SECONDARY UNDULATIONS OF OCEANIC TIDES. 79 



On the 24th, similar waves visited the Pacific coast from 

 Tosa to Izu. 



On the 23rd-24th, a regular train of sea waves was recorded 

 on the tide-gauges at San Francisco and San Diego (PI. XLTX, 

 Fig. 1). The average period of oscillation at San Francisco was 

 34.9'", whilst that at San Diego was 34.7"\ The wave took 12" 

 12™ and 12" 37'" to arrive at San Francisco and San Diego 

 respectively. 



Now, the Bay of San Francisco, as we have shown by the 

 model, can be put in the oscillation between Sausalito and 

 West Berkeley sides by waves incident on Golden Gate. The 

 period 34.9" falls a little short of the period of the binodal 

 oscillation of the bay. 



The Bay of San Diego is too long to be put in its uninodal 

 longitudinal oscillation ; the contraction of the bay near San 

 Diego also prevents the fandamental oscillation. The oscillation 

 between Quarantine wharf and San Diego, which also forms a 

 part of a trinodal oscillation of the whole basin, gives the period 

 of 34. ,5'". In this calculation, the depth was estimated from the 

 available charts to be 3.5 m., while its length was taken as 

 0.07 km. 



If the path, by which sea waves travelled from Japan to 

 America across the Pacific, be known, the velocity of propaga- 

 tion can be estimated. Now the sea wave, which has usually 

 a large wave length compared with the depth of the ocean, must 

 be refracted according to the condition of the bottom, so that it 

 is very difficult to know tlic path by which the sea wave 

 actually travelled through the ocean. We therefore conceived 

 several paths between the origin of the wave to the observed 

 station in question, of wliich we measured lengths, and also 



