1445 
cos Y, — COS Ff, 
sin @. — sin 
After the substitution of and si ¥ 
* in which 
a a Pi = Po 
| ; : 
PP = 11278 we get the following equations 
+ 0.415 p + 0.874¢ = — 10.1 
+ 0.750 p + 0.6141¢ =— 9.6 
+ 0.940 p + 0.230¢ = — 5.8 
+ 0.948 p —0.195¢=-+ 1.7 
+ 0.772 p — 0.529 ¢ = + 11.0 
+ 0.447 p — 0.858¢ = — 4.2 
+ 0.036 p — 0.967 ¢ = — 13.4 
— 0.382 p — 0.889 ¢ =H 2.9 
— 0.727 p —0.689¢=-+ 1.6 
— 0.930 p — 0.265¢= + 1.2 
— 0.954 p + 0160g =H 9.0 
— 0.793 p + 0.554¢g=-+ 7.4 
— 0479p + 0.841g=+ 41 
— 0.072 p + 0.965¢ = + 3.3 
Solving these by the method of least squares, we get 
p—— 4.40, qg= + 0.42, 
therefore 
h = 4.42 sin (p + 174°33'). 
The mean error of the unit of weight (mean of two consecutive 
months) is + 51.5 mm., the mean errors of p and q are + 2.86 
and + 2.89, and the probable errors + 1.93 and = 1.95 millimetres. 
4. So far, we may deduce from this that the periodicity of the 
sea level in a period of 431.24 days is presumably real, although 
considering the small amount of this. variation and the comparatively 
large value of the mean errors, a more detailed investigation as to 
the probability of the results is desirable. 
For this purpose I have in the first place calculated the mean 
error of the unit of weight in another way, namely by taking 
the yearly means, and in the assumption of a small change in the 
sea level, proportional to the time, determining the mean error of a 
yearly mean and therefrom the mean error of the unit of weight; 
I. found for the latter value + 93.3 mm., much greater than the 
first value given. This shows that there are fairly large systematic 
v4 
Proceedings Royal Acad. Amsterdam. Vol. XY. 
