76 K. HONDA, T. ^lERADA, Y. YOSHIDA, AND D. ISITANI. 



It will be seen from the above table that in most cases, 

 the period calculated by the simplest formula (1), that is, 



agrees fairly well with those actually observed. Thus for many 

 cases, the corrections due to the mouth and the variation of the 

 section seem to be superfluous. This probably arises from the 

 fact that in many bays, the correction due to the section nearly 

 cancels the mouth correction. For many bays have the form 

 gradually contracting and the depth decreasing, as we approach 

 towards the end, so that the correction due to the variation of 

 the section is negative. The mouth correction being always 

 positive, the two corrections usually tend to annul each other. 

 As exemplified in the cases of Ofunato and Tsuruga, the total 

 correction nearly vanishes for many bays, and then results an 

 apparent validity of the simplest formula. If the mouth of a 

 bay be contracted and the depth be shallower than in the in- 

 side, the correction due to the section is positive, so that the 

 calculated value by the simplest foi'mula decidedly falls short of 

 the observed value, and can only be brought into coincidence 

 by taking the tw^o corrections into consideration ; a good example 

 of this is furnished in the case of the Bay of Aomori. That 

 the calculated periods for the bays of Mororan and Okirai which 

 have rather narrow mouths, are a little less than the observed 

 values, is also explained on the same view. 



§ 8. SEA WAVES AND SECONDARY UNDULATIONS. 



As we have already remarked. Professor F. Omori found 

 that the periods of sea waves observed in a bay are the same 



