46 THE FOUNDATIONS OF SCIENCE 



direction of the deflection indicating a negative 

 charge. There is good reason to believe that the 

 charge is equal to that on the liquid ion, and hence, 

 from the measured values of the deflections, Sir J. 

 J. Thomson was able to calculate the mass of the 

 particles, as well as their velocities. 



In this way Thomson made the remarkable dis- 

 covery that, whatever be the residual gas or the 

 material of the electrodes, the mass of these cathode 

 particles was the same, and equal to about the eight- 

 hundredth part of the mass of the lightest atom 

 known to chemistry that of hydrogen. In these 

 ultra-atomic " corpuscles " the old conception of a 

 basis common to all types of matter has been realised 

 at length. 



The corresponding positively electrified rays, on 

 the other hand, proceeding from the positive elec- 

 trode, are never of less than atomic dimensions, but 

 consist of streams of electrified atoms or molecules 

 derived mainly from the gas left in the vessel. From 

 the magnetic and electric deflections, the atomic 

 weight of these positive carriers may be measured, 

 and thus the particles identified among the atoms 

 and molecules of chemical substances. 



The phosphorescence produced by the impact of 

 Rontgen rays on certain substances suggested that 

 these substances themselves might emit radiations. 

 In a search for such effects, Becquerel discovered 

 that salts of uranium emitted spontaneously rays 



