A cathode ray is a stream of electrons that are seen in vacuum tubes. It is called a "cathode ray" because the electrons are being emitted from the negative charged element in the vacuum tube called the cathode. A cathode ray tube aims the ray at a point on its screen. They were first observed in 1869 by German physicist Johann Hittorf, and were named in 1876 by Eugen Goldstein Kathodenstrahlen, or cathode rays.