This popular-science book of the famous Swiss mathematician, physicist, and mechanic Leonhard Euler (1707-1783) has a number of merits, which make it unique during the history of this genre. These are the depth of the text, comprehensiveness, and scientific value. The book is written in 3 volumes. Euler has touched virtually all aspects of his contemporary physics. The second volume is about the relations of body and soul, other theological issues, an introduction to logical theory, the essence of human knowledge, theory of electricity.