From what fact or event shall we really date the beginning of spring? The little piping frogs usually furnish a good starting point. One spring I heard the first note on the 6th of April; the next on the 27th of February; but in reality the latter season was only about two weeks earlier than the former.... The little piper will sometimes climb a bullrush to which he clings like a sailor to a mast, and send forth his shrill call. There is a Southern species, heard when you have reached the Potomac, whose note is far more harsh and crackling. To stand on the verge of a swamp vocal with these, pains and stuns the ear.

Then in a foot-note:

The Southern species is called the green hyla. I have since heard them in my neighborhood on the Hudson.

Never was there writer who kept his feet more firmly on solid earth. He takes nothing for granted; he is satisfied only with the testimony of the senses, and his own senses. Everything—example, allusion, figure of speech, subject and predicate—comes from him in the concrete. Everything is specific, localized, dated. He was in accord with his era that demanded only reality. It is the task of the writer, he declared, "to pierce through our callousness and indifference and give us fresh impressions of things as they really are."

How permanent is such work? How valuable is it? Is Nature then a thing simply to be observed and classified and reduced to formulæ? To determine the average day on which the bluebird comes, or the wild geese fly, or the hyla calls, is there virtue in that? To Burroughs, Nature was a thing to be observed accurately for new facts to add to the known. Of Thoreau he wrote: "Ten years of persistent spying and inspecting of Nature and no new thing found out." Do we ask of the poet and the seer simply for mere new material phenomena found out to add to our science? The supreme test that must come at last to all literature is the question: How much of human life is there in it? How much "Thus saith the Lord"? Who seeks for material things with eyes, however keen, and dreams of no sources of the Nile, no vision that may come perchance from supernatural power latent in bird and leaf and tendril, is a scientist, however charming he make his subject or however sympathetic be his attitude. Judged by such a standard, Burroughs falls short, far short of a place with the highest. He must decrease, while Thoreau increases. He must be placed at last among the scientists who have added facts and laws, while Thoreau is seated with the poets and the prophets.

But though he be thus without vision and without message, save as an invitation to come to material Nature and learn to observe is a message, Burroughs has a charm of manner and a picturesqueness of material that are to be found in few other writers of the period. His power lies in his simplicity and his sincerity. He is more familiar with his reader than Thoreau. He is never literary, never affected; he talks in the most natural way in the world; he tells story after story in the most artless way of homely little happenings that have passed under his own eye, and so charming is his talk that we surrender ourselves like children to listen as long as he will. When we read Thoreau we are always conscious of Thoreau. His epithets, his distinction of phrase, his sudden glimpses, his unexpected turns and climaxes, his humor, for in spite of Lowell's dictum, he is full of humor, keep us constantly in the presence of literature; but with Burroughs we are conscious of nothing save the birds and the season and the fields. We are walking with a delightful companion who knows everything and who points out new wonders at every step.

The poetry of Burroughs faded more and more from his work with every book, and the spirit of the scientist, of the trained observer impatient of everything not demonstrable by the senses, grew upon him, until at length it took full control and expressed itself as criticism, as scientific controversy, and as philosophical discussion. Riverby, 1894, with its prefatory note stating that the volume was "probably my last collection of out-of-door papers," marks the point of division between the two periods. If we follow the Riverside edition, at present [1914] the definitive canon, eight books preceded Riverby and eight followed it. The groups are not homogeneous; it is not to be gathered that on a certain date Burroughs abandoned one form of essay and devoted himself exclusively to another, but it is true that the work of his last period is prevailingly scientific and critical. His Indoor Studies, 1889, Whitman, a Study, and Literary Values are as distinctively works of literary criticism as Arnold's Essays in Criticism; his Light of Day discusses religion from the standpoint of the scientist; his Ways of Nature is scientific controversy; and his Time and Change and The Summit of the Years are philosophy.

It is in this second period that Burroughs has done his most distinctive work, though not perhaps his most spontaneous and delightful. By temperament and training he is a critic, a scientific critic, an analyzer and comparer. Only men of positive character, original forces, attract him: Emerson and Whitman, and later Wordsworth, Carlyle, and Arnold, men who molded the intellectual life of their age. His first published book had been a critical study, Notes on Walt Whitman, 1867, a work the most wonderful in many ways of his whole output. It came at a critical moment, in those pregnant closing years of the sixties, and it struck clear and full the note of the new period. Burroughs's later studies of Whitman are more finished and more mature than this never-republished volume, but they lack its clarion quality. It is more than a defense and an explanation of Whitman: it is a call to higher levels in literature and art, a call for a new definition of poetry, a condemnation of that softness and honey sweetness of song that had lured to weakness poets like Taylor and Stoddard. Poetry henceforth must be more than mere beauty for beauty's sake: it must have a message; it must come burning from a man's soul; it must thrill with human life.

And it is here that Burroughs stands as a dominating figure. He was the first of American critics to insist without compromise that poetry is poetry only when it is the voice of life—genuine, spontaneous, inevitable. "How rare," he complained in later years, "are real poems—poems that spring from real feeling, a real throb of emotion, and not from a mere surface itching for expression." This has been the key to all his criticism: literature is life, the voicing of a man's soul. Moreover, it is a voicing of the national life, the expression of a nation's soul:

All the great imaginative writers of our century have felt, more or less, the stir and fever of the century, and have been its priests and prophets. The lesser poets have not felt these things. Had Poe been greater or broader he would have felt them, so would Longfellow. Neither went deep enough to touch the formative currents of our social or religious or national life. In the past the great artist has always been at ease in Zion; in our own day only the lesser artists are at ease, unless we except Whitman, a man of unshaken faith, who is absolutely optimistic, and whose joy and serenity come from the breadth of his vision and the depth and universality of his sympathies.[83]