The prose of Thoreau is daily winning recognition as possessing some of the very highest qualities of thought and utterance, in a degree scarcely rivalled in contemporary literature. In spite of whim and frequent over-refining, and the entire omission of many important aspects of human life, these wondrous merits exercise their charm, and we value everything which lets us into the workshop of so rare a mind. These letters, most of which were addressed to a single confidential friend, give us Thoreau's thoughts in undress, and there has been no previous book in which we came so near him. It is like engraving the studies of an artist,--studies many of which were found too daring or difficult for final execution, and which must be shown in their original shape or not at all. To any one who was more artist than thinker this exhibition would be doing wrong; but to one like Thoreau, more thinker than artist, it is an act of justice. The public, being always eager for the details of personal life, and therefore especially hungry for private letters, will hardly make this distinction. All is held to be right which gives us more personality in print. One can fancy the exasperation of a gossip, however, on opening these profound and philosophic leaves. There is almost no private history in them; and even of Thoreau's beloved science of Natural History, very little. He does, indeed, begin one letter with "Dear Mother, ... Pray have you the seventeen-year locust in Concord?" which recalls Mendelssohn's birthday letter to his mother, opening with two bars of music. But even such mundane matters as these occur rarely in the book, which is chiefly made up of pure thought, and that of the highest and often of the most subtile quality.