SECONDARY UNDULATIONS OF OCEANIC TIDES. 



83 



of observation, it is probable that the wave corresponds to the 

 oscillation proper to the bay with the shorter period, probably 

 superposed on the longer period. The wave took 24" 57'" to 

 arrive at Hakodate across the Pacific. 



As in the former case, we calculated the mean velocity of 

 the sea wave with the result given in the following table : — 



Thus the mean velocity of the sea wave fairly coincides 

 with that between Shimoda and San Francisco ; it is decidedly 

 less than the value of x/gh 



The terrible earthquake of Iquique on May 9, 1877, also 

 caused destructive sea waves, which were felt across the basin 

 of the whole Pacific, from New Zealand in the south to 

 Japan and Kamschatka in the north. In Japan, the waves 

 were observed at Hakodate, Kamaishi and the coast of 

 Kazusa. 



The earthquake originated at 8"2()'" p.m. on the 9th, and 

 the consequent sea waves broke on the shore of Iquique 30'" 

 afterwards with disastrous eflect. At 6" 21'" a.m. on the 10th, 

 a group of sea waves suddenly invaded the bay of San Fran- 

 cisco (PI. XLIX, Fig. 2) and put the bay water into oscillation ; 

 the oscillation seems to have been renewed at 2" 50'" p.m. by 

 another group of incident waves. The oscillations continued 

 over 2 whole days ; their periods of oscillation in comparatively 

 regular trains were 17.3'", 27.8'", 34.3"^ and 47.4'". Tlie most 

 conspicuous periods were 34.3'" and its octave 17.3'", tlie former 



