36 SECTIONAL ADDRESSES. 



is the true order of continuous increase of density, which was hidden 

 by superficial resemblances. 



The giant stars, representing the first half of a star's hfe, are 

 taken as material for our first boring experiment. Probably, measured 

 in time, this stage corresponds to much less than half the life, for 

 here it is the ascent which is easy and the way down is long and slow, 

 Let us try to picture the conditions inside a giant star. We need not 

 dwell on the vast dimensions — a mass hke that of the Sun, but swollen 

 to much greater volume on account of the low density, often below 

 that of our own atmosphere. It is the star as a storehouse of heat 

 which especially engages our attention. In the hot bodies famihar to 

 us the heat consists in the energy of motion of the ultimate particles, 

 flying at great speeds hither and thither. So too in the stars a great 

 store of heat exists in this form; but a new feature arises. A large 

 proportion, sometimes more than half the total heat, consists of 

 imprisoned radiant energy — ether-waves travelling in all directions 

 trying to break through the material which encages them. The star 

 is like a sieve, which can only retain them temporarily ; they are turned 

 aside, scattered, absorbed for a moment, and flung out again in a new 

 direction. An element of energy may thread the maze for hundreds 

 of years before it attains the freedom of outer space. Nevertheless the 

 sieve leaks, and a steady stream permeates outwards, supplying the 

 light and heat which the star radiates all round. 



That some ethereal heat as well as material heat exists in any hot 

 body would naturally be admitted; but the point on which we have 

 here to lay stress is that in the stars, particularly in the giant stars, 

 the ethereal portion rises to an importance which quite transcends our 

 ordinary experience, so that we are confronted with a new type of 

 jjroblem. In a red-hot mass of iron the ethereal energy constitutes 

 less than a billionth part of the whole ; but in the tussle between matter 

 and ether the ether gains a larger and larger proportion of the energy 

 as the temperature rises. This change in proportion is rapid, the 

 ethereal energy increasing rigorously as the fomih power of the tem- 

 perature, and the material energy roughly as the first power. But even 

 at the temperature of some millions of degrees attained inside the stars 

 there would still remain a great disproportion ; and it is the low density 

 of material, and accordingly reduced material energy per unit volume 

 in the giant stars, which wipes out the last few powers of 10. In all 

 the giant stars known to us, widely as they differ from one another, the 

 conditdons are just reached at which these two varieties of heat-energy 

 have attained a rough equality; at any rate one cannot be neglected 

 compared with the other. Theoretically there could be conditions in 

 which the disproportion was reversed and the ethereal far out-weighed 

 the material energy; but we do not find them in the stars. It is as 

 though the stars had been measured out — that their sizes had been 

 determined — with a view to this balance of power; and one cannot 

 refrain from attributing to this condition a deep significance in the 

 evolution of the cosmos into separate stars. 



To recapitulate. We are acquainted with heat in two foi-ms — the 

 energy of motion of material atoms and the energy of ether waves. In 



