134 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



The Origin of Ocean Tidal Secondary Undulations. By F. Napier 

 Denison, Toronto Observatory. 



(Read April 23, 1898.) 



Last year the writer had the honor of reading before the members of this 

 Institute a short paper, entitled " A Probable Solution of the Secondary Undula- 

 tions Found Upon Ocean Tidal Records." As the information then obtainable 

 was extremely limited, the important points were set forth as suggestions for criti- 

 cism. Since the publication and widespread distribution of your valuable " Pro- 

 ceedings " containing this paper, the writer has received numerous encouraging 

 letters bearing upon this subject from various quarters of the globe. 



In order to still further pursue this most engrossing and what is to be hoped 

 valuable investigation, arrangements were made by Mr. Stupart, Director of our 

 Service with the Marine Department at Ottawa, whereby the writer was granted 

 free access to all the Canadian Tidal records now under Mr. M. W. Bell Dawson, 

 Engineer in charge of the Tidal Survey, who also assisted me in every way possible. 

 Tracings were made from over 1,000 daily tidal records, showing different types 

 of undulations, from the following stations: — Halifax, Anticosti, St. Paul Island, 

 Forteau Bay, St. John, N.B., Father Point, and Point Levis; also the original 

 records were obtained from the temporary tidal stations at Carleton, P.Q., Pictou, 

 N.S., Souris, P.E.I., St. Peter's Bay, P.E.I.^ and the Grindstone Island Baro- 

 graph records from 1893- 1894 to study with the corresponding Anticosti tidal 

 traces, also tracings from several St. John, N.B., barograms. Upon returning 

 to Toronto these records were carefully studied in conjunction with the corres- 

 ponding synoptic weather charts at the Observatory. The result of this investiga- 

 tion clearly demonstrated that these undulations are due to the direct action of 

 atmospheric waves or billows, as they pass over the harbours or bays, which tend 

 to form minute undulations upon the surface of the water, and as these small water 

 imdulations advance farther into semi-enclosed basins become magnified as they 

 reach narrower and shallower portions where the tide gauges are situated. Permit 

 me briefly to summarize what has already been observed by others bearing upon 

 this interesting subject. 



In 1838 this phenomenon was observed at Swansea, England, where a regular 

 time interval of from fifteen to twenty minutes was noted. Some of these records 

 were sent to Sir George Airy, who was then unable to account for them. Admiral 

 Smythe referred to this phenomenon at Malta, where it had long been termed 

 ■' MirobiaS," and supposed to be due to distant storms. In 1878 Sir George Airy 

 read a paper before the Royal Society upon the tides of Malta, in which he speaks 

 of these undulations as simple harmonic curves^ whose heads are sometimes notched 

 as by the intermixture of small waves. That they had a marked time interval of 

 twenty-one minutes and a range of twelve inches amplitude, much exceeding that 

 of the lunar tides. He believed they were " seiches " similar to those discovered 

 by Forel upon the Swiss lakes, and supposed them due to a reflexive action from 

 the shores of Sicily and the African coast. Major Baird, of the Indian Tidal 

 Survey, referred to this phenomenon in 1868 as being most pronounced at the ends 

 of bays, but oflfered no explanation. In 1896 Professor Duff, of Purdue University, 

 studied these undulations at St. John, N.B., and Indiantown, and later presented 

 a paper before the Royal Society of Canada, in which he also classes them as 

 " seiches," due to some form of oscillation between the two sides of the Bay of 

 Fundy. He does not attempt any explanation for the abnormal movements often 

 observed during fine settled weather. Mr. H. C. Russell, of New South Wales, 



