An accessible survey of X-rays, ultraviolet and related rays, their discovery and physical nature, and the wide range of practical and medical applications developed in the early 20th century. It describes radiographic techniques and instruments, therapeutic uses and reported curative claims, industrial and forensic applications such as flaw detection, metal analysis, art authentication and customs inspection, biological investigations including silk‑worm studies, and the health effects of sunlight and ultraviolet light. The text also recounts early accidents and injuries from radiation and offers historical anecdotes and illustrative cases to clarify methods and limitations.