The Rev. J. A. Coombe on the Rotation of the Earth. 559 



the table may have about BAd in passing from one position to 

 an adjacent one, of this motion K and the plane of vibration 

 equally participate. Hence the effect to a spectator will be the 

 same as before, and the plane of vibration will appear to revolve 



round the table in the time -: hours. 



sm X 



III. The third mode of exhibiting the reason of this phseno- 

 menon is a more popular one. 



At the north and south poles the case is clear enough. The 

 centre of the table being fixed cUrectly over the pole of the earth, 

 will be stationary, while the table itself, being carried round by 

 the earth's rotation, ^^411 rotate about that centre once in twenty- 

 four hours. The pendulmn swinging freely over this centre will 

 continue to vibrate in its original dii-ection, and thus the plane 

 of vibration will appear to revolve once in twenty-four hours. 

 At the equator, on the other hand, the table is carried round its 

 daily circle, always retaining the same relative position to the 

 plane of Aabration : a given diameter in it always remains parallel 

 to itself, and hence the line of nbration will appear to be sta- 

 tionarjf. 



For intermediate latitudes, I suppose the reader to have a 

 common globe before him. Let him fix his eye upon the parallel 

 of latitude in which we are situated. If a piece of coin, a shil- 

 ling for instance (head uppermost), be now firmly attached to 

 this globe at any point of this parallel of latitude, with the face 

 looking towards the north, that is along the meridian line, and 

 the globe be now turned upon its axis, this will form a correct 

 representation of the horizontal table, in the experiment, carried 

 round by the earth's rotation. In this motion the face of the 

 shilling would be always turned towards a fixed point in the pro- 

 longation of the axis of the globe. The effect of this is evidently 

 the same as if the centre of the shilling were fixed, and it was 

 made to turn round that centre as upon a pivot, for the motion 

 of the face of the shiUing would be the same in both cases. So 

 also a person looking along the north line of the horizontal table 

 would have the eye constantly directed to a fixed point in the 

 earth's axis ; and the effect of this would be the same as if the 

 centre of that table were stationary, and the table turned round 

 its centre as upon an axis. Now be it remarked, that the 

 plane of the pendulum does not participate in this motion, any 

 more than a smooth marble moving upon a smooth table would 

 participate of any rotatory motion which that tal)le might have 

 about its own centre in its own plane. It is true tlu; |)lane of 

 vibration has a motion, arising from the motion of the ])oint of 

 Huspension; but the table participates equally of this; and the 

 effect of this motion is only to keep the plane of vibration always 



