The Crookes tube is a vacuum-sealed glass container capable of carrying electricity. The original design included positive and negative electrodes and an induction coil to carry current.
When Crookes shot 10,000 volts of electricity through the tube, he witnessed a stunning and unexpected result: The tube glowed fluorescent green. Intrigued, he analyzed the mysterious energy flow and eventually deduced that the energy (composed of the yet-to-be discovered electrons) usually traveled in straight lines and applied pressure on anything in its path.
Other scientists quickly began studying and expanding upon Crookes' findings and inventions. As a result, in 1895, the first X-ray of human bones was made.