Secondary Undulations of Oceanic Tides. 99 
probably the seiches between Awa and Otani. Calculated 
periods, corresponding to those supposed modes of oscillation, 
show a fair agreement with the actual periods. The experi- 
ments with the model also lead to the same conclusion. 
(vi.) Hososldma. 
Hososhima is an elongated bay on the eastern coast of 
Hiuga in Kiushiu ; here Kelvin's tide-gauge is constantly 
working. It recorded several sea-waves, which were origi- 
nated on the American coasts and which had travelled across 
the Pacific. Simultaneous observations were recorded at 
Hososhima and Isegahama, situated inside and outside the 
bay respectively. In the bay, extremely regular undulations 
Fig. 6. 
appeared superposed on the tidal wave, whose periods varied 
from 17 m, 8 to 20 m, 3 according to the tidal phase. In calm 
weather the amplitude of undulation amounted even to 25 cm. 
The period of the undulation slightly decreased as the tide 
passed from low water to high. The fundamental period, 
calculated to be 19 m *0, agrees well with the observed one. 
The change of the period caused by a change of depth due to 
tidal influence, has also the range which is to be expected 
from the theory. Besides, longer periods such as 34: m, 0- 
38 m, 7 and I3 m, 4-49 m, l are sometimes observed. 
Outside the bay, the undulation of the period 17 m, 8-20 m, 3 
is very faint, while the undulations of the longer periods are 
barely observable. By placing the diagram of a record taken 
in the bay upon the corresponding one taken on the open 
coast, we can distinctly trace undulations in the two records, 
which correspond to each other. If we bring the records 
of any two consecutive days into coincidence as regards 
the tidal phase, we observe the same succession of undu- 
lations. 
H2 
