SEISMIC EFFECTS 19 
It is evident at ‘once that these results are not concordant 
either in phase or amplitude, as each term gives a different 
value for what is presumably the ratio(1-%+). Before pro- 
ceeding farther we may remark that the general sensitiveness 
of the record was about I mm.=0”-04 and that much larger 
zero movements occurred than those expressed by the above 
terms. Thus it is open to doubt whether these discrepancies 
have any real significance, and whether the apparatus is really 
capable of giving more than the general order of magnitude of 
the effect. 
The ratio for (1 - 4+) given by Hecker’s results are for 
the lunar terms. 
0°68 for the E—W component. 
0°43 for the N—S component. 
Orloff (‘‘ Veroff d. Dorpater Sternwarte,” 1911) observing 
at Dorpat with Zollner pendulums in the geographical direc- 
tions obtained 
0°68 for the E—W component. 
0°59 for the N—S component. 
His apparatus was about four times as sensitive as Hecker’s 
and the individual results show better concordance than those 
of Hecker. 
It may be said that observers on the whole have obtained 
something like 2/3 for the value of (1-%+4) from pendulum 
observations of this particular lunar term, and this is also the 
value obtained by Darwin from his analysis of the fortnightly 
oceanic tides in the Indian Ocean. This apparent agreement 
seems at first to suggest a simplification of the theory 
of the values of Zand &, and that they might be calcu- 
lated on an equilibrium theory of the tides and so lead to a 
fairly accurate determination of the Earth’s rigidity, But 
Schweydar’s recent investigations show that this is not so, and 
that theoretically the matter is one of great complexity. 
We turn for a little to the theoretical side which we owe 
mainly to Lord Kelvin. The matter was one of life-long in- 
terest to him, and the investigations (Thomson and Tait, 
‘Natural Philosophy’) form the basis of most subsequent 
