50 EIGHTH PACIFIC SCIENCE CONGRESS 



present in a shallower level. He mentions this trouble is partly due 

 to the difficulty in locating this discontinuous layer by simply measur- 

 ing the submarine illumination (OM, 1, 1949, 43-47). He also stu- 

 died the optical significance of the transparency measured by Secchi's 

 disc. He concludes that the transparency of sea water should be defined 

 as the depth at which we cannot distinguish the difference in colors of 

 the disc with the surrounding water, in addition to the difference of il- 

 lumination (OM, 4, 1950, 129-136). He also pointed out that the ex- 

 tinction coefficient is a constant peculiar to sea water, independent of 

 the altitude of the sun and amount of clouds. He determined the re- 

 lation between extinction coefficient and wave length of light and ob- 

 tained a standard value of extinction coefficient for each of Forel's 

 scales of color of the sea. He divided the extinction coefficient of sea 

 water into the absorption and scattering coefficients. According to his 

 observations with a photometer of photoronic cell type, scattering coef- 

 ficient occupies only 10% of the extinction coefficient. This fact re- 

 quested him to assume the existence of a colored substance in sea water. 

 He determined the relation of transparency and extinction coefficient 

 and showed that the formula at Atkins and Poole only holds for small 

 value of transparency. This conclusion agrees with observations very 

 closely (KJ, 4, 1952, 268-324). K. Hishida also made a photometer 

 of the photoronic type and found that the submarine illumination has 

 much to do with the hydrography (MMOR, 2, 1951, 21). 



A theory of transparency of sea water was propounded also by T. 

 Nan'niti, who derived a theoretical relation between transparency and 

 hydrographic factors (MGP, 3, 1953, 195-201). 



Annual variation and correlation between color of the sea, trans- 

 parency and the plankton volume were studied by M. Koizumi. He 

 found that there are two maxima in the color and transparency of the 

 sea, that is, in summer and winter and two minima in spring and fall, 

 and that this variation reflects the seasonal change of plankton volume 

 which reaches a maximum in spring and a secondary maximum in the 

 fall. From this result a simple formula was obtained between them 

 (JOSJ, 8, 1952, 79-83). 



Sea Ice 



The intense studies on the sea ice in the areas around Hokkaido, 

 the northernmost island of Japan, have been made by K. Fukutomi 

 and his colleagues, K. Kusunoki, T. Tabata, T. Kashima, M. Saito, U. 

 Kudo, and others. They are published in the Japanese language in 18 

 papers entitled "Studies on Sea Ice" during the period 1949-52 (TK, 

 3-9, 1950-52). Kusunoki compiled a bibliography of Sea Ice in Japan 

 and made a list of references dated from 1892 to 1950 (JSSI, 13, 1952). 



