Eighteenth-century efforts to understand and prevent epidemics focused on correlating environmental circumstances with the ebb, flow and mortality of diseases like yellow fever. Riley describes the origins of this approach and its methodological shortcomings. He stops his story before the oft told tale of the demolition of this approach in the nineteenth century. He also speculates on why it remained popular for so long given its limited contribution to understanding disease. As someone who works in an area permeated with bad theories [psychiatry:] I found this 'natural history' of a wrong headed but well intentioned effort to understand disease quite fascinating.