From the publisher . The third volume of the physics course, widely known in our country and abroad The book is written on the basis of lectures, which for a number of years were read by the author to students of the Moscow Institute of Physics and Technology .. The main attention is paid to clarifying the physical meaning and content of the basic laws and concepts of electricity science, establishing the boundaries of the applicability of these laws, developing students' skills in physical thinking and the ability to set and solve specific tasks. For students of physical and mathematical faculties of universities, physico-technical and engineering-physical institutes, as well as universities where physics is the main discipline --------------The study of electricity includes three groups of questions. The first group includes the basic concepts and general principles that control electrical and magnetic phenomena; the second - electrical and magnetic properties of matter; the third - technical and practical applications of electricity. This course focuses on the issues of the first group, which are presented with the greatest completeness. Accepted inductive method. Basic concepts and principles are established by generalization of experimental facts having a limited scope of applicability .. The process of generalization is continuous and purposeful throughout the presentation, culminating in the middle of the course by establishing a system of Maxwell equations . All subsequent statements are constructed taking into account these equations. The electrical and magnetic properties of matter in the general course of physics cannot naturally be considered with the same degree of detail. Their full understanding is possible only on the basis of quantum mechanics, and detailed description should be made in special courses. Despite this, I have tried to pay much attention to this group of issues, as far as possible, within the framework of the general physics course intended for junior students .. At the same time, I widely used the methods ofthermodynamics .. Without the use of thermodynamics, it is impossible to fully and clearly describe not only the particular, but also the general issues of macroscopic electrodynamics. As for technical and other applications of the doctrine of electricity, these issues are given much less attention than they deserve. Of these issues, only a few are considered, and only from the principle side .. This is a continuation of the publication of the 1st and 2nd volumes .