AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 347 



depths, lieiglits, and distances in terms of the kilometer, 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 parlia- 

 mentary session, destined to honor the sixty years' jubilee of Queen 

 Victoria's reign by legalizing 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 wit'h liquid 

 lava to a depth of several kilometers; to fix our ideas let us say 40 kilo- 

 meters (or 4,000,000 centimeters). At this depth in lava, if of specific 

 gravity 2.5, the hydrostatic pressure is 10 tons weight (10,000,000 

 gram) per square centimeter, or 10,000 atmospheres approximately. 

 According to the laboratory experiments of Clarence King and Carl 

 Barns ^ on diabase, and the thermodynamic theory^ of my brother, the 

 late Prof. James Thomson, the melting temperature of diabase is 1,170"^ 

 C. at ordinary atmospheric pressure, and would be 1,420° under the 

 I)ressure of 10,000 atmospheres, 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 kilometers deep lava ocean of melted 

 diabase may therefore be taken as but little less than 1,420° from sur- 

 face to bottom. Its surface would radiate heat out into space at some 

 such rate as 2 (gram-water) thermal units centigrade per square centi- 

 meter per second.^ Thus, in a year (31,500,000 seconds) 03,000,000 

 thermal units would be lost per square centimeter from the surface. 

 This is, according to Carl Barns, very nearly equal to the latent heat of 

 fusion abandoned by a million cubic centimeters of melted diabase in 

 solidifying into the glassy condition (pitchstone) which is assumed 

 when the freezing takes place in the course of a few minutes. But, as 

 found by Sir James Hall in his Edinburgh experiments^ of one hundred 

 years ago, when more than a few minutes is taken for the freezing, the 

 solid formed is not a glass but a heterogeneous crystalline solid of rough 

 fracture; and if a few hours or days, or any longer time, is taken, the 

 solid formed has the well-known rough crystalline structure of basaltic 

 rocks found in all parts of the world. Now, Carl Barns finds that basaltic 

 diabase is 14 per cent denser than melted diabase and 10 per cent 



1 Phil. Mag., 1893, first half year, page 306. 



-Trans. Roy. Soc, Edinburgh, January 2, 1849 ; Cambridge and Dublin Mathemati- 

 cal Journal, November, 1850. Reprinted in Math, and Fhys. Papers (Kelvin), Vol. I, 

 page 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 920° C. from platinum vrire and from polished and blackened 

 surfaces of various kinds in receivers of air pumps exhausted down to one ten- 

 millionth of the atmospheric pressure. Phil. Trans. Roy, Soc, 1887 and 1893, 



■•Trans. Roy. Soc, Edinburgh. 



