136 THE PATH OF SCIENCE 



showed no activity, so that it was concluded that these resi- 

 dues contained substances originally in the pitchblende that 

 were chemically very similar to barium and to bismuth. 

 These substances could be isolated by a long tedious process 

 of fractional crystallization, and w^hen it was carried out, new 

 elements were identified chemically. The one associated 

 with the barium was named radium^ and to the one found 

 with bismuth Madame Curie gave the name polonium^ from 

 her own country, Poland. 



If the scientific world had been startled by the discovery 

 of the x-rays and the identification of the electron, this dis- 

 covery was even more astonishing. Here for the first time 

 were chemical elements that were obviously unstable. The 

 radium salts w^ere visibly decomposing. In the process of 

 decomposition, they emitted (1) beta rays, that is, electrons; 



(2) gamma rays, which were soon shown to be x-rays; and 



(3) a new radiation of short penetrating power but of great 

 intensity, to which the name alpha rays w^as given. These 

 rays, when studied in a magnetic and an electric field, proved 

 to be streams of positively charged particles. The relation 

 of their mass to their charge showed that they had a mass 

 either twice that of hydrogen, that is, they had an atomic 

 weight of 2, or they were atoms of helium that had a weight 

 of 4 but carried two positive charges. Sir Ernest Rutherford, 

 whose name now comes into the story, showed that the par- 

 ticles were, indeed, doubly charged atoms of helium and that 

 they turned into helium by picking up negative electric 

 charges by collision wdth hydrogen atoms, the helium being 

 identified by the bright yellow line with w^hich it glows and 

 which can be seen in the spectroscope. 



The successive transformations of radium and polonium 

 were followed by chemists and physicists. It was sho^vn that 

 radium changes into several solids successively, and then into 

 a gas, which, in turn, changes into a solid and then into an- 

 other solid, and so on until, finally, the changes cease and a 

 stable atom of lead is produced. In this process, a series of ra- 

 diations are emitted— sometimes alpha rays, sometimes the 



