Through other experiments he discovered that rays created images on photographic plates. These rays were know as Roentgen Rays but we know them as X-rays. They are part of the electromagnetic spectrum Other scientist such as: J. Plucker, J. W. Hittorf, C. F. Varley, E. Goldstein, Sir William Crookes, H. Hertz, and Ph. von Lenard, had already worked on this field. The work of these scientists the properties of cathode rays had become greatly known.