26 SCIENCE IN SHORT CHAPTERS. 



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

 subject, but proceed to another, where subsequent discov- 

 eries have strongly confirmed my speculations. 



The mean specific gravity of the sun is not quite 1 

 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 con- 

 stitute 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 

 mathematicians 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 

 tnrough his luminous atmosphere, and the solid surface of 

 Jupiter seen through his belts, and have discussed the 

 habitability of Jupiter, Saturn, Uranus, and Neptune al- 

 ways on the assumption of their solidiy, while the specific- 

 gravity of all of these renders this surface solidity a dem- 

 onstrable physical impossibility. 



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

 uid 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, 1 must not, therefore, be understood to sup- 

 pose that there exists in the sun any such definite bound- 

 ary to the base of the atmospheric matter as we find here 

 on the earth. The temperature, the density, and all we 

 know of the chemistry of the sun justify the conclusion 

 that in its outer regions, to a considerable depth below the 

 photosphere, there must be a commingling of the atmos- 

 pheric matter with the vapors of the metals whose exist- 

 ence the spectroscope has revealed. Some of these must 

 be upheaved together with the dissociated elements of wa- 



