WILHELM HITTORF AND WILLIAM CROOKES 347 



a post as a chemist, which allowed him to found a 

 family. His important work was done in his own labora- 

 tory, which was much less cramped than Hittorf's uni- 

 versity laboratory. Crookes reached the high age of eighty- 

 seven. 



From the work of Hittorf and Crookes, large sections of 

 the physics of the ether have subsequently been developed. 

 It was only necessary to carry out exact experiments with 

 Hittorf's glow discharge, and Crookes' 'radiant matter' or 

 cathode rays, in such a way that they could be observed 

 under more various conditions than had hitherto been the 

 case in the discharge tube. This happened fifteen years 

 after Crookes' publication (1894). From that point all the 

 further progress followed quickly, which can only here be 

 indicated in outline: the discovery of high frequency rays 

 (X-rays), of radio-activity and radium, as well as of the other 

 radio-active elements of high atomic weight and their radia- 

 tions; the assured explanation of the nature of cathode rays, 

 and then also of the rays of the radio-active elements, and of 

 allied radiation such as the canal rays; the conduction of 

 electricity in gases and finally, in particular, the phenomena 

 of discharge at low pressures - which had been the starting 

 point of the whole matter - became fully understood. The 

 cathode rays themselves turned out to be free negative ele- 

 mentary electric charges separated from atoms - they were 

 called 'electrons' -just as Wilhelm Weber had imagined 

 them, without however, having been able to say anything 

 concerning their actual existence, and still less concerning 

 the possibility of completely separating them from matter. 



Also, the rays of Hittorf and Crookes brought quite fresh 

 information concerning the atoms of matter themselves. 

 This agreed in essentials with that already furnished by 

 Clausius from the kinetic theory of gases, but went beyond it; 

 the interior of the atoms now became accessible to investiga- 

 tion, in spite of their smallness, which removes them from 



