This essay examines an outpouring of printed poems and biographical publications in the 1780s and 1790s that sought to shape the public image of the celebrated prison reformer John Howard. These materials, we argue, reveal the ways in which reform, empiricism, and Christian charity reinforced each other in late eighteenth-century popular imagination, and how this conjunction provoked a new vision of Britain’s empire and a backlash against mixing the scientific and the miraculous. As we show, Howard used the language of temperature to turn empirical data into evidence for the necessity of prison reform. This same thermometric language underwrote panegyric poems that represented Howard as global emissary of British benevolence—the icon of a new kind of empire whose power was symbolized by nearly miraculous capacity to temper inhospitable climates. This body of exuberant poetry transmuted data-based reform and technological advances in ventilation into proselytical triumph, a conjunction that was met, after Howard’s dramatic, self-inflicted death, with charges of overheated religious enthusiasm. As a result, Howard’s medical acquaintance and collaborators posthumously defended the temperateness of Howard’s empirical methods while also labeling him an amateur data collector, the lowly helpmeet of the professional man of science. By tracing Howard’s appearance in printed poetry and periodical writing, this essay illuminates the uneasy yet potent imbrication of reform culture, colonialism, medicine, and discipline formation in the final decades of the eighteenth century.