38 THI: CIIKMISTRY OF THE PRIMEVAL EARTH. [iv. 



supposed to be maintained by the slow condensation of its mass ; 

 a diminution by TtAroth f iks present diameter being sufficient, 

 according to Helmholtz, to maintain the present supply of heat 

 for 21,000 years. 



This hypothesis of the nature of the sun and of the luminous 

 process going on at its surface is the one lately put forward by 

 Faye, and, although it has met with opposition, appears to be 

 A Inch accords best with our present knowledge of the 

 chemical and physical conditions of matter such as we must 

 suppose it to exist in the condensing gaseous mass, which, 

 according to the nebular hypothesis, should form the centre 

 of our solar system. Taking this, as we have already don 

 granted, it matters little whether we imagine the different 

 planets to have been successively detached as rings during the 

 rotation of the primal mass, as is generally conceived, or 

 whether we admit with Chacornac a process of aggregation or 

 concretion operating within the primal nebular mass, resulting 

 in the production of sun and planets, "in either case we come 

 to the conclusion that our earth must at one time have been in 

 an intensely heated gaseous condition, such as the sun now pre- 

 . self-luminous, and with a process of condensation going 

 on at first at the surface only, until by cooling it must have 

 reached the point where the gaseous centre was exchange 

 one of combined and liquefied matter. 



Hi-re commences the chemistry of the earth, to the discussion 

 of which the foregoing considerations have been only j .n-lim- 

 inary. So long as the gaseous condition of the earth lasted, 

 we may suppose the whole mass to have been homogeneous ; 

 but whi-n the t.'inperature became so reduced that t lie existence 

 of chemical compounds at the centre became possible, those 

 \vlii.hweremoststableat the elevated temperature then pre- 

 vailing would be first formed. Thus, for example, while corn- 

 Is of oxygen with mercury, or even with hydrogen, could 



s of silicon, aluminum, calcium, magnesium 

 jaL'lit be formed and condense in a liquid form at the 

 centre of the globe. By progressive cooling, still other el. : 

 would be removed from the gaseous mass, which would form 



