ii8 A. A. MICHELSON 



gave the following results, in which R is the ratio of the observed 

 amplitude to the calculated, and the phase acceleration: 



E.-W. . . . . .0.72 —0.4 hour. 



N.-S ..0.66 +1.0 " 



It appears therefore that the diurnal period gives for the ampli- 

 tude ratios numbers which are decidedly in better agreement than 

 those furnished by the semi-diurnal period. 



It is to be noted that while the agreement between the E.-W. 

 and the N.-S. results is considerably improved, the value of R for 

 the E.-W. direction has not been altered, whereas according to 

 Schweydar's investigation it should have been much larger (0.90 

 or more). It may be, however, that first, in consequence of the 

 smaller number of periods entering the calculation, and secondly, 

 on account of the smaller value of the resulting amplitude (41 : 100), 

 these numbers have a considerably larger probable error than that 

 of the semi-diurnal period. 



Possibly a closer analysis of the actual ocean tides would show 

 that the effect is small for the E.-W. direction, while in the N.-S. 

 direction it may be considerable. 



Regarding the acceleration of phase, it may be noted that the 

 difference between the E.-W. and the N.-S. direction is much 

 greater for the diurnal period than for the semi-diurnal, whereas, 

 if the results of the latter were seriously affected by the ocean tides, 

 the reverse should hold. The mean of the semi-diurnal accelera- 

 tions is 0^03, a quantity so small that it is within the probable error. 

 Taking this value together with o . 70 as the ratio of the observed to 

 the calculated amplitudes, the corresponding values of the earth's 

 rigidity n and viscosity e are: 



n= 8.6X10" c.g.s. 

 6 = 10.9X10^^ c.g.s. 



This calculation is based on the assumption of uniform rigidity 

 throughout the body of the earth, a condition which is certainly 

 not fulfilled; and that as the time increases in arithmetical progres- 

 sion the stresses diminish in geometrical progression. It is clear, 

 however, that the earth's rigidity is greater than that of steel. If the 



