This volume contains eleven articles, seven of them written by Leonhard Euler himself (4 contributions in Latin, 3 in French) and four written by his son Johann Albrecht Euler (3 contributions inFrench,1 in Latin). Four of the papers are prized essays submitted to the Académie Royale des Sciences in Paris and to the Imperial Academy in St. Petersburg. There are three articles on heat, two on matters of electricity and six articles on magnetism. The extensive introduction, written in English, is divided into the parts thermodynamics, electricity, magnetism, and several comments and appendices on Euler's "Anleitung zur Naturlehre", on Euler's summery of Aepinius' paper on electricity, and Euler's work in spherical trigonometry.