Original paper read to the Royal Society on 24 June 1802, reproduced as a twelve-page PDF hosted by MIT. Pages 365–366 describe determining refractive power from the boundary of total reflection, contact between specimen and prism, and a square-prism instrument with hinged sighting arms and a vernier. Page 366 compares genuine and suspected adulterated clove oil. The Royal Society manuscript catalog independently identifies the author and 1802 paper. Historical terminology is retained in the publication title.