During the eighteenth century, academies and societies developed forms of life and of judgment that were set off from the universal criticism associated with learned journals. Despite the prominence of the Philosophical Transactions in historical narratives of modern science, the memoir collections associated with academies were a distinct and more prestigious form of publishing by the late eighteenth century, and the Transactions itself was eventually reshaped on this model. When publishers began to have measured success producing commercial periodicals focused on natural philosophy near century’s end, they hewed to prior models of journals and magazines: they often provided a locus for correspondence networks, and they digested, reprinted and translated content from elsewhere. But if the rise of a literary market was a source of ambivalence for the broader Republic of Letters, it was even more problematic as a model of natural philosophical judgment. Even while writing for periodicals became a means of making a career, scientific journals also became venues for printing (or reprinting) original research memoirs. As a potential alternative institutional locus for communal scientific activity, the periodical press presented a challenge to elite academies’ claims as the principal audience of scientific claims.