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.