122 Messrs. K. Honda, T. Terada, and D. Isitani on the 
depression prevalent in our sea. It is in all probability true 
that the barometric fluctuations constantly going on at a 
cyclonic centre, acting in an impulsive way, may give rise to 
a train o£ long waves whose wave-lengths are comparable 
with the dimensions of the centre. 
Abnormal upheavals of sea-level have also been frequently 
observed on our coast. In some cases the level gradually 
rose and fell with the passing cyclonic centre, while in others 
the sea was abruptly upheaved, apparently by the action of 
strong gales. On one occasion a considerable rise of the level 
was observed, when neither cyclone nor earthquake was 
reported. 
It may be added here that in some bays remarkable secondary 
undulations occurred in ordinary calm weather, although 
there was no cyclone in the neighbouring sea. These undu- 
lations seem to be associated with the unstable distribution 
of atmospheric pressure. For example, the abnormal undu- 
lations in Nagasaki known as " abiki " are usually accom- 
panied by devious isobars and twin-centres of low pressure. 
§ 8. Oscillation of large Bays and Anomaly of Tides. 
Thus far we have generally discussed secondary undulations, 
the periods of which are much shorter than those of the prin- 
cipal tidal components, viz. the diurnal and semi-diurnal. 
We will now 7 proceed to consider those undulations of much 
longer periods, that commonly exist in the tides of very large 
inlets or estuaries. 
Exaggeration of oceanic tides, which takes place in shallow 
seas and in estuaries, has often been explained merely by 
Green's law of amplitude*. Airyf attempted to explain 
anomalies of tides observed in some rivers, by the considera- 
tion that for a wave of finite amplitude different parts of the 
wave-profile travel with different velocities ; but his argument 
has been proved untenable J. Again, inferior tidal components, 
known as compound tides or over-tides, which become con- 
spicuous only in shallow basins, have been explained on the 
analogy of combination tones in acoustics §. It seems to us, 
however, that the theory alone is not sufficient to account for 
the facts that in some gulfs or bays the amplitudes of superior 
tides are often comparable with those of the proper tidal 
components, and also that most pronounced, compound tides 
* Green. Camb. Trans, vi. 1837 ; Math. Papers, p. 225. 
t Airv, ' Tide and Waves,' Art. 198. 
% McCowan, Phil. Mag. [o] xxxv., 1892. 
§ VV. Thomson, Proc. Roy. Soc. vii. G. H. Darwin, Brit. Assoc. 
Report, 188. 
