4444 
of 15 days. From all these mean sea levels, 49 in number, ¢orre- 
sponding to the same phase of the latitude variation, an average is 
then formed. In a similar way the averages are taken from the 
series of sea levels which correspond to the phases of the latitude 
variation 1, 2, 3,...13 months later than 31 January 1855. These 
14 months contain over 426 days, almost the entire CHANDLER period 
therefore. 
1 found for the deviations of these 14 values from their general 
mean : 
= 10.1 mim: 
— 9.6 
ee, 
+ 1.7 
+ 11.0 
= 4.2 
—13.4 
2.0 
1.6 
1.2 
9.0 
7.4 
4.1 
9.9 
+++++++ 
These numbers with the exception of the 4 and 5™ seem to show, 
a periodic variation, and the assumption is permissible that the 
sea level at Helder undergoes a periodic change in the course of 
431.24 days, and that the height, / days after the end of January 1855 
is represented by 
t 
h—a sin las 5A x 3609 + a, je sin (p +e,) —acos a, sin p + asin a, cos p 
=p sing + q cos p. 
The heights given in the above column are got by taking the 
average of the bi-monthly means; if at the beginning of the period 
p=p, and at the end y= p,‚, then that average is 
COS YY, — COS &, sin Y, — sin fp 
Hú - - cos a, + a sn Ct, 
fy fs Vitae 
or 
cos Ff, — cosy, sin f, — sin P, 
H = p —————_—_ 4+ q— ; 
Ai Tas PTP 
