Consider Francis Bacon as an essayist.
Bacon wrote no systematic discussion of rhetoric or essay writing himself, but scattered throughout his own essays are comments on his own approach, which differed significantly from what is known as the Ciceronian style that emphasized style (the arrangement of words) to subject matter.
In his essay The Advancement of Learning (1605), Bacon said that essays should primarily "apply Reason to Imagination for the better moving of the Will," and in a later essay, Bacon noted that "Rhetoric is subservient to the imagination, as Logic is to the Understanding." In essence, Bacon argued that essays should be based on logic and reason, which should take precedence over style or rhetorical techniques.
Bacon wrote almost a hundred essays on such subjects as "Divisions of Learning," "The Great Renewing" (in which he advocated a plan for organizing all knowledge), and the "Interpretation of Nature" (a full discussion of his philosophical views). Most of his essays are characterized by three stylistic features, consistent his view of the importance of subject over style: 1) the subject matter conforms to the style; 2) the use of relatively simple, direct vocabulary; and 3) a tone of reasonableness rather than attack.
Bacon's essays, because they are direct and succinct, are often compared to the writings of Tacitus. For example, one of Bacon's typical statements in an essay is "He who hath wives and children hath given hostages to Fortune," easily the subject of an entire essay by itself.