i9o8.] THE PHYSICS OF THE EARTH. 253 



paper " Zur Physik des Vulcanismus," published in 1900, Arrhenius 

 points out that in fluids at high temperature, where no increase in 

 vohnne takes place, the internal friction of the molecules rises with 

 the temperature, so that the viscosity increases and the fluidity 

 diminishes ; that a similar effect is observable in both gases and 

 liquids ; that although gases have the highest and solids the lowest 

 compressibility, nevertheless when a gas near its critical tempera- 

 ture passes into a liquid, through a trifling physical change, there 

 is practically no change in the compressibility. The higher the 

 pressure the smaller is the compressibility, and a gas above the 

 critical temperature may be made to acquire the properties of a 

 solid by pressure alone. Such a mass has great density, small com- 

 pressibility, and large viscosity, so that it has the properties of a 

 solid, though really an imprisoned gas. 



At a depth of 40 kilometers Arrhenius says the temperature is 

 about 1200° C, and the pressure about 10,840 atmospheres ; and 

 as these conditions would render nearly all ordinary minerals fluid, 

 he concludes that below that depth the matter is molten, in the 

 form of a magma — that is, a viscous and nearly incompressible 

 liquid made to act nearly as a solid by pressure. 



At greater depths the temperature is above the critical tempera- 

 ture of every known substance, as the pressure rapidly increases 

 and the liquid magma becomes a gaseous magma with larger and 

 larger viscosity, and smaller and smaller compressibility — in other 

 words, an elastic solid with rigidity increasing with the depth. 



VI. Abandonment of the Old Theories of the Physics of the 



Earth. 



§ 48. The Total Inadequacy of the Old Theories to Account for 

 the Fault Movements near the Sea, zvhich Raise Vertical Blocks and 

 Walls of Granite'^ Thousands of Feet above the Water. — The vast 



^ Andesite is the name used to designate the kind of granitic rock found 

 in the Andes. Charles Darwin showed that all granitic rocks are closely 

 related. In his " Text-book of Geology," edition of 1903, book II, Part II, 

 § 7, pp. 230-260, Sir Archibald Geikie gives tables of the chemical compo- 

 sitions of all these rocks, which show very clearly their close relationship. 

 When we use the term granite therefore we mean granitic rock in the wide 

 sense. 



PROC. AMER. PHIL. SOC. XLVH. 189 Q, PRINTED SEPTEMBER 24, I908. 



