

m 



I 



412 



iJei;. C ^. Lyman on the Pendulum Experiment. 



equator, where both the meridians and successive positions of the 

 pendulum plane maintain a perpetual parallelism. 



This varying rate of relative angular motion as we proceed 

 from the poles to the equator, may be very simply illustrated by 

 the following easy device. 



Cut out a circular piece of paper, and draw radii from its cen- 

 ter to every thirtieth degree, as represented in the figure. At the 

 extremities of these radii draw a series of arrows, all parallel to 

 each other around the entire circle. Cut open the paper from the 

 center outwards, as at the double line in the figure. 



This paper with its radii may be used to represent the cone form- 

 ed by the meridional tangents, having the axis of the earth passing 

 up through its apex or center, and its base resting on a parallel of 

 latitude. At the pole, where the tangents touch the surface of the 

 earth, and all lie in the same plane, the suni of all the angles 

 which they form at the center, is equal to 360, as represented by 

 the paper in its original flat condition, its circumference being en- 



T _x _ pendulum be carried around the Dole at an indefinitely 



tire. 



small distance from it, say a few feet only, and the successive po- 

 sitions of its plane of vibration will be not only relatively paral- 



lel to each other, but may be considered as strictly so, as repre 

 setited by the arrows in the figure. If now one edge of the i^- 

 per where it is cut open, be Jipped over the other, the center will 

 rise and form the apex of a cone : and as one edge of the paper, 





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