380 THE PLAN OF THE EARTH AND ITS CAUSES. 



difference. The whole, in fact, in this case was less than the sum of its 

 parts. 



To astronomers it may seem an unnecessary waste of time to devote 

 so much to proving these deformations from the " spheroid of reference." 

 But as the idea is less familiar to geographers and geologists, the 

 insistence of this deformation may not be useless. It may be worth 

 while adding a quotation from Prof. C. A. Young, 1 to show that the 

 spheroid of reference is only a convenient assumption. " On the whole," 

 says Professor Young, "astronomers are disposed to take the ground 

 that since no regular geometrical solid whatsoever can absolutely repre- 

 sent the form of the earth, we may as well assume a regular spheroid 

 for the standard surface, and consider all variations from it as local 

 phenomena, like hills and valleys." 



As deviations from the assumed spheroid of reference exist, it remains 

 to inquire whether there is any evidence that they agree in position 

 and arrangement with the theory of the tetrahedral deformation of 

 the lithosphere. 



The evidence already quoted of the dissimilarity between the northern 

 and southern hemispheres and the elongation of the latter, is geodetic 

 proof of the northern flattening and the antarctic projection, i. e., of 

 one face and one tetrahedral corner. 



The three flattened lateral faces and three projecting vertical edges 

 are sufficiently demonstrated by the three great oceans and the land- 

 lines that divide them. Practically, all the theories agree upon that 

 point. It is well known that gravity is greater than was expected at 

 most oceanic islands. Lallemand and de Lapparent have suggested 

 that this is due to those islands being below the level of the ordinarily 

 accepted figure of the earth, and therefore nearer the earth's center of 

 gravity. 2 Fisher has suggested that the Pacific Ocean is the hollow 

 left by the loss of the material which forms the moon. Faye has 

 explained the ocean basins and the greater density of the crust below 

 them as due to more rapid refrigeration below the cold oceanic abysses. 

 According, therefore, to Faye, the rocks below the oceans contracted 

 more than those below the continents, became denser, and accordingly 

 sank. 



Thus from all points of view the three oceans represent areas of 

 depression, and the three land lines of South America, Africa, and 

 Australasia mark intervening projections. The oceans mark the low 

 areas in the lithosphere as obviously as the bubble of a spirit level 

 marks its higher end; and they give, therefore, evidence of the trian- 

 gular lateral flattening of the southern half of the globe. 



But as, on the mathematical figure of the earth, such lateral flatten- 



1 C. A. Young, General Astronomy, p. 101. 1889. 



2 This explanation i.s inadequate, as it does not explain the deviation of the pendu- 

 lum on coast line toward the ocean. The excess vertical attraction of the islands 

 has been explained as due to the attraction of the mass of the island and its base. 



