1867.] HUNT THE CHEMISTRY OF THE EARTH. 227 



however, that notwithstanding its excessive temperature, it has a 

 specific gravity not much below that of water ; probably offering 

 a condition analogous to that which Cagniard de la Tour observed 

 for volatile bodies when submitted to great pressure at tempera- 

 tures much above their boiling point. The radiation of heat, 

 going on from the surface of such an intensely heated mass of 

 uncombined gases, will produce a superficial cooling, which will 

 permit the combination of certain elements and the production of 

 solid or liquid particles, which, suspended in the still dissociated 

 vapours, become intensely luminous and form the solar photo- 

 sphere. The condensed particles, carried down into the intensely 

 heated mass, again meet with a heat of dissociation ; so that the 

 process of combination at the surface is incessantly renewed, while 

 the heat of the sun may be supposed to be maintained by the slow 

 condensation of its mass; a diminution by T o\roth of its 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 that 

 which 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 done, for 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 presents, 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 were the gaseous centre was exchanged for one 

 of combined and liquefied matter. 



Here commences the chemistry of the earth, to the discussion 

 of which the foregoing considerations have been only prelimiuaiy. 

 So long as the gaseous condition of the earth lasted, we may 

 suppose the whole mass to have been homogeneous ; but when the 

 temperature became so reduced that the existence of chemical 



