This chapter locates Emerson’s late-phase interest in aggregated, communal forms of intellection within similar fixations that permeated a broader cultural ambience during the 1850s and 1860s. This milieu included the oceanographer Matthew Fontaine Maury, whose crowdsourced researches captured public imagination as a model of communal thought; Herman Melville, whose mention of Maury in Moby-Dick (1856) portends his own vision of a proliferating and ever-closer association upon the waves; Walt Whitman, whose similar interests in communality inform the oceanic and liquid setting of “Sun-Down Poem” from the second edition of Leaves of Grass (1856); and indeed Emerson, whose 1862 “Perpetual Forces” foreran the even more fluid social subjectivity of Natural History of Intellect (1870–71). Finally, the chapter argues that Emerson’s ideas in these last two works provided a template for the radical pluralism of William James’s Principles of Psychology (1890) and “How Can Two Minds Know One Thing?” (1905).