162 Scientific Intelligence. 



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 

 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 

 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 centimeter per second.* 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 aban- 

 doned by a million cubic centimeters of melted diabase in solidi- 

 fying 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 experimentsf 

 of 100 years ago, when more than a few minutes is taken for the 

 freezing, the solid formed is not a glass but a heterogeneous crys- 

 talline 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 diabase is 14 per 

 cent denser than melted diabase, and 10 per cent denser than the 

 glass produced by quick freezing of the liquid. He gives no 

 data, nor do Rticker and Roberts-Austen, who have also experi- 

 mented on the thermodynamic properties of melted basalt, give 

 any data, as to the latent heat evolved in the consolidation of 

 liquid lava into rock of basaltic quality. Guessing it as three 

 times the latent heat of fusion of the diabase pitch-stone, I esti- 

 mate a million cubic centimeters of liquid frozen per square cen- 

 timeter per centimeter per three years. This would diminish the 

 depth of the liquid at the rate of a million centimeters per three 

 years, or 40 kilometers in twelve years." 



"§25. Let us now consider in what manner this diminution of 

 depth of the lava ocean must have proceeded, by the freezing 

 of portions of it; all having been at temperatures very little 

 below the assumed 1420° melting temperature of the bottom, 

 when the depth was 40 kilometers. The loss of heat from the 

 white-hot surface (temperatures from 1420° to perhaps 1380° in 

 different parts) at our assumed rate of two (gramme-water Centi- 

 grade) thermal units per sq. cm. per sec. produces very rapid 

 cooling of the liquid within a few centimeters of the surface 



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

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

 tion 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 tenth-millionth of the atmospheric pressure. Phil. Trans. Roy. Soc, 1887 

 and 1893. 



f Trans. Roy. Soc. Edinburgh. 



