CROOKES TUBE. A sealed vessel of glass from which the air has been exhausted and a high vacuum through which a current from an induction coil or other source of high potential electricity is passed. A Crooke.: tube differs from it Geissler tube (q.v.) in the higher degree of its exhaustion and in several impor tant particulars which will appear in the de• seription of its operation given below. The name is derived from Sir, William Crookes (q.v.), who was able by his improvements in the Spren gel pump (see Aia-PumP) to obtain vacuum tubes of greater efficiency than those of previous investigators. Crookes was not the inventor of the highly exhausted tube, as Hitto•f, of Min ster (1869), had performed a number of experi ments with tubes having a comparatively high vacuum, but it remained for the English in vestigator to push the experiments still further and to formulate hypotheses and theories.
A Crookes tube contains two or more elec trodes known as the cathodes and anodes. These are formed by platinum wires which pass through the glass walls of the tube and terminate in metallic plates of the material and shape de sired for the experiment. The exhaustion is effected by connecting the tube to a mercurial air pump and then sealing it when the proper point is reached. The terminals are then connected with an induction coil which is set in operation. The important peculiarity of such a vacumn tube noticed by Professor Hitto•f consists of a fluorescence (q.v.) or golden-green glow pro duced on the glass opposite the cathode. There is not the brilliancy of glow that is found throughout the tube as in the Geissler tube. and •
the rays which produce the fluorescence issue from the surface of the cathode in straight lines normal or perpendicular to that surface, not being bent to follow the shape of the 011ie. as would be seen in tubes of a less degree of ex haustion. These cathode rays have many other interesting properties. They may be deflected by a magnet, and they cause a number of sub stances, such as diamonds and rubies, on which they impinge, to become brilliantly phosphores cent; their energy is sufficient to heat to a high temperature a surface on which they fail and can also he exhibited in causing a small wheel with mica vanes, mounted within the tube, to revolve as a result of the impact. Crookes used cathodes of plane, convex, and concave sur face. from which the rays would In. emitted in beams either parallel. diverging. or converging. After studying these rays and their properties he concluded that the discharge from the cathode represented a new form of matter which he Con sidered as existing in an ultra-gaseous or radiant state. The most important use of the Crookes tube is for the production of Illintgen rays. or X-rays (q.v.), which are the rays passing out from the tube opposite the cathode. To produce these rays a tube must he employed where the vacuum is adapted to the work in band, and there are self-regulating tubes on the market in which this properly is obtained. Set' ELECTRI