Following Thomas Young’s ideas, light was regarded in the 19th century to move as vibrations (undulations) in a substance called the Luminiferous aether, contrary to Newton’s ideas that light itself was made of substantive corpuscles.
German researchers E. Wiedemann, Heinrich Hertz, and Eugen Goldstein believed they were 'aether vibrations', some new form of electromagnetic waves, and were separate from what carried the current through the tube.