THE FIGURE OF THE EARTH 



13 



continents has been secured in other fields. It was pointed out 

 that the earth's oblateness was proven by comparison of the 

 measured degrees of latitude upon the earth's surface in lower and 

 higher latitudes, the degree being found longer as the pole is 

 approached. Any variation from the spherical surface must ob- 

 viously increase the size of the measured degree of latitude in 

 proportion to the departure from the standard form, and so 

 the tetrahedral figure with one of its angles at the south pole 

 will require that the degrees 

 of latitude be longer in the 

 southern than they are in the 

 northern hemisphere. This 

 has been found by measure- 

 ment to be the case, and the 

 result is further confirmed by 

 pendulum studies upon the 

 distribution of the earth's at- 

 traction or gravity. If less of 

 the mass of the earth is con- 

 centrated in the southern 

 hemisphere, its attraction as 

 measured in vibrations of 

 the pendulum should be cor- 

 respondingly smaller. 



FIG. 4. A truncated tetrahedron, showing 

 how the depression upon one side of the cen- 

 ter is balanced by the opposite projection. 



Other confirmations of the tetrahedral figure of the earth have 

 been derived from a comparison of astronomical data, which assume 

 the earth to be a perfect spheroid, with geodetic measurements, 

 which are based upon direct measurements. Thus the arc meas- 

 ured in an east-and-west direction across Europe revealed a differ- 

 ent curvature near the angle of the tetrahedral figure from what 

 was found farther to the eastward. 



Changes of figure during contraction of a spherical body. If 

 we inquire why the earth in cooling should tend to approach the 

 tetrahedral figure, an answer is easily found. When formed, 

 the earth appears to have been a but slightly oblate spheroid, 

 or practically a sphere the shape which of all incloses the 

 most space for a given surface. Cooled and solidified at the sur- 

 face to the temperature of the surrounding air, and the core 

 still hot and continuing to lose heat, the core must continue to 



