REVIEWS 463 



matter changes its state from solid to liquid, and from liquid to gas. If, for 

 instance, we wished to apply a pressure which would reduce surface rock to 

 the density 3, it ought to be 5.9X10'' (9 — 2.75^) = 8.481 X lo'^ pounds per 

 square foot, supposing no heat be allowed to escape. If the experiment 

 could be made, it would afford a test of the truth or otherwise of the present 

 hypothesis. 



When we know the relation between the pressure and the condensation 

 which it would produce, it is feasible to estimate the heat which would be 

 generated, and also the temperature, provided we assume the specific heat 

 of the substance, which for surface rock has been determined. For instance, 

 at the depth of o.i of the radius, or about 400 miles deep, where the density 

 would be 3.88, the temperature produced by condensation would be 1.2608 X 

 10® Fahr., or 7.0044 X 10* Cent. [70,044°], while at the center the figures 

 would reach 2.7756 X 10^ Fahr., or 1.0242 X 10® Cent. [1,024,200°]. It 

 seems at any rate that the meteoric theory would not fall short of accounting 

 for temperatures as high as might be desired. It must at the same time be 

 remembered that much of this heat would not be called into existence until 

 the substance into which it was, as it were, being squeezed, had already been 

 deeply buried under a badly conducting covering, so that the escape of heat 

 would not take place as fast as it was generated, as would probably be the 

 case with heat generated at the suface by impacts. Thus the hypothesis that 

 the present high internal temperatures are due to compression seems quite 

 admissible. 



We may compare the above named temperatures with some that are 

 known. Acheson, for instance, obtains 6500" Fahr. in his Carborundum elec- 

 tric furnace, and 3300° Fahr. has been obtained by the oxyhydrogen flame. 

 These temperatures are contemptible compared with those mentioned above. 

 The Hon. Clarence King, prolonging Dr. Barus' line for the melting point of 

 diabase (which is 1 170° C. at the earth's surface) to the earth's center, gives 

 the temperature 76000" Cent., which is of the same order of magnitude as 

 condensation would produce at only 400 miles depth. 



Fisher considers the bearing of the temperature of lava as deter- 

 mined by Bartoli at Etna (io6o°C. or 1932° F.) on the question, and 

 finds that the theoretical depth at which this lava tetnperature would 

 be produced by condensation would be about forty-three miles. The 

 same temperature would be reached at the accepted gradient of 1° F. 

 for sixty feet in about twenty-two miles. 



It seems then that the hypothesis, that the internal densities are due to 

 the condensation of matter of surface density, will not account for a tempera- 

 ture gradient originally as high as at present. [The computed gradient cor- 

 responds pretty nearly with the low gradient found at the Calumet and Hecla 



