The Crookes tube is an electrical discharge tube fitted with a partial or fractional vacuum, similar to the Geissler tube but more than just a display piece. William Crookes developed his namesake between 1869-1875 and was later knighter for his scientific achievements earning the moniker Sir.
Significant about the device is that it formed the basis of the discovery of cathode rays. The basic structure is a container made of glass of any preferred shape fitted with two electrodes, a positive anode (+) and negative (-) cathode. These terminals are placed at two opposite ends of the tube.
Application of a high electric voltage between the two terminals result in a stream of electrons or cathode rays. These rays are normally projected in straight lines coming from the negative electrode, hence the name cathode ray. The motion of cathode rays is harnessed in many of Crookes tubes to produce motion, various photolumenecent effects and even X-Rays.
Crookes’ tubes are considered cold cathode tubes as they lack heated filaments as an electron source such as in transistor tubes. Despite "cold" in cold cathode ray, plasma generated in such tubes can reach many thousands of degrees.
Many scientific greats of the day including Hertz experimented and made significant discoveries with this style of tube. The most notable discovery being cathode rays by Wilhelm Rontgen Ca. 1895.
The Theory Behind Sir. Crookes' Tubes