Later, in 1869, Johann Wilhelm Hittorf studied discharge tubes with energy rays extending from a negative electrode, the cathode.
These rays produced a fluorescence when they hit a tube's glass walls, and when interrupted by a solid object they cast a shadow.
In the 1870s, Goldstein undertook his own investigations of discharge tubes and named the light emissions studied by others Kathodenstrahlen, or cathode rays.
It was another of Helmholtz's students, Wilhelm Wien, who later conducted extensive studies of canal rays, and in time this work would become part of the basis for mass spectrometry.
An object, such as a small ball of glass or iron, placed in the path of cathode rays produces secondary emissions to the sides, flaring outwards in a manner reminiscent of a comet's tail.