146 Rutherford: Modern 



sidered that the rays were not corpuscular but consisted 

 of a special type of wave motion in the ether. 



A great advance was made in 1894 by Lenard when 

 he showed that the cathode rays were able to penetrate 

 matter opaque to ordinary light, and that the cathode 

 rays could be passed through a thin window and their 

 properties examined outside the vacuum tube. 



The discovery of the X-rays a little later directed sci- 

 entific attention to the great importance of elucidating 

 the true nature of the cathode rays. J. J. Thomson, in 

 1897, succeeded in completely demonstrating the general 

 correctness of the material hypothesis of Crookes. The 

 cathode rays did in truth consist of negatively charged 

 particles, which moved in the vacuum tube at the enor- 

 mous speed of about fifty thousand miles per second. 

 But a most remarkable fact was brought to light. The 

 mass of the particles of the cathode stream were extra- 

 ordinarily small, only about i/iooo of the mass of the 

 hydrogen atom. This was a great advance for it indi- 

 cated that the atom was not the smallest subdivision of 

 matter. These " corpuscles " or " electrons " thus be- 

 haved as the bodies of smallest mass known to science. 



J. J. Thomson soon showed that electrons of the same 

 small mass could be produced from different kinds of 

 matter in a variety of ways. Electrons, for example, are 

 freely emitted from the incandescent carbon filament of 

 an electric lamp ; they are emitted also from a metal 



