The paper that I presented at the Humours, Mixtures, and Corpuscles conference focuses on an English natural philosopher, Kenelm Digby, and his atomic interpretation of Aristotle. It demonstrates that Digby’s idiosyncratic engagement with the chymical and Aristotelian traditions led him to develop the innovative concept of effluvia that underpinned his influential “powder of sympathy”.   In the seventeenth-century medical tradition out of which Digby’s thought evolved, most learned physicians held that it was more efficacious to compound simples than to use them as stand-alone cures. With their skills, erudition, and experience, physicians were to select the best medical insights from the storehouse