SEISMIC EFFECTS 8I 
treated the two separately. His main point is, however, that 
while the corporeal tides may be computed at their equilibrium 
values, the oceanic tides must be considered dynamically. The 
differences of Hecker’s results in the N—S and E—W direc- 
tions are attributed to the unequal action of the oceanic tides in 
different directions, while 2 and & are substantially changed 
from what they would be on the simple theory, by terms de- 
pending on the oceanic tides. On certain assumptions with 
regard to the depth of the ocean he finds that the general 
rigidity of the earth may be from two to three times that of 
steel, and that the results obtained from the semi-diurnal lunar 
terms may thus be brought into accordance with the astrono- 
mical data. 
He concludes that the semi-diurnal lunar terms indicated 
by seismographs are not of much real value in determining the 
value of the earth’s rigidity. 
We may remark in passing that somewhat similar numerical 
results would follow by taking account of the Earth’s compres- 
sibility for one of the most important points obtained by Love 
(“ Problems of Geophysics’) is that the compressibility would 
substantially increase the estimated value of % without much 
affecting &, so that the experimental values when corrected for 
compressibility would lead to improved concordance and to 
higher values of the rigidity. 
Schweydar’s next step is to argue that the nearly diurnal 
lunar declination tide due to the potential 
AB 
ae 
is better adapted to give the value of / — #, because ona certain 
assumption as regards the depth of the ocean (which is not the 
same as that made in the discussion of the semi-diurnal term) 
the effect of the oceanic tides may be neglected. 
He gives the following results obtained at Freiberg i.S. 
with pendulums in azimuth 35° E of N and 55° Eof S. 
O.=imeg (1-& é) sin w cos*k w sin 2 ¢ cos (¢+A-4,) 
Pendulum I. 
Observed. 000412 cos (¢ — 273°). Computed. 0’’-00493 (cos ¢ — 280°). 
Pendulum II. 
Observed. 0’00318 cos (¢ — 248°). Computed. 0’00363 (cos ¢ — 249). 
6 
