The Groundwork of the Universe, Sec. 53 



Eecall now the three types of ray from the Crookes' tube, the 

 Cathode-ray, the Positive-ray, and the X-ray. Each of these has 

 the same qualities as one of the constituents of tlie Becquerel 

 rays, corresponding as below : — 



]jecquerel Raj's. Crookes' Tulles. 



Alpha-rays, Positive-rays, 



Beta-rays, Cathode-rays, 



Gramma-rays, X-rays. 



The Alpha-rays are atoms of helium, each atom carrying two 

 charges of positive electricity ; the Beta-rays are streams of 

 negative electrons, while the Gamma-rays are really X rays having 

 a penetrating power far in excess of any we can produce arti- 

 ficially. Some idea of the enormous velocities of emission may 

 be got from the following figures : — 



Alpha particles ... 20,000 miles per second. 



Beta „ ... 170,000 „ 



Light ... 186,000 „ 



A little reflection will suggest the reason of the phenomena 

 observed in radio-active centres. The Alpha particle, ejected from 

 the radio-active atom at a very high velocity soon strikes some 

 heavier matter in the form of atoms in the radio-active mass and 

 heat is thus generated, so that these helium atoms will tend to raise 

 the temperature of the material with which they collide, and keep 

 it permanently above that of surrounding bodies. Again, radio- 

 active materials eject showers of electrons travelling much faster 

 than the Alpha particles. When these strike matter they generate 

 X-rays, as the cathode stream of a Crookes' tube did at its point 

 of contact with the glass, so that there is a complete parallel 

 between the action of the Becquerel rays and that of the Crookes' 

 tube. 



To sum up the properties exhibited by the Becquerel rays as 

 a whole — They have the power of ionizing gases and making 



