In early nineteenth-century London audiences flocked to a variety of lectures and shows on astronomical topics. While the religious and social positions of the lecturers and showmen varied significantly, the vast majority adopted a Newtonian cosmology incorporating a belief in the plurality of worlds. This paper focuses on Isaac Frost's 1846 book Two Systems of Astronomy in an attempt to gain a fuller understanding of how some thinkers in plebeian London responded to and resisted this emergent astronomical orthodoxy. Central to this analysis is research that reveals how changes in the intellectual world of Frost and his Muggletonian co-religionists prompted this formerly non-proselytizing Protestant sect to become increasingly vocal during the nineteenth century. This research is based upon a thorough examination of the Muggletonian archive in the British Library together with a collection of approximately thirty Muggletonian letters deposited in the Oxfordshire Records Office in 1993 and not examined by previous historians. It is concluded that the unorthodox or anti-Newtonian cosmologies advanced by several early nineteenth-century thinkers were often intellectually coherent and embodied in receptive social contexts.