Earth as an Abode fitted for Life. 85 



after the freezing of the granitic interstitial mother liquor at 

 the earth's surface in any locality, the average temperature 

 at the surface might be warmer, by 60° or 80° Cent., than if 

 the whole interior had the same average temperature as the 

 surface. To fix our ideas, let us suppose, at the end of one 

 year, the surface to be 80° warmer than it would be with no 

 underground heat : then at the end of 100 years it would be 

 8° warmer, and at the end of 10,000 years it would be '8 of 

 a degree warmer, and at the end of 25 million years it would 

 be *016 of a degree warmer, than if there were no under- 

 ground heat. 



§ 39. When the surface of the earth was still white-hot 

 liquid all round, at a temperature fallen to about 1200° Cent., 

 there must have been hot gases and vapour of water above 

 it in all parts, and possibly vapours of some of the more 

 volatile of the present known terrestrial solids and liquids, 

 such as zinc, mercury, sulphur, phosphorus. The very rapid 

 cooling which followed instantly on the solidification at the 

 surface must have caused a rapid downpour of all the vapours 

 other than water, if any there were ; and a little later, rain 

 of water out of the air, as the temperature of the surface 

 cooled from red heat to such moderate temperatures as 40° 

 and 20° and 10° Cent., above the average due to sun heat 

 and radiation into the aether around the earth. What that 

 primitive atmosphere was, and how much rain of water fell 

 on the earth in the course of the first century after consoli- 

 dation, we cannot tell for certain ; but Natural History and 

 Natural Philosophy give us some foundation for endeavours 

 to discover much towards answering the great questions,— 

 Whence came our present atmosphere of nitrogen, oxygen, 

 and carbonic acid ? Whence came our present oceans and 

 lakes of salt and fresh water ? How near an approximation 



radiational eniissivity of rock and atmosphere of gases and watery vapour 

 above it radiating- heat into the surrounding vacuous space -(aether), we 

 find 8000 X -005, or 40 degrees Cent, as the excess of the mean surface 

 temperature above what it would be if no heat were conducted from 

 within outwards. The present augmentation of temperature downwards 

 may be taken as 1 degree Cent, per 27 metres as a rough average derived 

 from observations in all parts of the earth where underground temperature 

 has been observed. (See British Association Reports from 1868 to 1895. 

 The very valuable work of this Committee has been carried on for these 

 twenty-seven years with great skill, perseverance, and success, by 

 Professor Everett, and he promises a continuation of his reports from 

 time to time.) This with the same data for conductivity and radiational 

 emissivity as in the preceding calculation makes 40°/2700 or 00118 u Cent. 

 per centimetre as the amount by which the average temperature of the 

 earth's surface is at present kept up by underground heat. 



