Activities in the Tokyo University 



In 1942 Koji Hidaka, who has been working at Kobe for sixteen 

 years, was appointed the professor of the Tokyo Imperial University 

 and has given ever since the lectures on physical oceanography in the 

 faculties of science. 



In 1943 Hidaka gave a theoretical investigation on the motion of 

 water in an enclosed sea rotating with the earth, showing that an external 

 force can produce the same motion from the surface down to the bottom. 

 Similar attempt was tried in case of wind currents in a viscous water, 

 but T. Iti3^e showed the solution is not possible. 



In 1943 Hidaka showed that the stream lines in the two-dimensional 

 wind circulation in a lake can be compared to the buckling of elastic 

 plates built in along the portion corresponding to the bottom, while, 

 a movement is applied on the remaining straight portion corresponding 

 to the wind-driven surface of a lake. This theory was satisfactorily 

 proved by later experiments with steel plates. 



In 1944 Hidaka published his results of calculation on the develop- 

 ment of surface slope and currents in an enclosed sea induced by winds, 

 use being made of a pair of simultaneous integral equations of Volterra 

 type. 



In 1945 Hidaka tried to use the non-protected reversing thermometer 

 for shallower seas and lakes. For this purpose it was necessary to 

 construct a thermometer with pressure coefficient about ten times as 

 large as those hitherto used. S. Watanabe actually constructed this. 

 The observations were made in Tokyo Bay with some results. 



In nearly the same year R. Takahashi, of the Earthquake Research 

 Institute, Tokyo University, published a series of important theoretical 

 investigations on the destructive sea waves, or tsunami. He studied 

 the nature of oscillations responsible for the possible sources assumed 

 on the bottom of the sea. In 1948 he discussed the occurrence of tsunami 

 waves by a travelling disturbance on the floor of the ocean. 



In 1945 Hidaka devised a method of integrating the differential 

 equations of drift current, being based on Y. Takahashi's idea. This 

 method can be applied to the case of wind stress varying with time. 



He examined the method of location of motionless layer in the sea 

 and concluded in 1946 that the motionless layer corresponds to the depth 

 where the second vertical space gradient of salinity vanishes. After- 

 ward M. Miyazaki in 1946 derived a similar conclusion together with 

 the method of location of these layers. 



Hidaka is now studying a qualitative analysis of tides in which he 

 hopes to separate the influences of sun, moon, and meteorological effects 

 distinctly, analysis being made on the tide heights as the functions of 

 the hour angles and distances to the earth of the sun and moon. This 

 seems unsuitable to the prediction, because the mechanical operation 

 appears to be very difficult. 



In 1947 Hidaka and S. Hikozaka applied J. Proudman's theory of 

 diffraction of tidal waves to the distribution of 1946 tsunami height 

 alond the coast of Kauai Island, Hawaii, which is approximately circular 

 in form. 



Kozo Yoshida has been showing activities from 1944 on in the 

 practical study of ocean waves and surfs as well as the theoretical investi- 

 gations of long and surface waves, notably his investigation on the 



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