from Faraday to J . J. Thomson. 393 



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 Plucker'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,f who found that distinct shadows were cast, not 

 only when the 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 VarleyJ put forward 

 the hypothesis that the rays are composed of " attenuated par- 

 ticles 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 



* Ann. <1. Phys. cxxxvi (1869), pp. 1, 197; translated, Annales de Cbimie, xvi 

 (1869), p. 487. 



t Berlin Monatsberichte, 1876, p. 279. 



J Proc. Roy. Soc. xix (1871), p. 236. 



Priestley in 1766 had shown that a current of electri6ed air flows from the 

 points of hodies which are electrified either vitreously or resinously : cf. Priestley's 

 History of Electricity, p. 591. 



