This article concerns the use of rhetorical strategies in the natural historical and anatomical works of the seventeenth-century Royal Society. Choosing representative works, it argues that naturalists such as Nehemiah Grew, John Ray and the neuroanatomist Thomas Willis used the rhetorical device known as ‘comparison’ to make their descriptions of natural things vivid. By turning to contemporary works of neurology such as Willis's Cerebri Anatome and contemporary rhetorical works inspired by other such descriptions of the brain and nerves, it is argued that the effects of these strategies were taken to be wide-ranging. Contemporaries understood the effects of rhetoric in terms inflected by anatomical and medical discourse—the brain was physically altered by powerful sense impressions such as those of rhetoric. I suggest that the rhetoric of natural history could have been understood in the same way and that natural history and anatomy might therefore have been understood to cultivate the mind, improving its capacity for moral judgements as well as giving it knowledge of nature.

In February 1670/1 the naturalist Martin Lister wrote to his colleague John Ray about a set of queries concerning spiders that he had sent to be published in the Royal Society's Philosophical Transactions. There, he complained about the description in Aristotle's Historia Animalium of the manner in which spiders dart their threads. Lister found the description to be accurate, but not vivid enough to enable even an informed reader to form an adequate mental image: ‘Which Text, tho’ very plain in it self, yet it will not easily enter into our Imagination, before we have made the Observation by Sense; witness the Misinterpretation of Redi and Blancanus.' To circumvent the flatness of Aristotle's words, Lister (as he confessed to Ray) deliberately mistranslated them: ‘in the Sett of Enquiries I sent to Mr. Oldenburgh, I have purposely given, to incite the Curious, another Interpretation of the Text.’1 Lister hoped to encourage his readers to question the description that they encountered, and to attempt their own observations. This would equip them to see what Aristotle had accurately, but lifelessly, described. Lister and Ray understood, however, that the work of natural history could not be accomplished successfully by resorting to tricking readers into making their own observations every time it became hard to represent something. Instead, as I argue in this essay, they used strategies derived from rhetorical theory and anatomical descriptions of the brain and senses for impressing vivid images into the imaginations of their readers. I also want to suggest that by analysing the vivid style that they used we can come to better appreciate the purposes, both epistemological and moral, that they wanted natural history and anatomy to serve for their readers.