THE FUEL OF THE SUN. 89 



which is, u The Varying Splendor of Different Portions of 

 the Photosphere."* 



But I must not linger any further upon this part of the sub- 

 ject, but proceed to another, where subsequent discoveries 

 have strongly confirmed my speculations. 



The mean specific gravity of the sun is not quite 1-J- times 

 that of water. The vapors of nickel, cobalt, copper, iron, 

 chromium, manganese, titanium, zinc, cadmium, aluminium, 

 magnesium, barium, strontium, calcium, and sodium have been 

 shown by the spectroscope to be floating on the outer regions 

 of the sun. None of these could constitute the body of the 

 sun in a solid or liquid state, and be subjected to the enormous 

 pressure which such a mass must exert upon itself without 

 raising the mean specific gravity vastly above this ; nor is there 

 any other kind of matter with which we are acquainted which 

 could exist within so large a mass in a liquid or solid state, 

 and retain so low a density. 



I must confess that my faith in the logical acumen of mathe- 

 maticians has been rudely shaken by the manner in which 

 eminent astronomers have described the umbra or nucleus of 

 the sun-spots as the solid body of the sun seen through his 

 luminous atmosphere, and the solid surface of Jupiter seen 

 through his belts, and have discussed the habitability of 

 Jupiter, Saturn, Uranus, and Neptune always on the assumption 

 of their solidity, while the specific gravity of all of these 

 renders this surface solidity a demonstrable physical impossi- 

 bility. 



If the sun (or either of these planets) has a solid or liquid 

 nucleus, it must be a mere kernel in the centre of a huge orb 

 of gaseous matter, and though I have spoken rather definitely 

 of the solar atmosphere in order to avoid complication, I must 

 not, therefore, be understood to suppose that there exists in 

 the sun any such definite boundary to the base of the atmos- 

 pheric matter as we find here on the earth. The temperature, 

 the density, and all we know of the chemistry of the sun justi- 

 fy the conclusion that in its outer regions, to a considerable 

 depth below the photosphere, there must be a commingling of 

 the atmospheric matter with the vapors of the metals whose 

 existence the spectroscope has revealed. Some of these must 

 be upheaved together with the dissociated elements of water. 



* Still more recently (1882) the magnificent photographs of 

 Jannsen have displayed further evidence of the flame-tongue charac- 

 ter of the mottling. 



