The tenth Muse who now governs the periodical press.

Trollope’s phrase treats “the periodical press” as a modern cultural power comparable to the classical Muses—so powerful, in fact, that it deserves to be called a “tenth Muse.” The wording is ironical: instead of inspiring poetry or the arts, this new “Muse” governs public taste, reputation, and literary success through reviews, magazines, and newspapers. The line captures a Victorian anxiety about journalism’s growing authority over literature and public opinion, suggesting that writers and readers alike are increasingly subject to the rhythms and judgments of periodical culture rather than older, slower forms of literary consecration.