Throughout his career the geographer, and first reader in the ‘new’ geography at the University of Oxford, Halford Mackinder (1861–1947) described his discipline as a branch of physics. This essay explores this feature of Mackinder's thought and presents the connections between him and the Royal Institution professor of natural philosophy John Tyndall (1820–1893). My reframing of Mackinder's geography demonstrates that the academic professionalization of geography owed as much to the methods and instruments of popular natural philosophy and physics as it did to theories of Darwinian natural selection. In tracing the parallels between Tyndall and Mackinder, and their shared emphasis upon the technology of the magic lantern and the imagination as tools of scientific investigation and education, the article elucidates their common pedagogical practices. Mackinder's disciplinary vision was expressed in practices of visualization, and in metaphors inspired by physics, to audiences of geographers and geography teachers in the early twentieth century. Together, these features of Mackinder's geography demonstrate his role as a popularizer of science and extend the temporal and spatial resonance of Tyndall's natural philosophy.