MIRACLES OF SCIENCE 



ality atoms of helium each carrying a double charge 

 of positive electricity. 



The beta ray is identical with the cathode ray 

 which develops when electricity is passed through 

 a Crookes' or vacuum tube. 



The gamma ray is identical with the X-ray which 

 is developed when a cathode ray strikes the walls of 

 the glass receptacle. It is due to the impingement 

 of beta rays on the particles of the radioactive sub- 

 stance itself, and it probably constitutes a pulsation 

 in the ether of a kind analagous to the waves of light 

 and electro-magnetism. 



The alpha ray has been studied with great care 

 and it has given up one secret after another. That 

 the alpha particle is an atom of helium, is a startling 

 fact. For helium is an element hitherto known as an 

 inert constituent of the atmosphere. And to suppose 

 that one element can be transformed into another 

 is to suggest a restoration of the obsolete heresy of 

 the alchemist. Nevertheless the demonstration is 

 complete that the alpha ray does consist of helium 

 atoms, and that it is precisely the same whether it 

 emanates from thorium, from radium, or from any 

 other known radioactive substance however the 

 fact may be explained. 



COUNTING THE ATOMS 



Of the many theoretical and practical considera- 

 tions that attend the subject none perhaps has a 

 greater interest than the experiments which have 

 made it possible to isolate an individual atom and 

 actually test its size. 



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