( 531 ) 

 whilst we found above 



For the difference in phase we found a constant part of 7 or 



— B t *^^ ^ = ^ 



2n ^ %isT) T K' 



For angles of + 23°, found for Cheribon for a shorter duration 

 of the vibration, we may write here approximately 



f{sT) ^T 

 tfj(sT) K' 

 So the ratio of amplitudes becomes 



4 jt' 

 1 + 



X 1 + c' f{s T) L* ' K"- 

 A_ Q \ 1 ^^ Q 



X I -i-c' T\/K"' -\- 4 ji' l + c'T" 



For 1 -(- c' we find according to La.mb-Schuster for that part of 

 the potential which is to be expanded in terms of a spherical function 

 of order 2 (for that part which is to be expanded in terms of spherical 

 functions of a higher order, the increase is quicker). 



constant 



So for higher frequency (for duration of half a vibration = 1 minute 



1 

 Ö is 7200) is about constant. 



A 1 



So we get — proportional to — . 



The observations, however, give for Cheribon and Anjer pro- 



I 8/1 



portionality with IX --^ (for still smaller T, even inversion, and for 



I ^ /\ 



Seraarang and Soerabaja proportionality to \X — . 



36 



Proceedings Royal Acad. Amsterdam. Vol. X. 



