( 1231 ) 
n—l 
Rr(1 — ) 
n 
a 
7 a v Ac Os b HE a? 
e . 5 a pn ‚dp ) 2 
Bearing in mind that p + =—7 a ec find for small value of x: 
U 
d RT d 
ile = = + x ede 
aT Obi | da Jor 
according to (9) 
ne RT 1 
i —— a oe ) 
n| —— — | 
a 
or dividing by p: 
= s ——_ — 3 —____~_~ 
v—b Ev; 
nisi 
a 
: Ay 
is found to be somewhat greater than — , but 
8 
So the value of 
DO 
so little that our foregoing calculations can remain unchanged. 
Geophysics. — -“On tidal forces as determined by means of 
Wincuert’s astatic seismograph’’. By Dr. C. BRAAK. (Com- 
municated by Dr. VAN DER STOK.) 
(Communicated in the meeting of March 25, 1911). 
In a previous communication the E—W component of the semi- 
dinrnal lunar tidal motion of the ground at Batavia, as deduced 
from registrations of Wipcurrt’s astatic seismograph during the 
period of July to December 1909, was stated to be: 
0’’.0114 cos (2t—251° 53°), 
whereas the theoretical value is: 
0’’.0155 cos (2t— 270°) 
The registrations obtained during the following half-year have 
now been worked out upon the same plan and, in addition to this 
tide, the other principal tides have been calculated for the whole 
period of one year, except the semi-diurnal solar tide, which is 
strongly disturbed by the diurnal heat wave. 
These tides, enumerated according to their importance, are : 
1) These Proceedings XIII. 1910, p. 17—21. 
