266 MODERN SCIENCE READER 



rupted atoms cease to be matter as ordinarily understood. 



The principle of the conservation of mass was heretofore 

 regarded as the corner-stone of the chemical edifice. It 

 assumed matter to be indestructible, and indestructible it 

 surely is by the time-honored methods of the laboratory. 

 Decomposition and recomposition, solution and precipita- 

 tion, fractionation, distillation, calcination, leave mass 

 exactly what it was before. Gravity is unalterable so long 

 as the atom remains intact. But the break-up of the atom 

 in radio-active processes lands us on a totally different 

 plane of inquiry. Atoms are composed of "electrons" or 

 unit-particles of electricity, linked together by forces of 

 tremendous power. When the infinitesimally small, though 

 highly intricate, systems thus formed undergo collapse 

 through some innate defect of stability, a readjustment 

 ensues. Some of their component electrons issue freely 

 into the ambient ether; others group themselves anew into 

 atoms of less heavy metals ; others again into helium-atoms. 

 But the total resulting atomic weight must be less than the 

 weight of the original, undecomposed atom, in consequence 

 of the subtraction of escaped electrons. Whether or no 

 electrons gravitate is a moot point. They possess inertia; 

 yet appear to lie outside the domain of the great universal 

 force. In shaking off atomic bonds they would then cease 

 to gravitate, and mass would be, pro tanto, diminished. 1 

 On the contrary supposition, there should be a loss, not of 

 absolute, but of measurable mass ; for electrons, once set at 

 large, are not easily recaptured. 



These still obscure, though significant possibilities illus- 

 trate the radical change in the views of physicists brought 

 to pass by the investigation of radio-activity. Once more, 

 as of old, the framework of nature has come to appear 

 plastic. Once more we are confronted with the quintes- 

 sential community of material things. We discern them 

 as built up variously out of the same sub-elemental stuff, 

 which, like the materia prima of the ancients, is subtilized 

 *E. Rutherford, Radio- Activity, second edition, page 336. 



