CONSTITUTION OF THE STARS— EDDINGTON 139 



physicists buzzing about my ears — but I don't think I have been 

 stung yet. Anyhow, for the purposes of this lecture, I will assume 

 that I haven't dropped a brick. 



I venture to refer to a personal aspect of this investigation, since it 

 shows how closely different branches of science are interlocked. At 

 the time when my suspicion of the relativistic degeneracy formula 

 was roused by Chandrasekhar's results, it was very inconvenient to 

 me to spare time to follow it up, because I was immersed in a long 

 investigation in a different field of thought. This work, which had 

 occupied me for 6 years, was nearing completion and there remained 

 only one problem, namely, the accurate theoretical calculation of the 

 cosmical constant, needed to round it off. But there I had completely 

 stuck. I had, however, secured a period of 4 months free from dis- 

 tractions which I intended to devote to it — to make a supreme effort, 

 so to speak. But having incautiously begun to think about the 

 degeneracy formula I could not get away from it. It took up my 

 time. The months slipped away, and I had done nothing with the 

 problem of the cosmical constant. Then one day in trying to test 

 my degeneracy results from all points of view, I found that in one 

 limiting case it merged into a cosmical problem. It gave a new 

 approach to the very problem which I had had to put aside — and 

 from this new approach the problem was soluble without much diffi- 

 culty. I can see now that it would have been very difficult to get at 

 it in any other way; and it is most unlikely that I should have made 

 any progress if I had spent the 4 mouths on the direct line of attack 

 which I had planned. 



The paper which I read to the mathematical section a few days 

 ago,^ giving a calculation of the speed of recession of the spiral nebulae 

 and the number of particles in the universe, had an astronomical 

 origin. It was not, however, suggested by consideration of the spiral 

 nebulae. It arose out of the study of the companion of Sirius and 

 other white dwarf stars. 



I mentioned that we only gradually came to realize that ionization 

 could be produced by high pressure as well as by high temperature. 

 I think the first man to state this explicitly was D. S. Kothari. Stim- 

 ulated by some work of H. N. RusseU, Kothari has made what I 

 think is an extremely interesting application. The relation of ioniza- 

 tion to pressure is a curious one, for at low pressures we decrease the 

 ionization by increasing the pressure; but the ionization must have a 

 minimum, for at high pressures the Fermi-Dirac complication steps 

 in and the ionization ultimately increases with pressure. No one 

 seems to have bothered much about this revised ionization law; they 

 have been content to recognize, or I think rather to guess, that in 

 white dwarfs the ionization would be pretty high. Kothari, how- 



> Amer. Journ. Math., vol. 59, no. 1, 1937. 



