SECONDARY UNDULA.ÏIONS OF OCEANIC TIDES. 25 



Dr. Imamura also obtained the undulation of the same periods 

 in 1902. 



The bay of Ryôishi is of a Y-shape, and consequently all 

 waves proceeding toward the bay are found at Eyôishi situated 

 at the end of the bay. On the other hand, the bay of Kamaishi 

 is somewhat crooked so that at Kamaishi near its end, the sea 

 is extremely calm giving rise to few short waves such as are 

 always observable in free coasts. A wave, whose wave length 

 is very large compared witli an obstacle, goes round the ob- 

 stacle ; but a wave whose wave length is very small, is screened 

 by it and the sea behind it is quite free from its influence. 



At Kamaishi and Ryôishi, we met with a storm on July 

 27-28 ; the character of the secondary undulations was not 

 altered, except tliat they were much superposed by zigzags of 

 shorter periods, and that their amplitude was somewhat in- 

 creased. 



(4) Kojirohama (July 26-31, 1904). Top. 20. PL YIII, 

 Fig. 3. 



Kojirohama is a small bay, south of the bay of Kamaishi ; 

 stations w^ere Kojirohama and Oishi, which are facing to each 

 other. The simultaneous observation showed that tlie phase of 

 the most prominent undulation is the same for these two stations. 

 The observed periods are lS.S'"-20.4'" and 24.6'", while the 

 calculated period is 26.0"\ 



It is remarkable to observe that the prominent period in 

 the bay is nearly the same as that of Kamaishi or Ryôishi. 

 Dr. Imamura also observed undulation of the same period in 

 the bay. 



(5) Yoshihama (July 28-Aug. 6, 1904). Top. 21. PL IX, 

 Fig. 1-3. 



