Unique in American intellectual history, Charles Sanders Peirce (1839-1914) made important contributions to symbolic logic, of which he was one of the founders, and to the logic of science, as well as to mathematics, psychology, philosophy, astronomy, and other scientific fields. Volume 6 of this landmark edition contains 66 writings mainly from the unsettled period in Peirce's life just after he moved from New York to Milford, Pennsylvania, followed shortly afterward by the death of his mother. It begins with interesting remnants of Peirce's correspondence course in logic, by which he hoped in vain to make a living. Other notable selections include the much heralded "A Guess at the Riddle", Peirce's never-finished yet substantial attempt to draw his wide-ranging philosophical theories into a unified system of thought; his dispute with Edmund Gurney over Gurney's Phantasms of the Living; his attack, under the pseudonym 'Outsider', on Spencer's mechanical philosophy; and, lengthy excerpts from the report on gravity that led to his forced resignation from the U.S. Coast and Geodetic Survey. These and other writings in this volume reveal Peirce's powerful mind probing into diverse issues, looking for an underlying unity but, perhaps, also looking for direction.