26 EVOLUTION 



may call a moderate temperature for the stellar world. 

 The gases of the nebula or the meteorites of the great 

 swarm whichever theory one follows are gathering 

 closer together, and the temperature is rising to 

 thousands of degrees from the colossal friction. In the 

 hottest stars the process of condensation has produced 

 its maximum heat, which may safely be conceived at 

 something over 10,000C. The chemical elements in it 

 are found to be actually dissociated in that appalling 

 furnace. At a later stage the electrons close again into 

 atoms; the various metals re-unite, and a layer of 

 molten metal thousands of miles thick forms the surface 

 of the star. The vapours of the metals lie above this 

 layer, and more thousands of miles of red-hot gas, with 

 a cooler atmosphere hundreds of thousands of miles deep 

 envelop the whole. As the loss of heat continues to be 

 greater than the production of it, the cooler vapours 

 thicken round the molten photosphere. Great black 

 patches (sun-spotsin reality wide oceans of cooler 

 vapour in which our earth could swim freely) appear on 

 the disc. The light to a distant observer sinks from 

 white to yellow, and as the vapours grow denser, to red. 

 Dark-red suns, of which we know many, point to a 

 further stage in the choking of the luminous centre. In 

 time, as we shall see in the last chapter, all the vapours 

 will turn to liquid, the liquid to solid, and a dark crust 

 will form round the condensed remainder of the nebula. 

 The only difference that we need note here in the case 

 of our sun is that it is a solitary star. A comparatively 

 small nebula has crystallised into one great luminary 

 with a number of much smaller satellites. This seems 

 to be an exceptional occurrence. Double stars seem to 

 be the rule in the heavens ; triple stars are common, and 

 even much more complex systems known. The 2,326 

 stars of the Pleiades cluster seem to have formed, in the 



