This preface to the treatise on electricity and magnetism by E. Mascart and J. Joubert, translated by E. Atkinson, introduces the book's structure and aims. The book is divided into two parts: the first part is theoretical, focusing on general phenomena and theory, while the second part will be more experimental, examining various phenomena, measurement methods, and applications. The authors emphasize the importance of understanding the general principles of the science to facilitate the explanation of experiments. They highlight the contributions of Faraday and Clerk Maxwell to the understanding of lines of force and the role of the medium in electrical and magnetic actions. The book aims to simplify demonstrations without sacrificing rigor, making it accessible to physicists while maintaining a high level of scientific accuracy. The preface also acknowledges the influence of other physicists, particularly Sir W. Thomson and Clerk Maxwell, and notes corrections and new proofs included in the English edition. The content covers statical electricity, electrical currents, magnetism, and electromagnetism, with detailed chapters on potential, electrical fields, lines of force, and the equilibrium of conductors.This preface to the treatise on electricity and magnetism by E. Mascart and J. Joubert, translated by E. Atkinson, introduces the book's structure and aims. The book is divided into two parts: the first part is theoretical, focusing on general phenomena and theory, while the second part will be more experimental, examining various phenomena, measurement methods, and applications. The authors emphasize the importance of understanding the general principles of the science to facilitate the explanation of experiments. They highlight the contributions of Faraday and Clerk Maxwell to the understanding of lines of force and the role of the medium in electrical and magnetic actions. The book aims to simplify demonstrations without sacrificing rigor, making it accessible to physicists while maintaining a high level of scientific accuracy. The preface also acknowledges the influence of other physicists, particularly Sir W. Thomson and Clerk Maxwell, and notes corrections and new proofs included in the English edition. The content covers statical electricity, electrical currents, magnetism, and electromagnetism, with detailed chapters on potential, electrical fields, lines of force, and the equilibrium of conductors.