Lieber 



conditions are actually made, i.e., historically developed. This is the deeper 

 meaning of stability, in the sense that the flow field that actually develops by a 

 particular historical process is the most stable among the flows admitted by the 

 Navier -Stokes equations, which do not imply a unique flow, and the maintained 

 boundary conditions. According to the thesis of the present paper, the evolution 

 of stable flows accords with the principle of maximum uniformity. 



Geophysical Aspects of Evolution 



The search for a primary seismic driving force, i.e., a force that causally 

 drives earthquakes on a global scale, is as old as the science of geophysics and 

 has been a most important challenge to the mind. The mechanical aspects of 

 geophysics have been and are being considered primarily from the standpoint of 

 the established laws of classical mechanics which are supposed to be complete 

 in their application to the mechanics of the earth, and thus to contain all the in- 

 formation necessary for answering all questions that concern the mechanical 

 nature and behavior of the earth. This point of view has been applied equally in 

 the search for a primary seismic driving force, and explains, I believe, why 

 such a force has not been identified until comparatively recently. The reason is 

 that such a force is a direct consequence of an evolutionary mechanical process, 

 which it in part motivates, and the fact that the laws of classical mechanics as 

 they are known, are in principle devoid of historical content and therefore of in- 

 formation that concerns evolution as a process in a mechanical system, such as 

 the earth. Therefore, the answer to the question put at the beginning of this sec- 

 tion is simply not contained in the laws of classical mechanics to which man 

 turned for the answer. The answer is evidently in the principle of maximum 

 uniformity. A primary seismic driving force was discovered by the author on 

 the basis of this principle about two years ago, and was specifically identified 

 with the earth's rotation, which provides its primary source of energy. The 

 idea that led to its conception is simple, once the principle of maximum uni- 

 formity is brought into consideration. The rotation of the earth impresses a 

 global nonuniformity on the earth, which is physically expressed by the nonuni- 

 formity in the local and global distribution of forces that its rotation produces 

 in conjunction with the nonuniformities of the figure of the earth, of its mechani- 

 cal constitution, and of the nonuniform spatial distribution of its inertial mass. 

 A necessary condition required for the development of this primary seismic 

 driving force is that the earth be inelastic and that it accordingly accommodate 

 relaxation phenomena which may progressively lead to reduction of shear 

 stress — shear stress being interpreted here as a local and fundamental aspect 

 of local nonuniformity of the force field around an element of material. The 

 states of stress produced in a fluid in hydrostatic equilibrium are free of shear 

 stress and consequently are states in which imiformity is everywhere locally 

 maximized. When the primary seismic -tectonic force presented here is con- 

 sidered in relation to a mechanical model of the earth's crust and mantle, which 

 ascribes to the very upper mantle a thin layer of visco-elastic material of com- 

 paratively low viscosity and high mobility, then according to the principle of 

 maximum uniformity, forces will develop that cause the material to flow with 

 velocity components that are parallel as well as perpendicular to the surface of 

 the earth. This motion in the layer induces horizontal forces on the ocean floor 

 that would cause spreading of the continents; but since the direction of the 



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