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Intelligence and Miscellaneous Articles. 323 



ON SEA-LEVELS. 



To the Editors of the Philosophical Magazine and Journal. 



Kitlands, Dorking, 

 Gentlemen, March 24, 1866. 



I hope you can afford me space in your forthcoming Number to 

 announce and correct a serious blunder in my paper on " Sea-levels." 



Starting, as I did, I should have treated the excess of matter in 

 the nucleus, equally with the ice-cap, as extraneous to the homoge- 

 neous spheroid of which I was determining the form only. 



The term in B would then have disappeared spontaneously from 

 my equation ; and its value, or the depth southward to which the 

 nucleus will be sunk by the downward pressure of the ice-cap, 

 would have to be determined by considering that, for equilibrium, 

 there must be no tendency to relative motion between the rigidly- 

 connected disturbing bodies and the homogeneous spheroid. And 

 this would in fact be just to reinstate into the expression for 



Idx + Ydy+Zdz) 



the two terms in Q x which had been previously expunged, equating 



their sum to zero*. 



The result is, that the rise of water (above the mean level of the 



then existing sea), measured from the centre of the nucleus, w r ould 



3 B 

 be that calculated in my paper + 1- A 1 Q , or, with my nume- 



(0 — 1 z 



rical data, 375 cos N.P.D. in feet. Thus we obtain at the north pole 

 a rise of 1078 feet instead of 703 ; at the south pole, a fall of 206 

 feet instead of a rise of 169 ; at latitude 55° N., a rise of 387 feet 

 instead of 80 ; at latitude 55° S., a fall of 194 feet instead of a rise 

 of 113. D. D. Heath. 



THE AXTAL ROTATION OF THE EARTH. 

 BY J. S. STUART GLENNIE, M.A., F.R.A.S. ETC. 



To the Editors of tjie Philosophical Magazine and Journal. 

 Gentlemen, 



I observe that in the current Number of your Magazine Pro- 

 fessor F. Guthrie proposes the hypothesis that " the earth revolves 

 on its axis in the same direction as its orbital rotation," in conse- 

 quence of its "side nearest the sun" encountering "aether of 

 greater density than is met with by the remoter side." 



I beg to say that in the Philosophical Magazine for April 1861, 

 p. 277 et seq., I had already stated, and applied to the case of the 

 planetary (axial) rotations, the theorem that, " according as the 

 resultant of a resisting medium passes, or not, through the centre 

 of gravity of a revolving body, is it an accelerating force of revolu- 

 tion, or a partially neutralized accelerating force of rotation." 



This theorem seemed to me of importance because of the general 

 assumption that a resisting medium should affect the (orbital) revo- 



* It is the same ceremony that Laplace goes through in respect of the 

 actions of the particles of the spheroid itself on one another and on the 

 centre : Liv- 3. ch. 4. No. 23 ; and again in the Theory of the Tides. 



