RIGIDITY OF THE EARTH 



117 



to 0.85 and o . 64 respectively. A similar correction applied to the 

 results of these experiments would give, instead of 0.71 and 0.52, 

 the values 0.99 and o. 73. The E.-W. value would mean that the 

 earth's rigidity is practically infinite, and it is undoubtedly too high. 

 The ocean is, however, anything but uniform in depth, and 

 this and the irregularities in coast lines, make an accurate calcu- 

 lation of the disturbing effect of the ocean tides almost impossible. 

 Accordingly Schweydar, considering that the results furnished by 



14 



16 



24 



26 



Fig. 16. — N.-S. Mean of observations of diurnal Lunar tide, 

 observed values ; full curve, o . 5 of calculated. 



Dotted curve, 



the consideration of the semi-diurnal tides is not reliable, investi- 

 gated the problem of the diurnal period, especially that corre- 

 sponding to the "dechnation tide" whose period is 25'^8i2. The 

 dynamical theory shows that for an ocean entirely covering the 

 earth, such tides should vanish; a result which is approximately 

 true, at least for the Atlantic. 



This analysis applied to Hecker's observations gives 0.85, as 

 the value of the ratio, which, it will be noticed, agrees with the 

 value for the semi-diurnal period when corrected for the calculated 

 perturbation of the ocean tides. 



The result of grouping the present observations into six groups 

 of two periods each (of 25^81) is reproduced in the graphs of Figs. 

 15 and 16. 



These were analyzed by means of the harmonic analyzer, and 



