Foundations of the Universe 259 



5 



The Discovery of the Electron 



Physicists did not take long to discover that the radiation 

 from radium was very like the radiation in a "Crookes tube." It 

 was quickly recognised, moreover, that both in the tube and in 

 radium (and other metals) the atoms of matter were somehow 

 breaking down. 



However, the first step was to recognise that there were 

 three distinct and different rays that were given off by such metals 

 as radium and uranium. Sir Ernest Rutherford christened 

 them, after the first three letters of the Greek alphabet, the Alpha, 

 the Beta, and Gamma rays. We are concerned chiefly with the 

 second group and purpose here to deal with that group only. 1 



The "Beta rays," as they were at first called, have proved to 

 be one of the most interesting discoveries that science ever made. 

 They proved what Crookes had surmised about the radiations 

 he discovered in his vacuum tube. But it was not a fourth state 

 of matter that had been found, but a new property of matter, a 

 property common to all atoms of matter. The Beta rays were 

 later christened Electrons. They are particles of disembodied 

 electricity, here spontaneously liberated from the atoms of mat- 

 ter: only when the electron was isolated from the atom was it 

 recognised for the first time as a separate entity. Electrons, 

 therefore, are a constituent of the atoms of matter, and we have 

 discovered that they can be released from the atom by a variety 

 of agencies. Electrons are to be found everywhere, forming part 



of every atom. 



''An electron," Sir William Bragg says, "can only maintain 

 a separate existence if it is travelling at an immense rate, from 

 one three-hundredth of the velocity of light upwards, that is to 



' The "Alpha rays" were presently recognised as atoms of helium gas, shot out at 

 the rate of 12,000 miles a second. 



The "Gamma rays" are waves, like the X-rays, not material particles. They ap- 

 pear to be a tvpe of X-rays. They possess the remarkable power of penetrating 

 opaque substances; they will pass through a foot of solid iron, f< 



