176 Some Properties of the a. Rays from Radium. 



actions of the a rays with the property of producing ions 

 raises the question whether photographic and phosphorescent 

 effects in general may not, in the first place, be due to a 

 production of ions in the substance. 



Rayless Changes. 



The results already discussed show that the a particles from 

 the radioactive substances are projected with an average 

 velocity not more than 30 per cent, greater than the critical 

 velocity, below which the a particles are unable to produce 

 any ionizing, photographic, or phosphorescent action. Such 

 a conclusion suggests that the property of the radioactive 

 substances of emitting a rays has been primarily detected in 

 these substances because the a particles were projected slightly 

 above this critical velocity. A. similar disintegration of matter 

 may be taking place in other substances at a rate much 

 greater than in uranium, without producing much electrical 

 effect, provided the a particles are projected below the critical 

 velocity. 



The a particle, on an average, produces about 100,000 ions 

 in the gas before it is absorbed, so that the electrical effects 

 observed are about 100,000 times as great as those due to the 

 charge carried by the a particles alone, when the velocity 

 falls below the critical value. 



It is not unlikely that the numerous rayless products which 

 have been observed may undergo disintegration of a similar 

 character to the products which obviously emit a rays. In 

 the rayless product, the a particle is expelled with a velocity 

 less than 1*5 X 10 9 cms. per second, and so fails to produce 

 much electrical effect. 



These considerations have an important bearing on the 

 question of whether matter in general is radioactive. The pro- 

 perty of emitting a rays above the minimum velocity required 

 to produce ionization in the gas may well be a property only 

 of a special class of substances, and need not be exhibited by 

 matter in general. At the same time, the results suggest 

 that ordinary matter may be undergoing transformation 

 accompanied by the expulsion of a particles at a rate much 

 greater than uranium, without producing appreciable electrical 

 or photographic action. 



McGill University, Montreal, 

 May 8, 1905. 



