober political prose and for his more elevated verse.

However, Lowell was not satisfied to be only a fighter. In a letter of January, 1850, he wrote to a friend:

My poems hitherto have been a true record of my life, and I mean that they shall continue to be.... I begin to feel that I must enter on a new year of my apprenticeship. My poems thus far have had a regular and natural sequence. First, Love and the mere happiness of existence beginning to be conscious of itself, then Freedom—both being the sides which Beauty presented to me—and now I am going to try more wholly after Beauty herself.... I have preached sermons enow, and now I am going to come down out of the pulpit and go about among my parish.... I find that Reform cannot take up the whole of me, and I am quite sure that eyes were given us to look about us with sometimes, and not to be always looking forward.... I am tired of controversy.

Out of such a mood as this came the natural decision to make his first and long-deferred trip to Europe, a sojourn of fifteen months in 1851–1852 with his wife and children. His wide reading of foreign literatures gave the keys to an understanding of the peoples among whom he traveled, and especially to an understanding of Roman culture. His comments from Rome furnish an interesting contrast with Emerson’s (“Written at Rome,” 1833). The reaction of the Concord philosopher had been wholly personal. Lowell’s was wholly national.

Surely the American (and I feel myself more intensely American every day) is last of all at home among ruins—but he is at home in Rome.... Our art, our literature, are, as theirs, in some sort exotics; but our genius for politics, for law, and, above all, for colonization, our instinct for aggrandizement and for trade, are all Roman. I believe we are laying the basis of a more enduring power and prosperity, and that we shall not pass away until we have stamped ourselves upon the whole western hemisphere.

On his return to America he plunged eagerly into writing, but the springs of utterance were soon sealed by the death of his wife. Following on the losses of his mother and two of his children this was the fourth and most crushing bereavement within a very few years. His recovery of working powers was aided by the distraction that came from an invitation to deliver the distinguished Lowell Lecture Series in Boston in the winter of 1854–1855. These were to be twelve in number, on poetry in general and English poetry in particular. The task appealed to him as combining the beauty and truth to which he inclined to turn after his years of conflict. He threw himself whole-heartedly into the preparation and delivery of the lectures and succeeded admirably with his hearers; but the greater result was an indirect one. While they were in progress Longfellow offered his resignation of the Smith Professorship “of the French and Spanish Languages and Literatures ... and of Belles Lettres in Harvard College,” a post he had filled since 1836. Seven candidates of no mean ability presented themselves for the vacant position, but the appointment was offered to Lowell, who had not applied for it, in preference to them all. He spent another year abroad before undertaking the work in the autumn of 1856, and held the position actively until 1877 and as emeritus professor until his death in 1891. In this work he was a scholar and a critic rather than a teacher. He gave almost no elementary instruction in the languages, and his methods with his classes were casual to the neglect of the usual college traditions. What he did for his students was to share with them his own broad experience of life and letters and to show them how the study of foreign literatures was one with the study of history and philosophy.