Secondary Undulations of Oceanic Tides. 89 
coasts of Europe. In 1895 W. Bel] Dawson* read a paper 
before the Royal Society of Canada, in which he demonstrated 
the existence of secondary undulations of considerable 
amplitude. 
Professor Duff f concluded, from observations at many 
stations along the coast of the Bay of Fundy and the Gulf of 
St. Lawrence, that the periods of the secondary undulation 
were peculiar to each station, and that the phenomenon here 
partook of the nature of seiches excited by the low barometric 
conditions. H. C. Russell $ states that at Sydney the undu- 
lations are in most' cases due to atmospheric disturbances. 
Napier Denison§, of Toronto Observatory, made a systematic 
study of the subject in connexion with the barometric changes, 
and attributed the phenomenon to long waves generated by 
air waves of considerable wave-length, which accompanied 
the low barometric pressure. For several years Professor 
Giovanni Platania|| has been investigating the secondary 
undulations in the Gulf of Catania, as well as on other coasts 
of Italy, and has noticed that the oscillations of conspicuous 
amplitude occur in connexion with barometric disturbances. 
In the bays of Japan on the Pacific coast, the phenomenon 
is sometimes so remarkable that it is commonly known as 
Yota. In the harbour of Nagasaki it is called AbiJci ; and 
here the amplitude of undulation frequently exceeds 60 cms. 
This yota or abild is frequently observed during the calm 
weather which immediately precedes an approaching low 
barometric pressure. 
Professor F. Omori^f studied the secondary undulations of 
Ayukawa, Misaki, and Hososhima mareograms in connexion 
with his discussion of the several destructive sea- waves, and 
found that the periods of the waves are the same as those 
observed in ordinary cases. The records** taken from the 
tide-gauges at Indian coasts, of the waves which accompanied 
* Dawson : '-'Notes on Secondary Undulations," Proc. Roy. Soc. 
Canada, May 1895. 
t Duff: "Seiches on the Bay of Fundv," Amer. Journ. Sci. iii. 1897. 
« Periodic Tides," ' Nature/ lix. 1899. 
t Russell : " The Source of Periodic Waves," ' Nature,' lvii. 1898. 
§ Denison : " Secondary Undulations of Tide-gauges." Proc. Can. Inst. 
i. 1898. " The Origin of Tidal Secondary Undulations'," ibid. i. 1898. 
|| Platania : " Le librazioni del mare con particolare riguardo al Golfo 
di Catania," Atti del V. Congr. Geogr. Ital., Napoli, 1904. "I fenomeni 
in Mare durante il ferremoto di Galabria del 1905," 1907. "Nuove 
ricerche salle librazioni del mare/' 1907. 
51 Oinori : Publications of Earthquake Investigation Committee, xxxiv. 
1900. 
** Omori: Publications of Earth. Inves. Cornni. lvi. 1906; Proc. Tokio 
Math.-Phvs. Soc. ii. 1905. 
