200 PHYSICAL SCIENCE 



that are now at our disposal. As we have seen, 

 experimental evidence is not altogether wanting 

 in favour of such a supposition. We must, at any 

 rate, cease to regard matter as essentially eternal 

 and unalterable ; the possibility of its undergoing 

 a continual though slow process of disintegration 

 is clearly before us. 



A striking property of radio-active change is 

 our inability to produce it, or even to modify its 

 course, by any of the usual means within the 

 resources of modern physical science. The 

 highest temperature we can employ on the in- 

 tense cold of liquid air, the most complete 

 vacuum attainable on a pressure of a thousand 

 atmospheres, are equally useless. The observa- 

 tion that the activity of radium is independent 

 of the concentration of the material shows that 

 the disintegration of one part of this substance 

 is not accelerated by the radiation from another 

 part. Even under the fierce and continuous 

 bombardment of the atomic projectiles hurled 

 forth by radium, and the sharp musketry of its 

 corpuscular 1^ rays, the residual atoms of radium 

 are unaffected. They remain unchanged by the 

 action of any internal agency, till, in the fullness 

 of time, their own internal processes result in 

 instability, and, from the shattered fragments 

 of each radium atom, as, in its turn, it breaks 

 asunder, new elements emerge. 



But in 1922 Rutherford announced the result 

 of some experiments in which the atoms of certain 

 elements had been broken up by the bombard- 

 ment of a particles. Heavy atoms such as those of 

 radium seem to resist all such attempts, but with 

 some types of lighter atoms success was attained. 



