SECTION A : CAEDIFF, 1920. 



ADDRESS 



TO THE 



MATHEMATICAL AND PHYSICAL SCIENCE SECTION 



BY 



Peofessor a. S. EDDINGTON, M.A., M.Sc, F.K.S., 



PEESIDENT OF THE SECTION. 



The Internal Constitution of the Stars. 



Last year at Bournemouth we listened to a proposal from the President 

 of the Association to bore a hole in the crust of the earth and discover 

 the conditions deep down below the surface. This proposal may 

 remind us that the most secret places of Natm'e are, perhaps, not 

 10 to the n-th miles above our heads, but 10 miles below our feet. 

 In the last five years the outward march of astronomical discovery has 

 been rapid, and the most remote worlds are now scarcely safe from 

 its inquisition. By the work of H. Shapley the globular clustei-s, which 

 are found to be at distances scarcely dreamt of hitherto, have been 

 explored, and our knowledge of them is in some respects more com- 

 plete than that of the local aggregation of stars which includes the Sun. 

 Distance lends not enchantment but precision to the view. Moreover, 

 theoretical researches of Einstein and Weyl make it probable that the 

 space which remains beyond is not illimitable; not merely the 

 material universe, but space itself, is perhaps finite; and the explorer 

 must one day stay his conquering march for lack of fresh realms to 

 invade. But to-day let us turn our thoughts inwards to that other 

 region of mystery — a region cut off by more substantial barriers, for, 

 contrary to many anticipations, even the discovery of the fourth 

 dimension has not enabled us to get at the inside of a body. Science 

 Eas material and non-material appliances to bore into the interior, and 

 I have chosen to devote this address to what may be described as 

 analytical boring devices — absit omenl 



The analytical appHance is delicate at present, and, I fear, would 

 make little headway against the solid crust of the earth. Instead of 

 letting it blunt itself against the rocks, let us look round for something 

 easier to penetrate. The Sun? Well, perhaps. Many have struggled 

 to penetrate the mystery of the interior of the Sun ; but the difficulties 

 are great, for its substance is denser than water. It may not be quite 

 6o bad as Biron makes out in Love's Labour's Lost: — 



The heaven's glorious sun, 



That will not be deep-searched with saucy looks; 



Small have continual plodders ever won 



Save base authority from others' books. 



