In 1895, Wilhelm Roentgen accidentally discovered that a cathode-ray tube could make a sheet of paper coated with barium1895年，威廉·伦琴偶然发现阴极射线管能使涂有一层氰亚铂酸盐钡的薄相纸发光，甚至当阴极射线管和相纸分别放在不同的房间时也能发光。