The Crookes tube is a type of vacuum tube invented by Sir William Crookes in the 1870s. It consists of a sealed glass container from which most of the air has been removed, allowing electrons to flow freely between two electrodes. When a high voltage is applied, a beam of particles, known as cathode rays, is produced. This device played a crucial role in the study of electricity and radiation. The experiments conducted with the Crookes tube led to the discovery of the electron and laid the groundwork for modern physics, influencing technologies such as television and X-rays.