Antebellum mesmerism posed a challenge to the prerogatives of self-mastering reason from within the scientific tradition itself. Though mesmerism is now most familiar as the sensational stage-practice and quack cure that drew criticism from Hawthorne and Henry James, its sympathizers considered it a theory of sensory error. Mesmerists claimed that the trance replicated the physiological effects of deception, allowing them to study swindling in laboratory conditions. Concluding that sensory error was ineradicable, they refuted Lockean pedagogy's claims to reform the errant senses. One could at best manage delusion, through the self-doubt that liberalism had enjoined only its marginalized types—credulous women, laborers, racial inferiors—to practice. Mesmerism transvalued these figures, praising their powers of self-suspicion and condemning the ridiculous confidence of reason. Tracing the American mesmeric tradition from the science's first appearance there as a falsehood, in 1784; through its limited practice in the 1790s; to its extensive popularity from the 1840s to the end of the century, I find in its performances an alternate sensory public capable of including among its knowing subjects hysterics, renegades, and castaways. Rather than thinking of American publics as being formed through agreement on the procedures of reason, then, my project proposes that we see them as forming around the procedures of sensation that mesmerism discloses. Through readings of The Coquette (1797), Edgar Huntly (1799), Moby-Dick (1851), The Blithedale Romance (1853), and other works of fiction, I argue that this tradition constitutes a resource for the novel in holding open the gates of the public sphere to a pluralistic range of knowledge-producers. Forming oxymoronic crosses between good liberals and strange, errant, but insightful mesmeric knowers, American fiction creates stereoscopic images of impossible subjects.