158 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1923 



the formation of the alpha particle would mean that, in forming it, 

 energy would be liberated, which would have to be put back into 

 it again in order to separate the parts. The calculated amount of 

 energy is so enormously great that it is not at all surprising that the 

 alpha particle is so stable. Even in the collisions with other atomic 

 nuclei which shatter the latter into fragments, the forces (which can 

 be roughly calculated) are not nearly strong enough to disintegrate 

 it. 



We may now suppose that, in the interior of the stars, and by 

 some process the details of which are still quite unknown, the atoms 

 of hydrogen are taken apart, and the pieces — protons and electrons — 

 built up into the nuclei of heavier atoms, with just enough elec- 

 trons left over to build the outer parts of these. We can not be 

 sure, of course, that such a thing actually happens; but if it does, 

 the energy liberated will suffice for the present demands of astro- 

 physics. If the sun, for example, was originally all hydrogen, 

 which was transformed in this fashion into other elements, the 

 energy which would be set free as a by-product would keep it 

 shining at the present rate for about 120 billions of years. 



Such is our present conception of the stars, their distance, their 

 age, their nature, and their life history. In the grandeur of its 

 sweep in space and time, and the beauty and simplicity of the re- 

 lations which it discloses between the greatest and the smallest 

 things of which we know, it reveals as perhaps nothing else does, 

 the majesty of the order about us which we call nature, and, as I 

 believe, of that Power behind the order, of which it is but a passing 

 shadow. 



