iv The Earth a Spinning Ball 55 



with regard to objects outside the ship all the while, and the 

 real motion of the deck toward the right gives an apparent 

 motion of the passenger toward the left. The same thing 

 is true of everything moving rapidly on the surface of the 

 rotating Earth, whether the moving body be a shot from a 

 cannon, a railway train, a river, or simply wind. This fact 

 is thus stated by the American meteorologist, Professor 

 Ferrel : If a body moves in any direction on the EartWs 

 surface, there is a deflecting force arising from the Earttts 

 rotation, which deflects it to the right in the northern 

 hemisphere, but to the left in the southern hemisphere. 

 The moving body has a tendency to keep on in a straight 

 line ; it is the Earth that changes its direction, as in Foucault's 

 pendulum experiment. Fig. 10 represents the apparent 

 deviation of a body moving in the southern hemisphere, 

 Fig. 1 1 that in the northern the thin arrow showing the 

 original direction, the thick arrow the deviation. 



90. Position of the Axis. The axis of the Earth about 

 which it rotates is the shortest diameter ( 82). If the 

 Earth was once much hotter than now and in a semi-fluid 

 condition (as we shall" subsequently see reasons to believe), 

 the mere fact of its rotation would make it bulge out along 

 the line farthest from the poles, and that to the precise degree 

 which is found to be the case. As in the case of the rapidly 

 spinning gyroscope ( 51), and for the same reason, the axis 

 of the Earth preserves its direction practically unchanged in 

 space ; and consequently the ends of the axis always point 

 to opposite parts of the starry sky. As the Earth rotates, 

 these points the poles of the heavens appear to be at 

 rest, while the sky with its constellations Appears to revolve 

 round them from east to west. The north pole of the Earth 

 points very nearly to a bright star which has received the 

 name of the Pole Star or Polaris, and is of the greatest 

 importance as a guide to direction and position on the 

 Earth in the northern hemisphere. 



9 1 . Direction on the Earth. On account of the Earth's 

 rotation it is possible to fix direction and position on its 

 surface. The line which we may imagine to be traced 

 round the Earth equally distant from both poles is termed 



