Secondary Undulations of Oceanic Tides. 95 
These results confirm our view regarding the nature of the 
secondary undulation. 
The amplitude of the secondary undulation is usually in- 
creased by a low barometric pressure, which is approaching 
the bay. As a good example, we may cite the cyclone of 
Sept. 21-22, 1904, which was approaching from the Pacific 
side of Honshiu toward Hakodate. The undulations in the bay 
continued over a whole day, with a considerable amplitude — 
the maximum exceeding 40 cms. The periods of conspicuous 
undulation were 47 m, l-56 m, 9 and their octaves. 
The bay is especially sensitive to sea-waves ; and it is 
remarkable that waves originating on the American coasts 
have often been recorded by the tide-ga nge of the bay. The 
periods of the Ecuador wave, 1906, in the bay were 24 m, 2- 
26 m '0 and 48 m -3-51 m *8; while those of the Valparaiso one 
were 23 m '5-26 m and 47 m 0-52 m 0. The periods of the great 
sea-wave of Sanrikn, 1896, observed in the bay, were 23 m, 6 
and 47 m 3-52 m l; those of the small wave, 1897, in the same 
were 22 m l and 45 m, 5. 
(ii.) Aomori. 
The large bay of Aomori has the form of a dumb-bell, and 
is connected with the strait of Tsugaru by a wide neck. The 
observations were made at Aomori, when the centre of a deep, 
low pressure was approaching the district from the Japan- 
sea side. On this occasion a regular undulation of 103 m 
TSl/C^RU ST/f. \ d/H/HATO 
appeared on the record and continued for a day and a half. 
Upon this an undulation of a period ranging from 23 m, 4 to 
26 m, 3 was superposed. Besides, a period of 295 m could also 
be traced. 
The undulation of 103 m is probably the lateral oscillation 
of the bay, and that of 295 m the fundamental oscillation 
having its node at the mouth. The calculated periods 108 m 
and 284 m are thus in a fair agreement with these observed 
periods. The corresponding periods as given by our model 
