ANNUAL MEAN SEA LEVEL ALONG THE JAPANESE COASTS 735 



which shows that the Unear correlation is insignificant for the year-to- 

 year variations of the uncorrected sea-level. 



(ii) Kushimoto— The datum line falls 17.55 cm. from 1900 to 1928, 

 while the mean sea-level rises 20.0 cm. in this period. 



(iii) Shimotsu-The datum line falls 27.5 cm. from 1928 to 1950, 

 and the mean sea-level rises 25.2 cm. in this period. 



(iv) Uwajima— The bench mark No. 4589, situated in Uwajima 

 City, rises 8.9 cm. in the period 1897-1935, and falls 4.3 cm. in the 

 period 1935-47. These results are in fair agreement T\ith the progres- 

 sive sea-level variation shown in Figure 2. 



(v) Tonoura— The datum line falls 5.0 cm. from 1944 to 1950, 

 while we have the gradual rise of the progressive sea-level trends (about 

 3 cm.) in this period. 



Thus, the vertical land deformation is likely to be closely related 

 with the progressive sea-level variations. However, the relations are 

 doubtful for the year-to-year variations. 



5. Tmr. of 18.6-Year Period 



The longitude of the moon's ascending node varies with the 18.6- 

 year period, and accordingly the obliquity of the moon's orbit varies 

 from 18.3 to 28.6. It is the origin of the 18.6-year period tide. There- 

 fore, it is included in Darwin's expansion of equilibrium tides. But 

 the theoretical amplitudes are, similarly as the other component tides, 

 generally smaller than the computed values. 



6. OCEANOGRAPHICAL EFFECTS 



The oceanographical effects are also thought to be important. 

 However, at least until noAv, the numbers of the oceanographical sur- 

 veys are too small to find out the mutual relations. The only available 

 data are found for the variations of Kushimoto. 



The repeated observations are made for the fixed section off 

 Shiono-Misaki, and the year-to-year density variations in the upper 

 layers can be computed for the period 1925-31. The sea-level varia- 

 tions caused by this origin /?,; are computed by Nomitsu's method (8), 

 and shown in Table HI. The variations of the Kuroshio currents are 

 also investigated for this region by Uda(9)(10), and the sea-level rise 

 measured from the current axis is easily computed by the formula 



, If sin ^ , _ 



^o = — LlL 



g 

 Avhere u is the annual mean speed of the Kuroshio at the surface of 



this area, and L is the corresponding current width. The results of 



computation are also shown in Table III. 



