After a discourse about the literature on visual acuity before Hume, I discuss how the "size" of visual objects is defined and determined. I shall then present circumstantial, but commanding, evidence for the influence of James Jurin's Essay upon Distinct and Indistinct Vision on Hume's thought. This work contains well-supported findings incompatible with claims made in T 1.2, "Of the ideas of space and time," and elsewhere. Specifically, the prominent principle of the Treatise, "[w]hat consists of parts is distinguishable into (...) them, and what is distinguishable is separable" (T 1.2.1.3; SBN 27) is shown to be false. A powerful principle, it is a premise to the most important arguments of the Treatise, but is shunned in the Enquiry and later writings because, I believe, Hume had read Jurin. (shrink)