The book "Conservation of Energy" by Stewart and Balfour is an important work in the field of physics. This book examines one of the basic laws of physics - the law of conservation of energy. The authors consider the history of the emergence of this principle, conduct a detailed analysis of its physical meaning and mathematical models corresponding to it. The book appeals to a wide range of readers who are interested in physics, science and the general laws of nature. Conservation of Energy introduces readers to important aspects of this key concept in physics, opening up the exciting world of science.