JoLY — Radiant Matter. 75 



been established. In 1906 Rutherford showed that the a rays from all sorts 

 of radioactive bodies are alike in mass; and he gave tlie strongest reasons for 

 believing that they are, in fact, helium atoms in an electrified state. He 

 showed tliat these radiant atoms carry a positive charge, and suggested then, 

 what he has since more fully established, that this charge is in quantity 

 double that which monad atoms carry wlien ionized. No more fundamental 

 discoveries in the science of matter liave ever been made. 



The consideration of Sir J. J. Tliomson's beautiful method of determining 

 the mass and velocity of such elusive objects as are carried in these 

 invisible streams of radiant matter, by observing the effect of electric and 

 magnetic forces upon their direction of motion, would require not less than 

 the greater part of the time allotted to me. Their chemical nature once 

 determined gives us, however, their mass directly from our previous 

 knowledge of the element. 



Rutherford's final proof that those rays are lielium atoms is based upon 

 their power, while they are in the radiant state, of penetrating a thin screen 

 of solid matter. Tlie gaseous body derived from radium, the emanation, is 

 one of the radioactive elements, which, in the act of transmutation, gives out 

 a rays. Rutherford compressed some of this gas into a glass tube, so thin 

 tltat the a rays could dart through its walls, just as we found they penetrated 

 a thin mica plate. Surrounding this thin tube was a second tube in which 

 the spent a rays collected, as bullets wliich have dropped behind a target. 

 After some time a spectroscopic test of the contents of the outer tube showed 

 a brilliant helium spectrum. The proof is complete that these rays are 

 helium. Other evidence also exists. One most interesting fact must be 

 mentioned. Wherever in the rocks radioactive bodies are found — and they 

 are almost ubiquitous — there helium is also found. It probably represents 

 the stored-up a rays. 



The extraordinary phenomenon of the passage of tliese atoms through 

 solid screens finds its explanation in the liigh velocity with which radiant 

 matter is projected from radioactive substances. Their speed, as a material 

 speed, is by far the greatest known. It may amount to as mucli as 13,000 

 miles per second. That is to say, an a ray if unimpeded in its flight would 

 circulate round the earth in less than two seconds. The greatest material 

 velocity previously recorded is that of matter projected from the surface of 

 the sun when violent disturbances take place in his highly heated gases. 

 Velocities up to 500 or 600 miles per second have been in this case 

 surmised. 



Once we recognize the enormous speed of the a ray, we are rather 

 inclined to change our point of view, and wonder less at the penetration of 



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