8o SCIENCE AND IMMORTALITY 



may be likened in some respects to the condensa- 

 tion and contraction of a nebula. The particles 

 constituting a whirling nebula fall together until 

 the centrifugal force of the peripheral portions 

 exceeds the gravitative pull of the central mass, 

 and then they are shrunk off and left behind, 

 afterwards agglomerating into a planet, while the 

 residue goes on shrinking and evolving fresh 

 bodies and generating heat. A nebula is not hot, 

 but it has an immense store of potential energy, 

 some of which it can turn into heat, and so form a 

 hot central nucleus or sun. A radium atom is 

 not hot ; but it, too, has a great store of potential 

 energy, immense in proportion to its mass, for it is 

 controlled by electrical, not by gravitational forces ; 

 and just as the falling together of the solar 

 material generates heats, so that a shrinkage of a 

 few yards per century can account for all its 

 tremendous emission, so it has been calculated 

 that the collapsing of the electrical constituents of 

 a radium atom by so little as one per cent, of their 

 distance apart can supply the whole of the energy 

 of the observed radiation — large though that is — 

 for something like thirty thousand years." 



This is a most interesting comparison, and 

 numerous other astronomical comparisons may be 

 made. Thus it has been found possible to perturb 

 the orbits of the corpuscles in atoms. 



