382 POPULAR LECTURES AND ADDRESSES. 



maintained by the paddle ; and after a few hours 

 or days, solidification would commence at the 

 surface. If the solidified matter floats on the 

 fluid, at the same temperature, below it, the crust 

 would simply thicken as ice on a lake thickens in 

 frosty weather ; but if, as is more probable, solid 

 matter, of such ingredients as the sun is composed 

 of, sinks in the liquid when both are at the melting 

 temperature of the substance, thin films of the 

 upper crust would fall in, and continue falling in, 

 until, for several metres downwards, the whole 

 mass of mixed solid and fluid becomes stiff enough 

 (like the stiffness of paste or of mortar) to prevent 

 the frozen film from falling down from the surface. 

 The surface film would then quickly thicken, and 

 in the course of a few hours or days become less 

 than red-hot on its upper surface, the whole pit 

 full of fluid would go on cooling with extreme 

 slowness until, after possibly about a million 

 million million years or so, it would be all at the 

 same temperature as the space to which its upper 

 end radiates. 



Let precisely what we have been considering 



