May 12, 1899.] 



SCIENCE. 



673 



close up to the surface ; except compara- 

 tively small portions of lava or melted rock 

 among the solid masses of denser solid rock 

 ■which had sunk through the liquid, and 

 possibly a somewhat larger space around 

 the center occupied by platinum, gold, 

 silver, lead, copper, iron and other dense 

 metals, still remaining liquid under very 

 high pressure. 



§ 22. I wish now to speak to you of 

 depths below the 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 a complete con- 

 solidation all around the globe. But I 

 must first ask you to excuse my giving you 

 all my depths, heights and distances, in 

 terms of the- kilometer, being about sis- 

 tenths of that very inconvenient measure 

 the English statute mile, which, with all 

 the other monstrosities of our British met- 

 rical 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 consoli- 

 dation 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 kilometers; 

 to fix our ideas let us say 40 kilometers (or 

 4 million centimeters). At this depth in 

 lava, if of specific gravity 2.5, the hydro- 

 static pressure is 10 tons weight (10 million 

 grammes) per square centimeter, or ten 

 thousand atmospheres approximately. Ac- 

 cording to the laboratory experiments of 

 Clarence King and Carl Barus* on Diabase, 



* Philosophical Magazine, 1893, first half-year, p. 

 .306. 



and the thermodynamic theory* 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 atmospheres, if the rise of tem- 

 perature with pressure followed the law of 

 simple proportion up to so high a pressure. 



§ 24. The temperature of our 40 kilo- 

 meters deep lava ocean of melted diabase 

 may therefore be taken as but little less 

 than 1420° from surface to bottom. Its 

 svirface would radiate heat out into space 

 at some such rate as two (gramme-water) 

 thermal units Centigrade per square centi- 

 meter per second. t Thus, in a year (31^ 

 million seconds) 63 million thermal units 

 would be lost per square centimeter from 

 the surface. This is, according to Carl 

 Barus, very nearly equal to the latent heat 

 of fusion abandoned by a million cubic cen- 

 timeters of melted diabase in solidfying into 

 the glassy condition (pitch-stone) 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 experi- 

 ments:j: of 100 years ago, when more than a 

 few minutes is taken for the freezing, the 

 solid formed is not a glass but a hetero- 

 geneous 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 Barus finds that basaltic 



* Trans. Eoy. Soc, Edinburgh, .Tan. 2, 1849; Cam- 

 bridge and Dublin Jlaihematical Journal, Nov. , 1850. 

 Reprinted in Math, and Phys. Papers (Keh'in), Vol. 

 I., p. 156. 



t This is a very rough estimate which I have formed 

 from consideration of J. T. Eottomley's accurate de- 

 terminations in absolute measure of thermal radiation 

 at temperatures up to 920° C. from platinum wire 

 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. Eoy. Soc, 1887 and 1893. 



j Trans. Eoy. Soc. Edinburgh. 



