The perpetual calculator: or, time's universal standard. [electronic resource] : In three parts. I. A plain and easy Introduction to Chronology since its last Improvement, containing an historical Account of the Old and New Stile, with plausible Reasons for changing the same. Rules for finding the Age and Change of the Moon, and whatever depends thereon, for ever. II. An Account of the Solar System, explaining the Laws and Means whereby the Planets are preserved in their Orbits: The Cause of Eclipses, and how to calculate them perpetually: A Synopsis of Comets, shewing how to predict the Appearance of four remarkable ones: A Synopsis of Astronomy, with Rules for discovering the Motions of the Celestial Bodies, how to acquire their Magnitudes, periodical Revolutions, diurnal Motions, Distances, &c. Invention of the Zodiac: Rules for the Equation of Time, &c. III. Pneumatics and Hydrostatics, or the Science of Fluids displayed; containing the Doctrine of Tides, Generation of Meteors, and Changes of the Weather. To which is annexed, an Appendix, Containing, Several useful Articles relative to those important Sciences. By R. Wetherald, philomath.