ASTRONOMY OF THE NINETEENTH CENTURY. 



439 



plane, preserving as It would a fixed direction in space, would appear 

 to an observer to turn slowly in the direction of the hands of a watch 

 at the rate of 15 per hour, in consequence of everything but the plane 

 of oscillation being carried round by the earth in its rotation. If such 

 a pendulum were set in motion at other places on the surface, the 

 like apparent change in the plane of rotation would be observed ; but 

 its rate would be less and less as the plane was more distant from the 

 pole and nearer to the equator. Thus, while at the pole the plane 

 of rotation appears to turn through a complete circle in twenty-four 

 hours, in latitude 54 twenty-eight hours nearly would be required; 



