THE LATEST STAGE 235 



The passage of an electric discharge through rare- 

 fied gases had been studied by Crookes, J. J. Thomson 

 and others for many years, and the theory of electric 

 ions, framed, as we have seen, to explain the conduc- 

 tion of electricity through liquids, had been adapted 

 to this case also. But in 1895 W. Rontgen of Munich 

 discovered accidentally that photographic plates stand- 

 ing in the neighbourhood of an electric discharge tube 

 were affected though covered with an opaque screen, 

 and thus revealed the rays associated with his name. 



When an electric discharge is passed between two 

 wires in a gas which has been very highly rarefied, 

 Corpuscles straight rays are found to proceed from 

 and Electrons. j- ne negatively electrified wire or cathode, 

 and to produce Rontgen rays when they strike solid 

 objects. These straight cathode rays have been 

 studied closely, especially by Sir Joseph John Thom- 

 son and his pupils. Thomson has also more recently 

 examined the positive rays which, also in straight 

 paths, proceed from the positive wire or anode. By 

 making these rays pass through intense fields of 

 magnetic and electric force, they may be deflected 

 from their straight course, and, from the deflection 

 caused by known forces, their velocity and their mass 

 can be calculated. They are found to consist of flights 

 of isolated atoms, and the experiments give an accurate 

 means of measuring the atomic weight. 



By similar methods, the negative or cathode rays 

 had already been examined. They were shown to 

 consist of flights of more minute particles negatively 

 electrified, and, again by measuring the electric and 

 magnetic forces required to deflect the particles from 



