124: A. W. Duff — Secondary Undulations 



a period of seven years, although the records from many sta- 

 tions covered a much shorter period. In all, the records of 404 

 tides or parts of tides that presented evidence of secondary 

 undulations were copied carefully on tracing paper. In addi- 

 tion, the tiles of the Atlantic Pilot Chart (monthly) and the 

 Canada Weather Map (weekly), were examined and in many 

 cases copied for periods corresponding to the tracings of tidal 

 records. From the Admiralty Charts of the region the width 

 and mean depth of many bays and channels were obtained. 

 To facilitate the work of any future investigator, I shall, so 

 far as possible, give the dates of occurrences noted (usually in 

 foot notes), but I find that occasionally my notes of dates are 

 somewhat imperfect. 



The period, extent and general nature of the undulations. 



.In the following statements of observed periods of regular 

 undulations, I have not, so far as I know, omitted any occa- 

 sions on which regular undulations could be observed no matter 

 what the period might seem to be (except in the cases of St. 

 John and Halifax, for which the records are too extensive to 

 be quoted in full). In reference to the fewness of these occa- 

 sions at certain stations, it is to be remembered that at many 

 places tide-gauges were maintained for a few months only. 



1. St. John, N. B. (on the Bay of Fundy). Here the undu- 

 lations are frequent, sometimes continue for as much as a week, 

 and vary in extent from an inch to a foot ; but, when very 

 slight, they are hardly distinguishable owing to the great 

 extent of the tide (at spring tides 28 feet). The undulations 

 are more nearly regular and periodic than at any other station, 

 the mean period (the evidence for which will be stated in 

 another connection) being 41 minutes. Occasional variations of 

 several minutes from the mean period are found, but slight 

 irregularities at times make the estimation of the period difficult. 

 The undulations occur about four times as frequently in winter 

 as in summer. 



2. Yarmouth^ N. S. (on the Bay of Fundy). The undula- 

 tions are very common especially near low tide when they are 

 usually present, and in certain extreme cases (e. g. Jan. 1, 1899) 

 nearly five feet in amplitude ; at high tide they are much less 

 marked. Frequently they are more or less irregular, whereas 

 at other times (e. g. Dec. 31, 1898) as many as ten regular oscil- 

 lations may be measured. From twelve records of low tide 

 which showed regular undulations the following mean periods 

 were deduced :* 28, 27, 34, 34, 28, 32, 26, 22, 31, 34, 28. 34, 



* J,une 26 (5 undulations); July 2 (6), 5 (5), 6 (4); Aug. 30 (7): Sept. 8 (5), 11 

 (6), 18 (5); Oct. 12 (6), 16 (4), 30 (8), 30 (4); Dec. 31 (10)— all in 1898. 



