462 SCIENCE PROGRESS 



ford. The address was so full of pertinent and illuminating material that it 

 is most difficult to treat in the cursory manner necessary in this article. 

 Prof. Eddington first showed that we are more likely to get information from 

 the giant stars, on account of tlieir very low density. Such a star is to be 

 regarded as a vast storehouse of heat, of which, however, a large proportion 

 exists as radiant energy imprisoned by the particles. It is only those ether 

 waves which succeed in escaping through the material which represent energy 

 lost by the star. The next point dwelt on was the effect of the outward radia- 

 tion pressure, due to the non-escaping radiation, on the equilibrium of the 

 star. Prof. Eddington then proceeded to show how to calculate the absorp- 

 tion coefficient of stellar material, and announced the conclusion that the 

 penetrating power of the radiation is much the same as that of X-rays. 

 Other conclusions arrived at are that all giant stars lie between limits of 

 mass in the proportion 3:1, and that it is possible to calculate the periods 

 of variable stars, with results in fair accordance with experience. It is 

 possible also to apply the theory to the estimation of angular diameters of 

 stars, from direct consideration of their surface brightness. It is hoped 

 shortly to compare these estimates with measurements which the Mount 

 Wilson telescope seems likely to be capable of performing. Perhaps the 

 most interesting portion of the address was that in which Prof. Eddington 

 dealt with the source of the energy of stars. He threw over very definitely 

 the contraction-by-gravitation theory. A quotation will be appropriate. 

 " Only the inertia of tradition keeps the contraction hypothesis alive — or 

 rather, not alive, but an unburied corpse. But if we decide to inter the 

 corpse, let us frankly recognise the position in which we are left. A star is 

 drawing on some vast reservoir of energy by means unknown to us. This 

 reservoir can scarcely be other than the subatomic energy which, it is known, 

 exists abundantly in all matter. . . ." 



Prof. Eddington believes that the energy is supplied during the aggrega- 

 tion of hydrogen atoms to form other elements, and regards as significant 

 the discrepancy from the ratio 4 : i found in the masses of helium and hydro- 

 gen atoms. The deficit represents the mass of the electrical energy set free 

 when hydrogen transforms to helium. This is the only discrepancy j'^et found 

 by Dr. Aston, but with more refined measurements others may soon be 

 detected. Prof. Eddington appeared at the end of his address as an apologist 

 for speculation— a role which he filled with great brilliancy. His arguments 

 were a delightful mixture of truth and fun. 



Two interesting astronomical papers followed. Mr. J. Evershed read a 

 paper on the Measures of the Shifts of the Frauenhofer Lines and their Interpre- 

 tation, particularly with relation to the Einstein Theory. The results of his 

 extensive work at the Kodaikanal Observatory, India, must still be regarded 

 as inconclusive in relation to the theory in question. Mr. Evershed referred 

 especially to his elegant method of observing the lines in the sunlight reflected 

 from Venus. In this case he finds the resultant shifts which are observed 

 in direct sunlight to be absent. This is in opposition to Einstein's prediction, 

 which would apply equally to light leaving the sun in all directions. 



Sir F. Dyson gave a short description of the new star discovered by 

 Mr. Denning in Cygnus on August 19. The magnitude was then increasing, 

 and the spectrum was the same as that of a Cygni. On August 26 Prof. A. 

 Fowler was able to extend the information by exhibiting slides of the 

 spectrum taken by Dr. Lockyer on August 21, and subsequent days. The 

 development of the spectral arrangement appeared to be following the same 

 course as Nova Aquilae (19 18). 



The rest of the morning was occupied by mathematical papers by 

 Prof. H. Hilton and Mr. T. C. Lewis. 



On August 25 the chief papers were by Dr. F. W. Aston and Sir Ernest 

 Rutherford. Dr. Aston gave a lucid description of his positive ray measure- 



