The book in a popular form, but quite strictly describes the experiments that played a crucial role in the transition from classical ideas to the ideas of modern physics and formed the basis of quantum mechanics and atomic theory. An interesting presentation with a large number of quotes from the works of scientists who performed the described experiments introduces the reader to the complex ways in which scientific ideas often develop, and facilitates the perception of these ideas themselves. The book is designed for a wide range of readers interested in physics and the history of its development, in particular for students and schoolchildren.