THE PLAN OF THE EARTH AND ITS CAUSES. 375 



his predecessor, Green assumes that the earth is a spheroid based on a 

 regular geometrical figure. He adopted as his base the apparently 

 hopelessly unsuitable figure of the tetrahedron, which is contained 

 within four equal similar triangles. This form, with its four faces, six 

 sharp edges, and four solid corners, does not conform to the ordinary 

 conception of the figure of the globe. Any comparison between them 

 looks ridiculous. But if we place a three-sided pyramid on each side 

 of the tetrahedron, its proportions are nearer those of a globe; and if 

 these pyramids had elastic sides, so that they could be blown out and 

 the faces thus made curved, then the tetrahedron would become sphe- 

 roidal and even spherical. Conversely, if a hollow sphere be gradually 



Fig. 5. 



5a, DIAGRAM OP A SIMPLE TETRAHEDRON.— 5b, DIAGRAM OF A TETRAHEDRON WITH A SIX-FACED PYRA- 

 MID WITH CONVEX FACES ON EACH OF THE FOUR FACES.— 5c, THE TRACE OF THE TETRAHEDRAL 

 EDGES ON A SPHEEE; THE THICK LINES SHOW THE POSITION OF THE TETRAHEDRAL EDGES. 



exhausted of air, the external pressure may force in the shell at four 

 mutually equidistant points, and, by the flattening of these four faces, 

 make it tend toward atetrahedral form. Now thetetrahedral theory does 

 not regard the world as a regular tetrahedron with four plane faces. It 

 considers that the lithosphere has been subjected to a slight tetrahe- 

 dral deformation, to an extent indeed only faintly, if at all, indicated 

 by geodetic measurements, but yet easily recognizable owing to its 

 influence on the distribution of land and water. As the centers of the 

 flattened faces are nearer the earth's center of mass than the edges, the 

 water will collect upon them. The ratio of the area of land to that of 

 water on the globe is as 2 to 5. If on a model of a tetrahedron we color 

 the five-sevenths of the surface that is nearest the center, the colored 



