This essay revisits Edmond Halley's schema of a multi-sphered, hollow earth, presented to the Royal Society in 1691 as a hypothetical resolution to the problem of magnetic variation. I open my investigation with a reading of Michael Dahl's final portrait of the great astronomer (1736), which enigmatically reproduced a diagram of the hollow earth that Halley had appended to his original “Account […] of the Internal Parts of the Earth” in the Philosophical Transactions. My essay has the goal of enhancing our appreciation not only of Halley's aptitudes as a theorist of the earth sciences, but as the dexterous practitioner of a language felicitously attuned to the early development of that field. I provide a comprehensive exposition of Halley's self-styled “Extravagant” hypothesis and argue that his attachment to it was sustained by his adherence to the tenet of a divinely ordained, natural economy. I also position Halley's “Account” as the originary moment of a literary sub-genre—the hollow earth fantasy or romance—that flourished in England and America in his wake. Today, Dahl's painting gestures simultaneously to Halley's conception of a habitable inner earth and to a literary tradition that embraced that idea as its central imaginary novelty.