Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/413

 the tube, near the cathode, glowed with a phosphorescent light, and remarked that the position of this light was altered when the magnetic field was changed. This led to another discovery; for in 1869 Plücker's pupil, W. Hittorf, having placed a solid body between a point-cathode and the phosphorescent light, was surprised to find that a shadow was cast. He rightly inferred from this that the negative glow is formed of rays which proceed from the cathode in straight lines, and which cause the phosphorescence when they strike the walls of the tube.

Hittorf's observation was amplified in 1876 by Eugen Goldstein, who found that distinct shadows were cast, not only when he cathode was a single point, but also when it: formed an extended surface, provided the shadow-throwing object was placed close to it. This clearly showed that the cathode rays (a term now for the first time introduced) are not emitted indiscriminately in all directions, but that each portion of the cathode surface emits rays which are practically confined to a single direction; and Goldstein found this direction to be normal to the surface. In this respect his discovery established an important distinction between the manner in which cathode rays are emitted from an electrode and that in which light is emitted from an incandescent surface.

The question as to the nature of the cathode rays attracted much attention during the next two decades. In the year following Hittorf's investigation, Cromwell Varley put forward the hypothesis that the rays are composed of "attenuated particles of matter, projected from the negative pole by electricity"; and that it is in virtue of their negative charges that these particles are influenced by a magnetic field.

During some years following this, the properties of highly