This is a most interesting work on the roentgen ray aside from its medical application. The first part is devoted to the early developments in physics of the theories of light, energy and roentgen rays. The authors later discuss the advances made in chemistry in studying the atom, the electron and crystal structure by means of roentgen rays. The discussion on early equipment and tubes is so complete as to remove the necessity of any future writer on clinical roentgenology devoting half the book to this subject. The authors further explain the industrial applications of the roentgen rays. They also point out the possibilities of further advancement and applications, clinically and industrially. The book is recommended to all students, radiologists, manufacturers and engineers who are interested in the roentgen ray.