This volume is primarily a textbook for students intending to specialize in radiology, radiotherapy or physical therapy. Sixteen chapters and an appendix deal with the production of alternating and direct currents, measurement, roentgen ray tubes, roentgen rays, electromagnetic waves, radioactivity, dosage and artificial radioactivity. Several pages of problems assist the student who wishes to refresh himself on the subject of physical phenomena. The author has tried to use as simple mathematics as possible. The specialist, either student or practitioner, in roentgen rays or physical therapy should find this book useful in his library.