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SCIENCE 



[N. S. Vol. XXVII. No. 697 



citations from the co-tidal charts recently 

 issued by the U. S. Coast and Geodetic 

 Survey. Attention was called to certain 

 anomalies in the relative heights and pe- 

 culiar behavior of the tides which render 

 difficult any explanation on the usual lines, 

 and Harris's theory of their essential origin 

 in special segments of the oceans was briefly 

 sketched. In addition to this, an inertia 

 tide, assigned to the tilting of the basins 

 by the tidal deformation of the lithosphere, 

 was suggested as a supplementary possibil- 

 ity, but its quantitative value was not esti- 

 mated or urged. 



The normal oscillations of the earth as a 

 spheroid were briefly discussed in the light 

 of mathematical deductions and of certain 

 seismic, nutational and tidal phenomena, 

 with the general conclusion that the litho- 

 spheric pulsations, whether tidal or other- 

 wise, have a short period and, in the case 

 of the tides, act directly with the forcing 

 agency. 



An attempt to analyze and estimate the 

 influence of the water tides as a retarding 

 agency by the usual method based on the 

 positions of the tidal protuberances, was 

 found not only impracticable because of its 

 intricacies and theoretical uncertainties, 

 but because it involved an unrecognized 

 factor that renders the method misleading. 

 Moulton has found that all energy which is 

 converted into heat by the friction or im- 

 pact of the lunar tides and lost by dissipa- 

 tion, must in the present configuration of 

 the earth-moon system be taken from the 

 rotation of the earth and the revolution of 

 the earth-moon system in the proportion of 

 27:1, and that the rotation of the earth 

 must be reduced and the moon must retire, 

 and that this is independent of the kind or 

 phase of the tide. It is, therefore, only 

 necessary to estimate the total loss of en- 

 ergy by the tides and subtract the appro- 

 priate portion of this from the rotational 



energy of the earth to ascertain its retard- 

 ing effects. 



The data for such an estimate were put 

 into a tractable form, with large assump- 

 tions of tidal height and frictional zones, 

 and submitted to W. D. MacMillan for 

 computation by the formulas used by 

 engineers. The result gave an increase 

 in the day of one second in 460,000 

 years, or less than four minutes in 100,- 

 000,000 years. 



The geological evidences were discussed 

 on the basis of a series of spheroidal defor- 

 mations corresponding to a series of rates 

 of revolution computed by Slichter. It was 

 found that changes of rotation would cause 

 distinctive kinds of deformation of which 

 no distinct traces could be detected. The 

 distributions of the hydrosphere through 

 the geological ages were also found incom- 

 patible with the theory of appreciable 

 change of rotation. These negative evi- 

 dences of the geological record are in close 

 harmony with the computed effects on the 

 revised basis. 



Glacial Erosion in Wales: W. M. Davis, 



Cambridge, Mass. 



The mountains of north "Wales are pe- 

 culiarly significant in the problem of gla- 

 cial erosion, because they retain in part 

 forms little changed from those which are 

 not producible by normal erosion, but 

 which are eminently characteristic of the 

 forms that glaciers would produce if they 

 acted as eroding agents. In order to ap- 

 preciate the meaning of these contrasted 

 forms, it is essential that the observer 

 should have in mind a clear picture of the 

 forms appropriate to subdued mountains 

 that have been acted on only by normal 

 agencies. The general absence of such 

 mountains in western Europe has delayed 

 the recognition of the glacial origin of a 

 niunber of abnormal features. 



