3 68 POPULAR SCIENCE MONTHLY. 



C. ; even if we call it only 15,000°, we should expect to find there 

 only gases, and those in a simple state, for with that heat all the com- 

 pound gases would be dissociated. The zone of fluidity for all rocks 

 lies at a depth of about one hundred kilometres, where the tempera- 

 ture is 2,500° C. While the crust of the earth is between 2.5 and 

 three times as heavy as distilled water at 4° C, its specific gravity 

 rises toward the center of the earth to more than eleven, or about 

 fourfold. Iron has a specific gravity of 7.8, or about threefold that of 

 the crust of the earth; but the specific gravity of the earth at the 

 greatest depth is considerably higher than this. Hence must arise 

 an enormous pressure, steadily increasing toward the center, where, 

 according to the English geophysicist, the Rev. Osmond Fisher, it 

 reaches about three million atmospheres to the English square inch. 

 It results from these conditions that with the enormous pressure and 

 heat, and specific gravity, the interior of the earth consists of dissoci- 

 ated gases compressed to great rigidity, which exert an immense 

 counter-pressure — for their tendency is always to expand. They pass 

 out continuously into a zone of fluid matter, and this again is held by 

 the pressure of the interior gases in a like compact condition. Thus 

 a very high pressure still prevails in the lower parts of the solid crust 

 of the earth, which is so high that even the most solid rocks there 

 are in a latent plastic condition — that is, they behave toward differ- 

 ent forces like plastic clay, and like it can be deformed without break- 

 ing. Rents, slides, caves, and clefts are out of the question there; 

 things of that kind can exist only in the upper strata. 



This fact constitutes a very strong objection to the tectonic theory 

 of earthquakes, and thus the very depths of the earth speak against 

 it. We have already mentioned that K. von Seebach estimated the 

 depth of the earthquake focus from the movements of the waves, 

 and found it not very great. But his estimates, as Prof. August 

 Schmidt has shown, rest upon physically incorrect premises; accord- 

 ing to Schmidt's more correct calculation, the center of the Charles- 

 ton earthquake of 1886 lay at a depth of one hundred and twenty 

 kilometres, where there can be no question of tectonic movements, 

 because general fluidity is reached at one hundred kilometres. Fur- 

 ther, the earthquake at Lisbon, if the tectonic theory is valid, might, 

 taking the character of the region into consideration, have been occa- 

 sioned by a slide. But how large must the plunging mass, how deep 

 the plunge or slide have been to produce such shocks as destroyed 

 Lisbon and shook Europe to beyond Bohemia! Where can we find 

 room in the closely compressed interior of the earth for such irrup- 

 tions? Even if such a sudden sinking had left no trace in the in- 

 terior, it should have left its marks on the surface. Mr. John Milne 

 counts up not less than 8,331 considerable earthquake shocks in 



