Sir William Crookes was an English chemist and physicist who is best known for his pioneering work in the fields of vacuum and radiometry, as well as the invention of the Crookes tube, the first practical device for detecting and measuring cathode rays. In 1879, he conducted an experiment known as the Crookes’ tube experiment, which involved the use of an evacuated tube with two metal electrodes. When electric current was passed through the tube, a glowing beam of light was observed, and Crookes theorized that this was caused by invisible particles he called cathode rays. This experiment helped to establish the existence of electrons and provided the foundation for modern atomic theory.
