Earth as an Abode fitted for Life. 11 



great surface of liquid lava bounding the earth before 

 consolidation ; and of mountain heights and ocean depths 

 formed probably a few years after a first emergence of solid 

 rock from the liquid surface (see § 24, below) , which must have 

 been quickly followed by complete consolidation all round the 

 globe. But I must first ask you to excuse my giving you all 

 my depths, heights, and distances, in terms of the kilometre, 

 being about six-tenths of that very inconvenient measure the 

 English statute mile, which, with all the other monstrosities 

 of our British metrical system, will, let us hope, not long- 

 survive the legislation of our present Parliamentary session 

 destined to honour the sixty years'' Jubilee of Queen Victoria's 

 reign by legalising the French metrical system for the United 

 Kingdom. 



§ 23. To prepare for considering consolidation at the surface 

 let us go back to a time (probably not more than twenty 

 years earlier as we shall presently see — § 24) when the solid 

 nucleus was covered with liquid lava to a depth of several 

 kilometres ; to fix our ideas let us say 40 kilometres (or 4 

 million centimetres). At this depth in lava, if of specific 

 gravity 2*5, the hydrostatic pressure is 10 tons weight (10 

 million grammes) per square centimetre, or ten thousand 

 atmospheres approximately. According to the laboratory 

 experiments of Clarence King and Carl Barus * on Diabase, 

 and the thermodynamic theory f of my brother, the late 

 Professor James Thomson, the melting temperature of 

 diabase is 1170° C. at ordinary atmospheric pressure, and 

 would be 1420° under the pressure of ten thousand atmo- 

 spheres, if the rise of temperature with pressure followed the 

 law of simple proportion up to so high a pressure. 



§ 24. The temperature of our 40 kilometres deep lava 

 ocean of melted diabase may therefore be taken as but 

 little less than 1420° from surface to bottom. Its surface 

 would radiate heat out into space at some such rate as two 

 (gramme-water) thermal units Centigrade per square centi- 

 metre per second J. Thus, in a year (31J million seconds) 



* Phil. Mag. 1893, first half-year, p. 306. 



t Trans. Roy. Soc. Edinburgh, Jan. 2, 1849 ; Cambridge and Dublin 

 Mathematical Journal, Nov. 1850. Reprinted in Math, and Phys. Papers 

 (Kelvin), vol. i. p. 156. 



% This is a very rough estimate which I have formed from consideration 

 of J. T. Bottomley's accurate determinations in absolute measure of 

 thermal radiation at temperatures up to 9^0° C. from platinum wire and 

 from polished and blackened surfaces of various hinds in receivers of air- 

 pumps exhausted down to one ten-millionth of the atmospheric pressure 

 Phil, Trans. Roy. Soc, 1887 and 1893. 



