The Rev. J. A. Coombe oti the Rotation of the Earth. 555 



of this question have been advanced by different writers. Still 

 there is difficulty, if not doubt, left upon the minds of many 

 persons, to whom a lucid explanation of the phsenomenon would 

 be a great relief and gratification. It is for the assistance of 

 such indi\dduals that I have attempted in this paper a threefold 

 solution of the problem ; the two first being perhaps more strict 

 and geometrical, the last more popular. In pi-inciple these solu- 

 tions would be found identical with each other, as well as with 

 those that have been proposed by other writers. The varied form 

 under which they appear wall, it is hoped, recommend them 

 to cbfferent classes of readers. 



The nature of the experiment itself I need hardly describe, as 

 the details of it are so generally known. In explaining the 

 rationale of this interesting phsenomenon — 



I. Let us look upon it, in the first place, in the light of a 

 strictly dynamical problem. 



Let CP (fig. 1) be the axis Fig. I. 



about which the earth (consi- 

 dered here as a sphere) rotates 

 with an angular velocity =a). 



Let A be the place of obser- 

 vation in latitude \. 



Let J)Q,d be the horizontal 

 circular table (centre A) over 

 which the pendulum suspended 

 at K oscillates, and which may 

 be considered identical with 

 the surface of the earth around 

 A. 



Let PA be the meridian, in 

 which, for the sake of simpli- 

 city, we will su^ppose the pendulum to be oscillating at the 

 moment under consideration. 



Join CA, and draw CB in the plane PCA perpendicular to CA. 



Now as the table revolves about the axis CP, it may be con- 

 sidered as partaking, at this instant, of three separate and inde- 

 pendent motions about three rectangular axes parallel to its prin- 

 cipal axes, — 



viz. about CA perpendicular to the plane of the table ; 

 about CB parallel to the plane of the table ; 

 about a third axis through C pei-pendicular to the plane 

 of the paper ; 

 which will be parallel to a line drawn through A perpendicular 

 to Till in the plane of the table. 



Now there is evidently, from the nature of the motion, no ten- 

 dency to rotate about the third axis ; because the plane of the 

 table always intersects the axis CP in one point, which is, as it 

 3P2 



