34 FORESHADOWING OF THE ELECTRON [CH. iv. 



flows through metals, an effect discovered by E. H. 

 Hall in America, and known as the Hall effect. 



The fact that the particles are thrown off the 

 cathode, being evidently vigorously repelled by it, is 

 sufficient to suggest that they must be negatively 

 charged ; the direction of the curvature caused by a 

 magnetic field enables us to verify at once that the 

 flying particles are negatively charged, and no 

 comparable rush of positive particles in the opposite 

 direction, or in any direction, has been observed. 

 The speed of transmission of the positive current is 

 very great, and it must be conveyed by a multitude 

 of positive particles, but individually their motion 

 is comparatively slow (see however chap. vi.). In 

 that respect evidently the magnetic curvature of 

 cathode rays in gases differs from the magnetic 

 curvature of a current in metals ; viz., that whereas 

 in metals the major action is sometimes upon the 

 negative and sometimes upon the positive stream, 

 according to the nature of the metal the difference, 

 which is all that is observable, being always small, 

 in the cathode stream it is the negative alone -that 

 is acted upon, and so the action is always large. 



It seems, therefore, that for some reason or other 

 the negatively charged bodies in a vacuum tube are 

 much more mobile than the positive, and that the 

 mobility of the negatively charged bodies is extreme. 

 One striking method by which their mobility was 

 displayed consisted in the fundamental observation 

 by Professor Schuster* that all parts of gas in a 

 closed vessel became conducting when an electric 

 discharge had taken place in one corner of it; so 

 that even though the vessel consisted of different 

 compartments, one compartment was made feebly 



* Bakerian lecture 1890, Proc. Roy. Soc., vol. 47, p. 526. 



