4 



(of which quartz is a familiar example) in combination chiefly with 

 potash. 



As regards the crust, we should have expected the composition 

 I have traced, from the gravity of its component parts alone, but we 

 have also corroborative evidence in the composition of the older 

 granites. 



" The process of solidification iu all probability commenced both 

 •at the centre and at the surface, leaving in the interior, vast 

 reservoirs of fluid igneous matter which are still supposed to exist, 

 the character of their molten contents however being variable." * 



It has been objected to this view, that as the surface cooled it 

 would sink into the fluid, molten matter from which it had 

 Bolidified, but we must remember that this cooling action would 

 take place simultaneously at all points, and we should have a 

 hollow sphere maintaining its shape by the cohesion of its 

 particles ; and again, although the effect of heat in the first 

 instance is to cause expansion, yet many substances 'contract again 

 as they become fluid, like iron, for instance, which when heated 

 would float on a surface of the same metal in a molten state. 



From our present knowledge of the law of gravity and of 

 physics generall}'', we are able to say with certainty that some such 

 state of things I have just sketched, must have existed, but on 

 the consideration that the earth was at this time a sun, and 

 accepting the astronomer's dictum that the probable past and future 

 of the sun are the probable past and future of every star in the 

 firmament, it is clear that if we had the power to make com- 

 parisons with existing suns, we should arrive at additional proof. 

 We have such power. If we take the present centre of our 

 system we shall find, so far as discovery has yet gone, how nearly 

 identical its condition now is to the condition of the earth at the 

 time we have been considering. Recent discoveries have not been 

 sufficiently established to enable us to speak with anything like 

 certainty of the body of the sun itself, and even of the photo- 

 sphere or true surface, we can only infer, of the latter, its cloudy 

 nature, and that the clouds are composed of particles of various 



• David Forbes, F.E.S. 



