A. W. Duff — Secondary Undulations, etc. 123 



Art. XIII. — Secondary Undulations Shown by Recording 

 Tide-gauges / by A. W. Duff. 



On recording tide-gauges at many ports rapid oscillations 

 are observed crossing and recrossing the main tidal record. 

 Mr. W. Bell Dawson* in a short article seems to have been the 

 first in recent years to recall attention to these " secondary undu- 

 lations," and well describes them as standing " in much the 

 same relation to the main tidal wave as a higher octave would 

 to a low musical note when their undulations are recorded 

 graphically." Others have given occasional attention to them, 

 especially Mr. F. Napier Denison,f whose two brief papers 

 suffer somewhat from a lack of detailed evidence for the " ten 

 chief points deduced " and too exclusive a concern with the 

 meteorological aspects of the question. No one seems to have 

 attempted to give a full account of the phenomena for even a 

 limited region. The best field for the study of the question is 

 apparently the Eastern coast of Canada bounded by the Bay 

 of Fundy, the Atlantic Ocean and the Gulf of St. Lawrence, 

 where, because of the great extent and complexity of the tides, 

 numerous recording tide-gauges have been established in the 

 interest of navigation. 



Four years ago I published;); some observations made at St. 

 John, N. B. The evidence advanced, depending on a calcula- 

 tion of the period of undulation from the dimensions of the 

 basins in the neighborhood, seemed to point strongly to the 

 undulations being of the nature of free vibrations of a par- 

 tially confined body of water under the force of gravity. Two 

 years ago I took advantage of a visit to Ottawa, Canada, to 

 examine (with the permission of the authorities of the Tidal 

 Survey of the Dominion of Canada, to whom my thanks are 

 due for their courtesy) the tidal records' from the Canadian 

 tidal stations and made extensive notes therefrom. Other 

 occupations interfered with the pursuit of the subject, but as 

 no one has since then taken it up, I have thought it well to 

 publish a brief outline of the information gathered together 

 with an examination of its bearing on certain proposed expla- 

 nations. 



Materials studied. 

 In order to make clear the extent of the data employed in 

 what follows, it may be stated that the tidal records from 

 twenty stations were examined in detail, these records covering 



* Trans. Roy. Soc. Can., i, 1895-96. 



\ Proc. Can. Inst., Jan. 16, 1897; April 23, 1898. 



% This Journal, iii, 406, 1897. 



Am. Jour. Sol — Fourth Series, Vol. X1T, No. 68. — August, 1901. 

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