SECONDARY UNDULATIONS OF OCEANIC TIDES. 99 



afternoon of September 28, 1902, a remarkable cyclonic center 

 crossed over the northern part of Ilonshiii (PI. XCW) and the 

 tide-gauge at Ayukawa showed remarkable secondary luidulation 

 with the period of about 7'" (PL LXI, Fig. 3), which lasted for 

 more than 12 hours. The maximum amplitude recorded was 

 about 1 m., nearly at the time of arrival of the cyclonic center. 

 It is to Ije remarked that in these examples the periods of long 

 waves with remarkable amplitudes are nearly equal to those 

 peculiar to the bays. 



In the above examples, the beginning of the remarkable 

 undulation is well defined and its connection with the presence 

 of cyclonic center is very clear. On the other liand, there are 

 examples in which remarkable secondary undulations lasted for 

 a very long time during cyclones passing along our land, the 

 beginning being not (j[uite marked. Generally speaking, the 

 duration of large secondary undulations seems to depend on the 

 width as wt^I as the velocity of the cyclonic area. 



There are also cases, in wdiicli a remarkable undulation 

 appeared, when neither a cyclone nor an earthquake was 

 reported. As we have already remarked, the mareograms of 

 Nagasaki afford mauy good examples of this sort of undulation. 

 To take another example, the Kushimoto mareorgram (PL LXII, 

 Fig. 1) on February 8, 1904, is marked with a considerable 

 undulation with the periods of 13'", 20"'-2G"\ etc., which lasted 

 from the morning till the next day, the greatest amplitude being 

 nearly GO cm. The weather chart indicates no cyclone and no 

 wind in the neighbourhood of the district, but low pressures 

 reigned over the northern part of Hokkaido and also over the 

 Pacific in tlie south of Ilonshiu (PL XCY), while high pressure 

 prevailed over the continent. The remarkable undulation seems 



