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 geodesy, magnetism, optics.