502 JOSEPH BARRELL 



tion of water into the heated rocks the conditions for volcanic 

 activity are initiated. This argument, Hke the others, is in the 

 form of a great extension or extrapolation of factors operative in 

 a small way in the laboratory to conditions in nature which are 

 wholly different in magnitude. 



As comments upon this paper, it should be noted that nearly 

 every conclusion applying to the sun and earth may be questioned. 



At a depth of i,oookm., according to Arrhenius, the temperature 

 is about 30,000° C. The gradient is thus taken as essentially a 

 straight line from the surface downward. There is no demon- 

 stration as to why this rectilinear extension is assumed, whether 

 it is to be regarded as an adiabatic temperature curve produced by 

 condensation under pressure or produced in some other way. The 

 influence of cooling through geologic time in changing the outer 

 gradient is not considered; nor the influence of rising magmas. 

 The existence of radioactivity was then just beginning to be appre- 

 ciated and naturally could not have been evaluated, but the data 

 for a discussion of the other factors, though at hand, was neglected. 



There is no' demonstration that the heavy elements are con- 

 centrated in the sun's interior, or that the earth is mostly metallic 

 iron. It is possible that the earth is thus constituted, but it must 

 be proved on better evidence than a citation of the dominance of 

 iron in nature. The incompressibihty of all substances, both 

 fluid and liquid, increases greatly with great increase of pressure, 

 following apparently parabolic curves. Therefore, it cannot be 

 argued with any assurance that the high incompressibihty of the 

 earth's interior proves the presence of iron, or that under such 

 pressures the fluid occupies less volume than the solid state. 



At a depth of 1,000 km. Arrhenius states that the temperature 

 is about 30,000° C. and the pressure 250,000 atmospheres.' If, 

 under these conditions of exalted temperatures, gaseous rock or 

 iron has a viscosity equal to that of solid steel it may well be asked 

 how the stars, with their immensely greater masses and consequent 

 internal pressures, can maintain a convective circulation compe- 

 tent to keep up their enormous surface radiation. Furthermore, 

 however viscous a compressed gas or liquid may be, this property 



' Op. cit., p. 400. 



