Dialling. Or The Art Of Drawing Dials (1770)

Emerson (1701-82) was a schoolteacher and mathematician. He became well known for his “comprehensive grasp of all existing knowledge in all branches of his subject”. He published a defense of Newton’s Principia and authored a textbook on fluxions (calculus). Even 80 years after his death, “the works of this able mathematician…[were] still in high estimation”. “[T]he first section contains the grounds of this art; by shewing how the several requisites are to be found… from the principles of spherical trigonometry. The second section contains the practice, and that three different ways. 1. Geometrically, by rule and compass, which depends upon the gnomonic projection of the sphere… 2. By trigonometrical calculation… which is the most exact way. 3. By the lines upon Collin’s Dialling scale, which is a method extremely easy and ready. The third section shews the way of making some other sorts of dials; and drawing the furniture upon any common diall.”