A collection of learned essays surveys skeptical and natural-philosophical topics, arguing through paradoxes and observation. Early discourses challenge received elemental doctrines by comparing concentrated solar effects with common fire, reassessing the natural qualities of air and water, and urging experiment over speculative proportion. Subsequent pieces critique the display of superficial erudition, explore moral and political contraries, and defend experience as the chief arbiter of knowledge. The final essays consider variation in intellectual faculties among peoples and reflect on how talent and custom shape judgment, combining practical examples with philosophical skepticism.