118 MR. A. W. WATERS ON A CHANGE IN 



the equatorial bulge only moves the axis two or three 

 miles. 



This statement of Sir G. B. Airy has been used to see 

 what effect special alterations could have given^ and by 

 means of simple arithmetic. The results thus obtained 

 are roughly identical with the figures which have been 

 worked out exactly by Sir William Thomson* and by Mr. 

 G. H. DarwiUj M.A.fj in a paper read before the Royal 

 Society, of which only a tantalizing abstract has yet been 

 published, thus corroborating Sir G. B. Airy's figures. 



Mr. G. H. Darwin concludes that a single large geological 

 change, such as those which obtain on the earth, is com- 

 petent to produce an alteration in the position of the pole 

 of from one to three degrees of latitude. This is principally, 

 I presume, calculated from the efiect of distortion on the 

 position on the eartVs centre of gravity J . 



* Loc. cit. 



t Proc. Koyal Soc. No. 175, and 'Nature,' Feb. 22nd, 1877. 



X Since this paper was written ' Le deplacement Polaire ' of Dr. Jules 

 Garret has come into my hands. This little work is written to demonstrate 

 from various grounds that the position of the axis has changed, but without 

 inquiring into the cause. The greater part of the book is devoted to proving 

 that the present distribution of land and sea can only be explained by such 

 a change ; and this, he thinks, explains the polar land-area, and the antipodal 

 position of nearly all the land- to water-areas ; and he shows that the effect 

 of a change of position of the axis, with the unequal diameters of the earth, 

 which are unequally divided by the centre of gravity, will be to cause the 

 land to be antipodal to the water ; and the slight exceptions are near to the 

 circumference of an equator dividing the globe into land- and water-hemi- 

 spheres, which is where the exceptions would be expected. 



By these exceptions he concludes that the poles have moved in a curved 

 direction. If we divide the earth by a plane (grand cercle polaire) perpen- 

 dicular to the equator and to the direction in which the position of the poles 

 is changing, the points of intersection at the equator form two pivots for 

 this motion ; and here the effect of readjustment will be a minimum, while 

 before and behind will be an area of elevation and submergence respectively. 

 If the motion is curved, the plane (g. c. p.) we have just supposed must 

 cut the tangent of this curve at right angles. The changing position of the 

 tangent changes the position of the plane and of the points of intersection, 

 80 that points near the equatorial intersection are removed from the ele- 



