230 Master Minds of Modern Science 



Rutherford, who have spent their lives in difficult and 

 patient investigation. 



The atomic theory was first given to the world by 

 Dalton more than a century ago ; the electron was dis- 

 covered by Professor J. J. Thomson in 1897 ; but it has 

 remained for Sir Ernest Rutherford, working with Dr 

 Geiger and others, actually to break up an atom and to 

 put forward the theory of the proton or charged centre. 



To break up an object so small that you cannot see it 

 seems rather a tall order, and the more so when it is an 

 object hitherto believed to be indivisible. The very word 

 ' atom ' implies something that cannot be divided. Sir 

 Ernest knew that whatever weapon he employed would 

 have to be very powerful. His thoughts turned to 

 radium, the strange element on which he had already done 

 a great deal of work since its discovery by the Curies. 



Radium, as you know, is so called because it is radio- 

 active. It is unstable, and has the peculiar property of 

 breaking up and constantly discharging extremely small 

 particles. Sir Ernest came to the conclusion that the 

 most powerful projectiles which he could possibly employ 

 were the so-called alpha-particles which radium is always 

 discharging. 



Some readers may have seen the living picture of 

 radium rays which was originally taken in the Cavendish 

 Laboratory at Cambridge. The room is darkened, and on 

 the screen appears a snow-storm of tiny sparks of light 

 which come and go like snow-flakes falling on the surface 

 of a stream. These travel at the almost incredible speed 

 of eighty thousand miles a second. 



The first experiment Sir Ernest made consisted of 

 driving numbers of these alpha-particles into a vessel 

 filled with nitrogen gas. This was shooting at random, 

 and he could not know in advance whether any of his tiny 

 bullets would do the job he proposed for them. But they 

 did. He found that one in about ten million collided 



